my REsearch PROject final

Faisal Waheed MEng Chemical Engineering
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EVALUATION AND DEVELOPMENT OF PNEUMATIC
SPRING PARTICLE SIZE ANALYSER
Thesis submitted to the University College London for the degree of
Master of Engineering
By
Faisal Waheed
April 2011
Supervised by Professor Haroun Mahgerefteh
Department of Chemical Engineering
University College London
Torrington Place
London WC1E 7JE

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Abstract
This thesis describes the further evaluation and development of the Pneumatic
Spring Size Analyzer (MARK III) by conducting series of experiments. MARK III is the
latest instrument in the development of helical spring based technology. It is used to
determine the particle size distribution (PSD) of dry powders in the size range of 30
to 2000 μm.
The unit functions by discharging the particles of the powdered sample through
aperture (gap between two coils) of a stretched helical spring using pressurised air.
The PSD is obtained by plotting cumulative mass percentage of the discharged
particles against corresponding particle size.
The core of this thesis consists of four sections of experimental study conducted on
MARK III to evaluate and analyse the performance and to suggest improvements for
possible flaws.
In the first section of the study, PSD data for MARK III was compared with sieves PSD
data. The second section of the study is to find an operating pulse rate, which gives
the best performance. This is done so by varying size ranges combined with constant
pulse rate and varying pulse rates combined with same size range. The experiments
were carried out using glass ballotini mass sample in the particle size range of 180-
1000 μm. Results obtained in third section of the experimental study were very
interesting. This section consists of the experiments based on principle of fluidisation.
In this set of experiments, the pressure drop, for different masses for particles size
ranges of 212-850, was measured using manometer. The pressure drop data was
plotted against the air flow rate. Effect of changes in particle masses and different
size ranges was discussed. Also, an in-situ mass measurement using fluidisation was
considered. In the last section of experimental study, newly installed digital calibre
was compared with old method of measuring spring length. This was done with the
help of error analysis.

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Acknowledgements
First of all, I am grateful to Almighty Allah, the most beneficent, the most merciful,
who bestowed on me the wisdom and perseverance to pursue this research project.
All praise is to Allah and all the benefits from this project are by his grace.
I would like to express my deepest gratitude to Professor Haroun Mahgerefteh, for
his patience and supervision throughout the year and for providing me with this
great opportunity of undertaking this project.
I would also like to thank Aisha for helping me throughout on everything. She is
always available for help. She is not only very helpful, but also a great human being. I
wish her all the best for her PhD.
I also want to thank for the support and assistance of the technical staff especially
Eric and Graham for being patient with me.
Most importantly, I would like to thank my family for their support, patience and
encouragement throughout this research project.
Last but not least, I would like to express my gratitude to my friends and colleagues
for their support.

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Table of Contents
CHAPTER 1| INTRODUCTION ..................................................................................7
CHAPTER 2| LITERATURE REVIEW .....................................................................11
2.1. CHARACTERISTICS OF THE PARTICLES .................................................11
2.1.1. PARTICLE SHAPE...................................................................................11
2.1.2. PARTICLE SIZE .......................................................................................13
2.1.3. PARTICLE SIZE DISTRIBUTION ..........................................................14
2.1.4. PARTICLE DENSITY ..............................................................................16
2.2. SAMPLING ......................................................................................................18
2.2.1. CONING AND QUARTERING ...............................................................18
2.2.2. SCOOP SAMPLING .................................................................................19
2.2.3. TABLE SAMPLING .................................................................................19
2.2.4. CHUTE SAMPLING.................................................................................19
2.2.5. SPIN RIFFLING METHOD......................................................................19
2.3. PARTICLE SIZE MEASUREMENT TECHNIQUES ....................................21
2.3.4. SIEVING....................................................................................................22
2.3.2. SEDIMENTATION...................................................................................23
2.3.3. MICROSCOPY..........................................................................................24
2.3.4. LASER DIFFRACTION METHOD .........................................................25
2.4. SPRING SIZE MEASUREMENT TECHNIQUE AND DEVELOPMENT ...26
2.4.1. BASIC PRINCIPLES OF OPERATION...................................................26
2.4.2. VIBRO-SPRING PARTICLE SIZER METHOD (MARK I) ...................27
2.4.3. MODIFIED VIBRO-SPRING PARTICLE SIZER (MARK II) ...............29
2.4.4. HAND-HELD PARTICLE SIZE ANALYSER METHOD ......................33
CHAPTER 3| APPARATUS AND DETAILS OF MARK III ....................................35
3.1. PNEUMATIC SPRING PARTICLE SIZER (MARK III) ...............................35
CHAPTER 4| RESULTS AND EVALUATION OF MARK III ................................40

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4.1. COMPARISON WITH SIEVE DATA ............................................................41
4.2. AIR PULSE RATE AND PARTICLE SIZE RANGES ...................................43
4.2.1. DIFFERENT PARTICLE SIZE RANGES AT CONSTANT P.R............43
4.2.2. CHANGING PULSE FOR SAME PARTICLE SIZE RANGE................48
4.3. FLUIDISATION...............................................................................................51
4.3.1. FLUIDISATION AT DIFFERENT MASSES AND PARTICLE SIZES .52
4.4. COMPARISON BETWEEN DIGITAL AND ANALOGUE CALIBRE ........60
4.4.1. ERROR ANALYSIS .................................................................................61
CHAPTER 5| CONCLUSIONS AND FUTURE WORK ...........................................64
5.1. CONCLUSIONS...............................................................................................64
5.2. FUTURE WORK AND IMPROVEMENTS....................................................67
5.2.1. NEW IDEAS AND CONSIDERATIONS ................................................68
REFERENCES ............................................................................................................71
APPENDICES .............................................................................................................74
APPENDIX A1........................................................................................................74
APPENDIX A2........................................................................................................75
APPENDIX A3........................................................................................................78

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CHAPTER 1| INTRODUCTION
Human knowledge of the powders and particulates has been surprisingly not any
way near as much as their use. The lack of knowledge of powders can be shown by
the fact that for many years it was thought that powders only exist as solids.
Recently it was discovered that, this classification has been upset because when
powders are aerated, they behave as liquids and when suspended in a gas, they take
some of properties of the gas (Allen, 1997).
At present age, many products which are manufactured in industry are in powdered
form. In fact, almost every industry uses powders at some point in the process.
These products include detergents, pigments, cements, fertilizers, agrochemicals,
tooth powders etc. (Allen, 1990,1997; Arai, 1996).
Powders are dry solid materials composed of innumerable microscopic particles.
These microscopic particles applied vastly in many industries mainly because of their
size. It is this size of these particles which has telling effect on the properties of the
powder. For example, soil experts and civil engineers examine the particle size and
size distribution of the soil in relation to agriculture and bearing ability respectively.
Chemical engineers study pore sizes and surface properties of the catalysts to
produce fuels. It is also used to determine the setting time of cement; the potency of
the drugs and taste of food in food industry. Hence the particle size and size
distribution is of great importance (Arai, 1996; Allen, 1997; Rhodes, 2008).
The importance of powders can be perceived by the fact that the impact of
particulate products on US economy was estimated to be one trillion US dollars.
Almost 30% of all the products worldwide are in powdered form. Approximately all
the aspects of the technology in relation with the handling, manufacture and
applications of the powder, require the knowledge of the particle sizing (Allen, 1975;
Allen, 1997; Rhodes, 2008).

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This increasing importance of powders and particulates in different industries has
resulted in invention and development of many techniques for particle size analysis
and distribution. These techniques are based on different principles of operation and
vary in all forms. Some of the available techniques are sieving, sedimentation, laser
diffraction, electrical sensing, permeability and microscopy. Most of these
techniques are expensive, fragile; require complicated operating procedures,
incapable of handling big masses of sample (Arai, 1996; Allen, 1997; Patel, 2001).
In 1991, Mahgerefteh and Al-Khoory developed a novel technique for particle size
determination. The technique is based on the principle of vibro-fluidization. The
technique involved a container which is partly filled with a powder; when vibrated in
lateral direction, the particles inside the container become fluidised. The method
was limited to an average particle size measurement and could not produce particle
size distribution for the sample of powder (Al-Khoory, 1991).
In 1996, a new novel technique was developed by Mahgerefteh and Shaeri based on
the same principle of vibro-fluidization but this time, instead of a container; the
technique involved a horizontally held closed coil helical spring filled with powdered
particles. The spring is stretched along its length and vibrated vertically. As the result
of the vibration, the particles become fluidized and smaller particles discharge
through the spring coil gaps. The discharge particles can then be weighed using
conventional balance. The size of the discharged particles is directly related to the
extension of the spring. This technique had potential to overcome the problems
associated with previously known conventional techniques (Shaeri, 1996).
In 2001, Patel made an improvement to this technique based on same principle of
the discharge of particles from a horizontally suspended vibrating spring. The
difference in this technique is that the spring is mounted at one end of the double
beam cantilever system pivoted along its length and development of in-situ
continuous mass measurement powder samples within the system (Patel, 2001).

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The evolution of the technique so far was remarkable and had evolved many
advantages such as robustness, simplicity and in-situ mass measurement. However,
it still could not handle more than 10g of a sample which is very unlikely to be
representative (Kerdvibulvech, 2008).
In 2004, Kamugasha took this technique to next level by developing Pneumatic
Spring Particle Size Analyzer (MARK III). The unit has same basic principle as the
previous devices. However, the spring is vertically held and the particles inside the
spring are agitated by the pressurised air from the bottom rather than the vibrations
(Kamugasha, 2004).
The MARK III was further developed in 2008 by Kerdvibulvech by introducing an
almost built in weighing mechanism (kerdvibulvech, 2008).
Also, in 2008 a handheld spring size analyser was designed to help develop and study
the technique even more. The agitation in the handheld device was achieved
manually by shaking the device (kerdvibulvech, 2008).
This thesis comprises six chapters.
Chapter 2 addresses the fundamentals and characterisation of the particles. In this
chapter, the size, shape and density of the particles are defined and explained.
Different types of PSD and methods of representing these methods are discussed.
Some of the conventional techniques for particle size measurement and their
limitations are also discussed. Lastly, a brief history of development and design of
helical spring method is addressed.
In chapter 3, the apparatus and experimental methodology of the related
experiments are discussed. This includes the methodology of comparison of PSD
data from MARK III and a stack of sieves, application of fluidisation and effect of
changing pulse rate. Additionally, a comparison was made between newly installed

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digital calibre to measure of extended length of spring and old way of measuring the
spring length.
The chapter 4 consists of results and discussion of the experiments carried out. The
results, to evaluate the performance of the MARK III, involved PSD data for sieves
and for spring in MARK III. Chapter 4 also included the PSD data for different pulse
rates and particle size ranges and their discussion. Moreover, it involved the results
and discussion of the experiments based on principle of fluidisation.
Chapter 6 is the ultimate chapter of the thesis which comprised of the general
conclusion, main findings of the thesis and the recommendations for the future work.

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CHAPTER 2| LITERATURE REVIEW
Particulate materials and powders are used more or less in every process industry.
Particulates are being used in food processing, pharmaceuticals, chemical, mineral
processing, plastics, detergents, paints etc. The study of any powder, granular
material or any other particulate is based on the characteristics of the particle which
makes that material up. A particle is characterized by its shape, size and density. The
determination of particle size, shape and size distribution is fundamental in
determining the properties of bulk powder. The population of particles is shown by a
Particle Size Distribution (PSD). The method used to determine a PSD is called
Particle Size Analysis (particle sizing) and the equipment that is used for particle
sizing is called Particle Size Analyser (T.Allen, 1997;Clift et al., 1997).
In literature review, brief information on particles characteristics, distribution and
different techniques used for particles sizing is described. The techniques reviewed
include those based on sieving, sedimentation, optical and other techniques.
2.1. CHARACTERISTICS OF THE PARTICLES
It is of major importance to determine the physical characteristics of the particles as
these can influence significantly the fluid-particle interaction and therefore the
behaviour of fixed and fluidized beds.
2.1.1. PARTICLE SHAPE
Particle shape is an important characteristic of the particle. The shape of a particle
affects the packing of the powder, which as a result has an impact on other
properties; such as powder flow ability, reactivity, porosity, density, caking
tendencies, and friability and segregation behaviour (Allen, 1997).

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Particle shape is an extremely complex property to be measured. Several efforts
have been made to measure this property but it shows different dimensional
response to different measuring techniques. It can be described in terms of
“proportions” and “shape factor”.
Proportion distinguishes one shape from another of the same form.
Form refers to the degree to which a particle approaches some standard such as a
sphere, cube or tetrahedron. Some of the common shape factors are:
i. Volume shape factors
ii. Surface shape factors
iii. Aerodynamic shape factors
A simple form of shape factor is the sphericity (0<Φ<1):
Φ = dv/ ds
Where: dv = diameter of a sphere with same volume as the particle
ds = diameter of a sphere with same surface area as the particle
The sphericity of a particle give the measure of how close to being a sphere that
particle is; but it is not definitive especially for irregular shapes (Allen, 1997).
Sphericity of the most materials is in the range 0.65 to 1.
Table 2.1 Particle sphericity (Lettieri, 2009)
Common materials Sphericity Φ
Crushed coal 0.75
Curshed sand-stone 0.8-0.9
Sand 0.75
Crushed glass 0.65
Wheat 0.85
Common salt 0.84

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There are also mathematical expressions to define the shape of a particle but they
are fairly uncommon due to their complexity.
2.1.2. PARTICLE SIZE
Particle size is one of the most factors when considering particle sizing.
Investigations with different powders over the years have shown that particle shape
and size affect many chemical and physical properties. They have a size distribution,
which may be determined using different techniques likes sieving etc. Particle size
can easily be defined for regular shaped particles like spheres on the basis of their
diameter or length. However, for non-spherical or irregular shaped particles, some
form principles of equivalence, particularly equivalent diameter is used to define the
size of irregular shape.
2.1.2.1. Particle equivalent diameter
Following are some of the equivalent diameters used in microscopic analysis of the
particles.
2.1.2.1.1. Statistical diameters
These diameters calculate the linear dimension with respect to defined direction.
Following are some of the statistical diameters:
 Martin’s diameter (d M ): It’s the line that bisects the particle.
 Feret’s diameter (dF):Mean value of the distance between two parallel
tangents on the opposite side of the particle.

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 Unrolled diameter(dR):The mean chord length through the centre of gravity
of the particle
 Image shear diameter (dS h): Width of the particle obtained with an image
shearing device.
 Maximum chord diameter: The maximum length of a line limited by the
particle contour (Arai, 1996; Allen, 1997; Rhodes, 2
2.1.3. PARTICLE SIZE DISTRIBUTION
A particle size density function can be described in terms of either the mass of
particles or the number of particles within a given size range (Fan et el., 1998).
PSD can also be described as a list of values shown as frequency distribution curves
or cumulative curves (Rhodes, 2008). The PSD is obtained by measuring the number
or weight of the particles contained in each size class. The knowledge of PSD is
fundamental in controlling and improving product quality and handling.
The most commonly used ways of expressing the particle size distribution are:
 Cumulative distribution
 Frequency distribution
2.1.3.1. Cumulative distribution
A cumulative distribution shows the ratio of the number of particles greater or
smaller than the size of each class to the total number of all the particles measured
in cumulative analysis. The cumulative analysis is used where the amount undersize
or oversized particles are concerned. The ratio can be in fractions, percentages by
mass or volume. An example of cumulative distribution is shown in the table 2.1.

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Table 2.1: Cumulative size distribution in terms of mass
Perhaps the best way to show the cumulative analysis is not in a table form but
instead is represented as a figure such as figure 2.1 below.
Figure 2.1: Cumulative mass% size distributions
Diameter range
(μm)
Mass(g) %mass % Cumulative mass
0-212 1.74 1.6% 1.6%
212-300 19.26 18.2% 19.8%
300-425 34.21 32.3% 52.1%
425-500 15.02 14.2% 66.3%
500-600 12.26 11.6% 77.9%
600-710 11.46 10.8% 88.7%
710-850 9.84 9.3% 98%
850-1000 2.2 2.1% 100%

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2.1.3.2. Frequency distribution
A frequency distribution shows the ratio of the number of particles greater or
smaller than the size of each class to the total number of all the particles measured
in range analysis.
Figure 2.2: Frequency distribution histogram
2.1.4. PARTICLE DENSITY
The density of a particle immersed in a fluid is defined as :
Particle density, ρp=M / Vp
Where: M is the mass of the particle
Vp is the hydrodynamic volume “seen” by the fluid in its fluid dynamic
interaction with the particle, it includes the volumeof all open and closed
pores (Lettieri , 2009).

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2.1.4.1 Absolute density
For non-porous solids the particle density equals the skeletal or absolute density,
ρp=ρABS:
ρABS = M/V sm
where: M = mass of the particle
Vsm = volume of solids material making up the particle mass of particle
Figure 2.3 Particle density
For porous solids, ρp<ρABS
A mercury porosimetry analysis can be used to measure the density for coarse
porous particles (Lettieri , 2009).
2.1.4.2. Bulk Density
Another term used in connection with fluidized beds is the bulk density, which
includes the voids between the particles. Given below is the equation for bulk
density:

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Bulk density, ρb = M/VT
where: M = mass of the particles in the bed
Vsm = total volume which includes the volume occupied by the particles and
the void volume.
Bulk density is related to particle density and bed voidage as follows:
ρb = (1-ε) ρp
(Lettieri, 2009).
2.2. SAMPLING
The analysis of a particular sample of particles is for any purpose depends on how
that sample represents the bulk. In practise, a few grams of sample are obtained
from many tonnes. The chances of measuring a representative few grams out of
tonnes of powder are very slim(Allen, 1997). This is precisely why, the sampling is
carried out. Sampling is a very important step in PSD as obtaining true representative
sample of the bulk is critical. Some of the methods of sampling are:
2.2.1. CONING AND QUARTERING
This is arguable the most effective way of sampling. This technique is suitable for
non-flowing or cohesive powders. In this method, the powder is poured into a
conical heap which is then flattened as evenly as possible by a cross shaped cutter.
This material is then divided into quarters where two opposite quarters are
discarded. The remaining two quarters recombined and poured into another conical
pile which is flattened and divided again. The above process is repeated until we are
left with our desired sample. The accuracy and precision in this method relies on the
radial symmetry of conical heap.

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2.2.2. SCOOP SAMPLING
This is the simplest method of sampling but by no means as effective. In this method,
a scoop is dipped into the surface of a powder to collect a sample. The sample taken
through this method is not representative of the entire powder at all as the whole
sample doesn’t go through the sampling device unlike quartering.
2.2.3. TABLE SAMPLING
This technique involves the use of a sampling table whose top is inclined with series
of holes. It consists of prisms placed in the path of the flowing powder to break into
fractions. Any powder that falls through the holes is disposed while the remaining
powder passes on to the next row of holes and prisms to remove more. The process
continues until the representative sample of the powder gets to the bottom.
2.2.4. CHUTE SAMPLING
This method of sampling involves the bulk powder passing through a funnel shaped
trough. The trough has number of chutes along the bottom of it. These chutes
alternately are feeding two trays which are positioned either side of the trough. The
bulk powder is continually divided into both trays until the desired representative
sample is obtained (Allen 1997).
2.2.5. SPIN RIFFLING METHOD
This method generates samples of particulates which reflect very closely the
properties of the larger quantity from which they were derived. The composition of
a sample produced by spin riffling usually approximates very closely to the
theoretical limits imposed by the statistical functions by which that material is best
described.

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The spin riffling technique relies on the concept of random sampling to build a set of
fractions from a bulk of material so that each fraction contains all the
characteristics, including particle size distribution, as the bulk from which they all
came.
A spinning riffler comprises three principal components:
 A Mass Flow Hopper which holds the bulk of particulate to be sampled;
 A controlled–rate Feeder which steadily transports the bulk from the
Hopper to the Sample Collectors;
 A Dividing Head placed on a rotating platform above the Collectors or
integral with them, which cuts the particulate stream from the Feeder into
small incremental portions, repeatedly.
Since the device is designed to allow many passes of the Dividing Head during the
course of one sampling operation, each fraction is built up from multiple samples of
the bulk. So long as the Dividing Head rotation and the flow of particulates along the
Feeder are both constant, the fractions which accumulate in the Sample Collectors
during the riffle will be closely representative of the bulk. (Hawkins, A. E., 1988, L. A.
Kressin, Powder and Bulk Engineering, July 1989, Allen, T. and Khan, A. A., 1970)
Simple Comparison
Table 2.2: Standard Deviations of the samples % (Allen, T. and Khan, A. A., 1970)
Coning and quartering 6.81
Scoop sampling 5.14
Table sampling 2.09
Chute sampling 1.01
Spin riffling 0.125
Random variation 0.076

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"Spin riffling has been shown to be the most accurate and reliable technique for the
representative sampling of particulates." Dr. Arthur Hawkins, 1996.
"The real benefit in spinning is repeatable test results that are reliable. You save time,
resources, material, and ultimately money." Alan Gibbon, Johnson Matthey, 1992.
"The spinning riffler is the best technique by far – it samples unmixed just as
efficiently as mixed powders." T. Allen and A.A. Khan, 1970.
"Extensive studies have shown spin riffling to be a very efficient sampling method."
Brian Kaye, 1981.
Hence we can conclude that spinning riffler produces the best representative sample
in the bulk powder and that it would be the most suitable technique to sample our
particulates for analysis or sizing.
2.3. PARTICLE SIZE MEASUREMENT TECHNIQUES
The importance of particle sizing could be seen by the fact the 30% of the world’s
chemicals are in powder ( T.Allen, 1996).
Pharmaceutical and cement industries are heavily dependent on the effective
particle sizing as it is a key factor in the quality of the finished product. As the result
of this importance of particle sizing, many techniques have been developed to the
date for this purpose. The techniques used for particle size analysis involve both
classicaland modern instrumentations, based on different physical principles.

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Table 2.3: Different particle size distribution techniques
2.3.4. SIEVING
Sieving is the oldest means of particle separation and most widely used powder
classification. The two main reasons for this technique to be the most widely used
even in this age are:
 Simplicity
 Low cost
It is also independent of some particle properties like density, surface roughness and
optical properties. In this method the particles to be measured are classified into
different sizes by a series of five to 10 sieves with different holes diameter
depending on the object of measurement. The size distribution is then calculated
from the weight ratio of the particles on each sieve. This method does have a
comparatively large measurement error which is because of the adhesion to the
sieves and cohesion between particles. This error is more so in finer particles (Allen,
1997; Lettieri, 2009; Arai, 1996; Rhodes, 2008).
Technique of sizing Method of operation
Sieving Mechanical
Sedimentation Dynamic
Microscopy Electronic , Optical
Impaction Dynamic
Laser diffraction Electronic, Optical
Adsorption Physical, Chemical

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2.3.2. SEDIMENTATION
Sedimentation is another very old and fairly useful technique for particle sizing. This
method determines the rate at which the particles settle through a fluid(mostly
liquid) of density less than that of the particles.
Sedimentation could be done in mainly two ways:
 Gravitational Sedimentation
 Centrifugal Sedimentation
2.3.2.1. GRAVITATIONAL SEDIMENTATION
This method makes use of the terminal velocity obtained by particles suspended in a
viscous liquid. These particles travel through the liquid under gravity and settle at
the bottom. Typical apparatus disperses the sample in liquid and then measure the
optical density of the layers of particles settled using visible light or soft x-rays. The
lower limit of particle sizing using gravitational sedimentation is about 10 microns.
This is effected by Brownian motion, diffusion, convection etc.(T.Allen, 1997;Yang,
2003).
2.3.2.2. CENTRIFUGAL SEDIMENTATION
In this method, the relative size distributions of the particles are measured
separation in a field of centrifugal force. The relative concentration of the particles at
any single point is measured, usually by light absorption methods, and the relative
size is calculated from the time and distance travelled of the particle. This method is
useful for wide size distributions but has flaws in shape and density variations
(Allen,1997; Coulson et el, 1999; Rhodes, 2008).

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2.3.3. MICROSCOPY
This method is often regarding as the best method for particle sizing due its direct
visualization and measurement of an individual particle. It is the one and only
method to do so. This technique is normally used for sizing of very few particles
because it is time consuming to do microscopy of large number of particles. In using
those few particles, there is a massive chance of unrepresentative sampling and if
the weight distribution is measured results are magnified. If we could somehow
make sure that our sampling is representative, microscopy is easily the most
convenient method around. Three commonly used types are optical microscopy,
transmission electron microscopy (TEM) and scanning electron microscopy (SEM).
2.3.3.1. OPTICAL MICROSCOPY
This is the oldest of microscopy techniques. This technique is very useful and
accurate in obtaining the shape and size (down to 5 microns) of a particle. However,
the things like particle density etc. cannot be obtained using microscopy.
Microscopes being fairly inexpensive make this technique very common as well.
Applying adhesive to the microscope ensures that particles are randomly orientated.
(Yang, 2003;T.Allen, 1996).
2.3.3.2. TRANSMISSION ELECTRON MICROSCOPY (TEM)
This relatively new technique is very effective for finer(sub-micron) particles. In this
method, a beam of electrons is transmitted through a layer of particles with very
small size (below 5 microns). As electrons pass through the particles they interact
with the particles. An image is formed from the interaction of the electrons
transmitted through the layer of particles; the image is magnified and focused onto
an imaging device, such as a fluorescent screen, on a layer of photographic film, or to

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be detected by a sensor such as a CCD camera. (Hawkes, P. ,1985;Yang, 2003;T.Allen,
1997).
Figure 2.3 An image of particles using TEM showing their size and shapes.
2.3.3.3. SCANNING ELECTRON MICROSCOPY (SEM)
SEM works in the similar fashion to that of TEM. SEM is used to examine the fine
details of material structures. Particle size standards can be used to check the
accuracy of particle sizing done by SEM. This technique can successfully size down to
as much as 0.8 microns.
2.3.4. LASER DIFFRACTION METHOD
Laser diffraction, alternatively referred to as Low Angle Laser Light Scattering (LALLS),
can be used for the non-destructive analysis of wet or dry samples, with particles in
the size range 0.02 to 2000 micron and has inherent advantages which make it
preferable to other options for many different materials.The fundamentals of this
technique lie in the relation of diffraction angle to the particle size . Diffraction angle
is inversely proportional to the particle size.
In laser diffraction particle size analysis, a representative cloud of particles passes
through a broadened beam of laser light which scatters the incident light onto a

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Fourier lens. This lens focuses the scattered light onto a detector array and, using an
inversion algorithm, a particle size distribution is inferred from the collected
diffracted light data. Sizing particles using this technique depends upon accurate,
reproducible, high resolution light scatter measurements to ensure full
characterizations of the sample.(Rhodes, 2008; Yang 2003;T.Allen, 1997; Allen, 1990).
2.4. SPRING SIZE MEASUREMENT TECHNIQUE AND DEVELOPMENT
The spring size analyser is a novel technique, invented by the department of
chemical engineering, university college London. This technique overcomes the
certain limitations and drawbacks associated with the previously developed
techniques for particle size measurement.
2.4.1. BASIC PRINCIPLES OF OPERATION
The basic principle of operation involve the instrument comprises a closed coil
helical spring which is filled with the sample of wide range of powdered particles of
different size. When the spring is stretched, the gaps between the coils allow the
particles with smaller diameter, to escape. Similarly, when the spring is stretched
more, larger particles are allowed to discharge. Thus the sample is separated into
different size fractions and weighed to produce particle size distribution. This
mechanism is shown in Figure 2.4.
Figure 2.4: Representation of spring extension mechanism.

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2.4.2. VIBRO-SPRING PARTICLE SIZER METHOD (MARK I)
This novel method was developed by Mahgerefteh and Shaeri in 1996. This
technique is based upon a closed coil helical spring. The unit was also named as
MARK I. In this particular analyser, the spring (1) is set up horizontally and is partially
filled with a test sample. One end of the spring is securely attached to one side of
the main chamber (2) whilst the other end is permanently sealed. The sealed end is
attached to a 100 mm long 12 BA screw (3) by a positioning plate (4) on the other
end. The positioning plate is mounted on two slide rails (5,6).
Figure 2.5: Schematic diagram of Vibro-Spring Particle Size Analyser (MARK I)
(1) Spring
(2) Main chamber
(3) BA screw
(4) Wire plate
(5) 1st Side rail
(6) 2nd Side rail
(7) Feed elbow (Funnel)

28
(8) Vibrator generator
(9) Glass containers
The process begins by feeding a sample through the feed elbow (funnel)
(7). A computer controlled stepper motor is used to stretch the spring and a vibrator
generator (8) is used to vibrate the spring vertically. Particles that come out of the
stretched and vibrating spring are collected at collectors (9). Collected particles are
weighed using a conventional balance (Shaeri, 1997).
Amongst several advantages, there are some limitations in MARK I. one of the most
obvious ones, was the lack of built in measurement devices. For instance, the
particles which are collected at collectors (9), are to be removed and weighed
manually. The vertical vibration of the spring causes the non-uniformity of the spring
coil openings. This non-uniformity resulted in some of parts of the spring more open
than others, allowing larger particles to discharge earlier than they are suppose
to(Kerdvibulvech, 2008).
Figure 2.6: Photograph of Vibro-Spring Particle Size Analyser (MARK I)

29
2.4.3. MODIFIED VIBRO-SPRING PARTICLE SIZER (MARK II)
MARK II was developed to overcome the problems in the MARK I. MARK II was
developed by Patel (2001). This was based on same principles as MARK I but the fact
that it had potential for in-situ and continuous measurement of the mass of the
representative powder within the spring was the key. In addition to that, in MARK II
the spring could be extended from both sides which ensured even extension of the
coils.
Figure 2.7: A Schematic diagram of the modified Vibro-Spring Particle Size Analyser
(MARK II)
(1) Spring
(2) Rectangular bars
(3) Control screw
(4) Stepper motor
1
2
6
4
5
9
8
10
3
7
15
14
13
16
12
17
11
18

30
(5) Wire connection
(6) Control disk
(7) Funnel
(8) T-piece
(9) Support frame
(10)Steel disk
(11) Electro-magnet
(12) Spring steel reed
(13) Reed support block
(14) Base plate
(15) Infrared detector
(16) Detector support legs
(17) Base support legs
(18) Pivots
Figure 2.8: A PHOTOGRAPH OF THE VIBRO-SPRING PARTICLE SIZER DEVELOPED BY
SHAERI (1997)

31
The figure 2.6 is the schematic diagramof MARK II, developed by Patel (2001). The
instrument comprised a closed coil helical spring (1) supported horizontally at each
end by two rectangular cross-sectional aluminium bars (2). One end of each bar is
mounted with the spring whilst the other end is attached to a control screw (3). The
control screw is threaded at each end. The winding and unwinding of the control
screw takes place via flexible wire connection (5) with a computer controlled stepper
motor (4). The stepper motor is directed to move the two aluminium bars inwards or
outward, resulting in closing or opening the spring respectively. The system can also
be operated manually. This is done by winding or unwinding control screw manually
by turning a centrally positioned control disc (Patel, 2001).
The test sample is poured into the spring through a plastic funnel mounted at one of
the spring. The two bars (2) are held in the same horizontal plane during vibration by
passing through a specially constructed T- shaped piece (8). One end of the T-shaped
piece is attached to main supporting frame (9) by means of pivots where as the
other end L-shaped end is mounted on the mild steel disc (10) to allow magnetic flux
linkage with the electro-magnet (11). The electro-magnet is used to drive the system
into transverse vibration. The distance between the steel disc and electro-magnet is
approximately 4mm. Resistance to lateral vibration is offered by a 1 mm thick
rectangular spring steel reed (12). One end of the steel reed is attached to the T-
piece whilst the other end is firmly clamped to the aluminium supporting block (13).
The effective length of the reed is controlled by sliding the supporting block along
the grooved base plate (14). The vibration of the reed is detected by an infrared
detector (15) supported on sliding block (16). The entire systemis supported on four
cylindrical legs (17) (Patel, 2001).

32
Figure 2.9: Schematic representation of the SPS capacitance transducer- cantilever
mass measurement technique
(1) Transducer
(2) Aluminium supporting block
(3) Sensing arm
(4) Spring
(5) Reed clamp
(6) Pivot
(7) Spring steel hinge
(8) Supporting block
(9) Vibrating reed
10) steel ball bearing
The discharged particle size and its mass are determined from spring extension and a
especially designed in-situ cantilever mechanism respectively. MARK II could carry
out particle size distribution of the particles ranging 30-1200 μm. Also the tests
which included glass ballotini particles favourable results compare to sieve (Patel,
2001).
MARK II had improved remarkably from MARK I. Some of the facts showing that are
extension in spring without in tension in the reed. There was significant reduction in
the analysis time. As mentioned earlier, it had in-situ mass measurement. Besides all
that, MARK II did have some drawbacks. For instance, it was incapable of handling
more 10g of a sample which is very unlikely to be representative of a large sample

33
for large scale industrial processes. It had limited range of size measurements and
operation difficulties with cohesive samples. There is also the wear and tear of the
gears used for automatic extension of spring (Kerdvibulvech, 2008).
2.4.4. HAND-HELD PARTICLE SIZE ANALYSER METHOD
Hand-held spring particle size analyser was developed under the same basic
principles as MARK I, I, III however the agitation is in this analyser is done manually
by shaking the device. The equipment operates by turning the top cap in anti-
clockwise direction to extend t spring. The bottom part of the spring fixed and this is
where the particles are fed into the spring. Once the particles are inside the spring,
the whole equipment is shook to agitate the particles; which as a result are
discharged depending upon the aperture size. The discharged particles are collected
in the Perspex particle collector for measurement and to obtain particle size
distribution (Kerdvibulvech, 2008).

34
Figure 2.10: Photograph of the Hand-held Particle Size Analyser with Calibrated
Perspex Particle Collector
The hand-held analyser is extremely simple and is capable of analysing reasonable
amount of test sample. It is relatively inexpensive and also has very low maintenance
cost. It is fairly robust and can be used to readily monitor particle size distribution.

35
CHAPTER 3| APPARATUS ANDDETAILS OF MARK III
3.1. PNEUMATIC SPRING PARTICLE SIZER (MARK III)
This particle size analyzer was developed by Mahgerefteh and Kamugasha (2004) in
order to overcome the various problems associated with MARK I and MARK II.
MARK III was fundamentally based on same principles. However, in MARK III the
helical spring was set up in a vertical position and was extended from one end.
Pressurised air was used to agitate the particles in the spring. Use of pressurised air
meant that no more vibration of the spring was required and thus no coil deflection.
The spring is stretched by means of a screw mechanism which works in alignment
with stepper motor. This device had the capability to carry out thr particle size
distribution of particles in the range of 30-2000 µm (Mahgerefteh and Kamugasha,
2004).
Figure 2.9 represents the detailed schematic diagram of the MARK III. The feed
hopper (1) is mounted on a feed plate (2). The top end of the spring is fixed to the
feed plate using a spring connector (4). The bottom end of the spring is inserted and
tightened into the top of a conical base holder (5). The conical base holder also
supports the air inlet channel (6) and mesh screen(7). The mesh screen acts as a
distributor plate to the particles. Particles cannot pass through the mesh screen but
the air can. The bottom of conical base holder (5) is connected to a spring extension
screw (8) which is used to extend the spring for desired aperture size. The spring
extension screws along with a hollow aluminium tube (9) are boxed in a telescopic
enclosure (10). The telescopic enclosure prevents the extension screw from getting
any sort of damage by test powders.

36
Figure 3.1: Schematic diagram of Pneumatic SPS (MARK III)
AIR
AIR
AIR
(1)
(2)(4)
(3)
(6)
(7)
(9)
(11)
(12)
(13)
(16)
(17)
(18)
(15)
(8)
(5
)
(14)
(10)

37
The aluminium tube connects the extension screw indirectly to the shaft of the
stepper motor (11) which is responsible for extension and compression of the spring.
The shaft encoder (12) monitors the spring extension which is coupled to the rear
end of the stepper motor and is housed in a cylindrical aluminium container (13).
The whole assembly is mounted onto a supporting base (14) via three aluminium
rods (15). The supporting base also supports the feed plate (2) by means of three
different aluminium rods (16) which are set up as a tripod. The whole system is
boxed in a cylindrical enclosure.
Pressurised air is sent through the mesh screen (7) which acts a plate to the particles.
Once the spring is extended at a desired aperture size, the agitating particles start
discharging depending upon the diameters of those particles. The powdered
discharged from the spring is directed towards a machined outlet orifice (18) located
at the bottom of the base.
The control software to control this device is HP VEE (Hewlett Packard Visual
Engineering Environment). The HP VEE is a visual programming language used to
program tasks in instrument control, measurement processing and test reporting. It
helps linking graphical objects into block diagrams to represent a program
(Kerdvibulvech, 2008).
Once the particles are discharged, they are weighed using a weight mechanism
which place and clamped at the bottom of the systemand right underneath outlet
orifice. This is shown in figure 2.10 and 2.11.

38
Figure 3.2: Schematic Diagram of the weighing mechanism with filter cloth and
solenoids
3
6
4
5
1
2
1
2
3
4
6
5

39
(a) (b)
Figure 3.3: Detailed Diagram of the weighing mechanism showing; Clamping (a)
and Unclamping (b)
2
1
3
4
6
5
2
1
3
6
5
4
7
9
8
71

40
CHAPTER 4| RESULTS AND EVALUATION OF MARK III
In this chapter, performance of Pneumatic SPS (MARK III) is evaluated by discussing
series of results obtained by performing different experiments. This will include
looking at:
 Comparison with data obtained by sieves.
 Constant air pressures with changing air pulse rate for the particles ranging
250-1180 μm.
 MARK III acting as fluidised bed and its behaviour for different range of
particles.
 Comparing data obtained using newly installed digital calibre to measure the
height with the old way of measuring height.

41
4.1. COMPARISON WITH SIEVE DATA
Figure 4.1 shows the PSD data and cumulative trend for an experiment conducted on
a powder sample of 20g of mixed glass ballotini in the size range of 180-1000 μm.
The experiment to get the PSD data in figure 4.1 was conducted on the same sample
of glass ballotini. The PSD data is used to compare the performances of sieve method
and pneumatic spring particle size analyzer (MARK III). The PSD data for MARK III in
the figure 4.1 was obtained using air pressure of 15 Psi.
Figure 4.1: PSD data of 20g sample of glass ballotni in size range of 180-1000 μm.
It can be seen from figure 4.1, that the cumulative undersize curve of sieve data has
more linear look to it. This is because of the non-spherical particles in the size range.
These non-spherical particles are able to pass through the spring coils in MARK III but
they are unable to pass through the sieve of same diameter. This is explained with
the help of figure 4a.
If the particle shown in figure 4a is in a sieve, it is likely to stay there as sieve
measures larger dimension due to its square apertures. Whereas the MARK III
measures the smallest dimension of the particle due to spring having slotted
apertures.
0
10
20
30
40
50
60
70
80
90
0 200 400 600 800 1000
Cumulativeundersize(%)
mean particle size (μm)
spring data
sieve data

42
Another noticeable factor in figure 4.1 is that, approximately 81% of the initial 20g
sample was retrieved using MARK III which gives 19% of the sample lost to errors.
Whereas using sieve, approximately 78% was obtained which addresses 22% of the
particles loss to error in sieves compare with MARK III.
The fact that MARK III has slotted apertures is equally disadvantageous, as some of
the particles with larger diameter would pass through the slotted aperture at its
smallest dimension.
Figure 4a: Irregular shaped particle with multiple dimensions
The reproducibility of spring data from MARK III and sieve data is shown in figure 4.2
and 4.3 respectively. The 20g sample, for all the sets of readings was obtained by
dividing an 80g mixed sample of glass ballotini into four identical cuts.
Figure 4.2: MARK III PSD data reproduciblity
0
10
20
30
40
50
60
70
80
90
0 200 400 600 800 1000
spring data, 1st run
spring data, 2nd run
Smallest dimension
Larger dimension

43
Figure 4.3: Sieve PSD data reproduciblity
4.2. AIR PULSE RATE AND PARTICLE SIZE RANGES
This section illustrates a series of experiments carried out in order to work out the
most suitable combination of operating parameters such as pulse rate and to
evaluate the performance of MARK III for different particle sizes.
This section is divided into two sub-sections. First sub section involves varying the
particle size ranges for each pulse rate. The other section consists of experiments for
varying the pulse rate for each range of particle size.
4.2.1. DIFFERENT PARTICLE SIZE RANGES AT CONSTANT P.R
In this section, numbers of experiments were carried out for particle size ranges
180-250, 250-355, 850-1000 and 1000-1180. Tests on 5g of each of the above
particle sizes are conducted separately. They are not mixed. However, firstly, the
0
10
20
30
40
50
60
70
80
90
0 200 400 600 800 1000
'sieve data, 1st run
sieve data, 2nd run

44
number of steps by which the spring is extended, is worked out for each of the above
size ranges. This is done as follows:
final height = initial height − [
average diameter×number of active spring coils
104 ]
where;
Final height = length of the spring after extension
Initial height = length of the spring before extension (actual length of the spring)
Average diameter = mean particle diameter (215 for the range 180-250)
Number of active spring coils = spring coils that are able to extend (54 for the spring
in MARK III)
Calculations for the range 180-250 μm:
final height = 24.5 − [
215×54
104 ]
final height = 23.3 cm
final height − initial height = 24.5 − 23.3
final height − initial height = 1.2 cm
Approximately,
0.20cm of spring length = 200 steps
⇒ 1.20cm =
200
0.2
steps
⇒ 1.20cm = 1000 steps
⇒ at 23.30cm = 1000 step

45
Hence, the spring was extended by 1000 steps for the particle size range of 180-250,
the MARK III was operated at constant pulse rate of 0.5 seconds per cycle.
Similarly, the number of steps for spring extension at which for the size ranges 250-
355, 850-1000 and 1000-1180 are calculated.
Steps for the range 250-355 μm:
Final height = 22.9 cm
⇒ at 22.9 cm = 1600 steps
⇒ at 19.5cm = 5000 steps
⇒ at 18.6 cm = 5800 steps
The figure 4.4 shows the PSD data for 180-250, 250-355, 850-1000 and 1000-1180at
pulse rate of 0.5 seconds per cycle. In the figure, cumulative mass is plotted against
the number of time steps. Each time step is equal to one minute (60 seconds). This
can also be calculated as follows;
one time step = P. D × P. R × 2
where;
Time step = time taken to discharge the particles (seconds) or (minutes)
P.D = Pulse duration (cycles)
P.R = Pulse rate (seconds/ cycles)

46
Calculation of time step at P.D = 60, P.R = 0.5 :
one time step = 60cycles × 0.5
seconds
cycle
× 2
one time step = 60 seconds
one time step = 1 minute
Hence, plot of cumulative mass discharge against number of time steps gives an
indication how quickly MARK III can discharge particles.
Figure 4.4: PSD data of 5g sample of glass ballotini in the size range of 180- 1180μm
obtained at constant pressure and at P.D = 60 and P.R =0.5
It can be seen from figure 4.4 that, although particles discharged quicker for 180-250,
the PSD for that size is range is far from smooth and accurate. PSDs for other three
particle size ranges show very smooth trend and accurate discharge of particles.
However, for 850-1000 and 1000-1180, particles are discharged after longer period
of time. This leaves the size range of 250-355 which is discharged (after 8 time steps)
almost as quickly as 180-250 and it has smooth trend and accurate discharge.
Another important factor to be looked at is that how much of the particles are
discharged. Figure 4.4 shows that almost all the curves representing size ranges
ended up discharging more than 4.5g which is more than 90%.

47
Figure 4.5: PSD data of 5g sample of glass ballotini in the size range of 180- 1180μm
obtained at constant pressure and at P.D = 30 and P.R =1
Figure 4.5 shows a similar trend to that of figure 4.4, apart from the fact that less
than 90% of the 250-355 is discharged which is a lot less than other size ranges.
Also, the size range 180-250 is discharged quicker than in figure 4.4.
Figure 4.6: PSD data of 5g sample of glass ballotini in the size range of 180-
1180μm obtained at constant pressure and at P.D = 0.5 and P.R =60

48
Again, the trend in figure 4.6 is of the similar manner to figure 4.4 and 4.5.
It can be noticed from figure 4.4, 4.5 and 4.6 that, as the particle size increases the
MARK III takes longer to discharge them. Also, as the size range increases more of
the particles are discharged. In other words, fewer particles are lost within the
apparatus as the size range increases.
The particle size range of 180-250 does not seemto follow the second trend as more
particles this range is discharged than the size range 250-355. This is mainly because
of instrument (weighing balance) and human error.
4.2.2. CHANGING PULSE FOR SAME PARTICLE SIZE RANGE
In this section, the pulse rate is varied and its effects, on different particles size
ranges, are noted. The particle size ranges used in this section are; 180-250, 250-355,
850-1000 and 1000-1180.
The figure 4.7 shows the PSD data of cumulative mass against time steps for the size
range of 180-250 at different pulse rates of 0.5, 1, 60 seconds per cycle. To conduct
this test 5g sample of glass ballotini was used.
Figure 4.7: PSD data of 5g sample of glass ballotini obtained for different pulse
rates for the size range of 180-250 at constant pressure

49
All curves in figure 4.7 shows that as pulse rate increases, the particles are
discharged quicker. This makes sense because at higher pulse rate, the pressurised
air is in contact with the particles for longer period of time. There was no clear
finding of how pulse rate affects the percentage of particles discharged from the
figure 4.7. Nonetheless, all the pulse rates discharge more than 4.5g (90%) of
particles.
Hence for particles ranging 180-250 μm, the pulse rate of 1 seconds per cycle would
be best as it discharges the most particles and in less time.
The figure 4.8 shows that 60 seconds per cycle is the best pulse rate for particle size
range of 250-355 μm. This is due the fact that almost 95% of the particles are
discharged.
Although, the particles do not discharge at the quickest rate at this pulse rate, it is
still quicker than pulse rate of 0.5.
The figure 4.9 implies that pulse rates of 1 and 60 seconds per cycle, are discharging
the particles ranging between 850 and 1000 in almost same amount and taking same
time to discharge them.

50
However the PSD curve for pulse rate of 1 seconds per cycle is has smoother trend
and hence the accurate particle size distribution.
Figure 4.10 is very similar to figure 4.9. It shows that pulse rate of 1 second per
cycles will be best for this size range.

51
The figures 4.7to 4.10 show same trend as far as time to discharge the particles is
concerned. However nothing is conclusively is shown by PSD curves on mass or
percentage of particles discharged.
It could be concluded that pulse rate has no effect on discharged mass of particles.
This because the particles are lost to different parts of instrument whether or not
pulse rate it
Also, it can be concluded from the trend that the particles with smaller diameter are
discharged earlier but more percentage of larger particles is discharged.
The reproducibility of the data in the figures 4.4 to 4.10 can be seen in the Appendix
A1.
4.3. FLUIDISATION
The set of experiments in section 4.3 are based the principle of fluidisation using
various sample masses of glass ballotini. The experiments were to be conducted for
particles ranging 212-300, 300-425, 500-600 and 710-800. This set of size ranges
were chosen in order to get results for diverse set of particle sizes. However due to
inconclusive evidence, a further set of experiments were conducted for the particle
size range of 425-500. All these experiments were performed for 5, 10, 20, 50 and
100g mass sample of glass ballotini for all the above size ranges.
Figure 4.10 shows general trend of pressure drop for increasing and decreasing the
air flow rate in MARK III compared with standard fluidised bed.

52
Figure 4b: Variation of pressure drop with increase and decrease in flowrate
4.3.1. FLUIDISATION AT DIFFERENT MASSES AND PARTICLE SIZES
In this set of experiments, the data collected was plotted as pressure drop against
flowrate of air. This is to ascertain if there is a relationship between mass of the
particles and pressure drop as well as a relationship between particles masses with
minimum fluidisation.
The figure 4.11 shows the varying pressure drop and flow rate for 5 to 100g sample
masses of 212-300 μm of glass ballotini. It is clearly visible from the figure 4.11 that
lower masses have lower pressure drop. As the mass increases the pressure drop
increases.
0
10
20
30
40
50
60
0 50 100 150 200
Pressurechange,KPa
Air flowrate, litres/min
standard fluidised bed
increasing flow rate
decreasing flow rate

53
Figure 4.11: Pressure drop against increasing flowrate with sample masses of
212-300 μm glass ballotini
The minimum fluidisation for the masses ranging 5g to 50g is in the range of 60 to
85 litres min-1. The 100g of 212-300 μm is not fluidised. The reason being 100g of
that size of particles would have less voidage for air to fluidised it.

54
The figure 4.12 shows the varying pressure drop and flow rate for 5 to 100g sample
masses of 300-425 μm of glass ballotini. Figure 4.12 illustrates that although
pressure drop increases with increase in particle mass but the increases for size
range of 300-425, are not as big as the particles ranging 212-300 as shown in figure
4.11 .
Unlike last range of sizes, the minimum fluidisation is almost exact 60 litres min-1 for
all the masses ranging 5g to 50g . The 100g of 300-425 shows same trend as 100g of
212-300.
The figure 4.13 describes the variation in pressure drop and flow rate for 5 to 100g
sample masses of 500-600 μm of glass ballotini. Figure 4.13 validates the same
pattern of increasing pressure drop with increase in masses. However, for this range
of particles, 100g shows the same pattern as other masses unlike previous two
ranges. Although the increase in pressure drop for 100g is slightly more than the
other masses.

55
According to figure 4.13, the minimum fluidisation for all the masses in range takes
place at about 70 litres min-1. Unlike last two size ranges, the 100g of 500-600 was
fluidised as well.
The figure 4.14 describes the variation in pressure drop and flow rate for 5 to 100g
sample masses of 710-850 μm of glass ballotini. Figure 4.14 shows almost exact
same trend as figure 4.13.
The only minor difference is that minimum fluidisation occurs at relatively different
air flowrate for different masses which is unlike in figure 4.13. The minimum
fluidisation range is 60 to 70 litres min-1.

56
Figures 4.11 to 4.14 show the variations in the pressure drop and minimum
fluidisation for different masses of 212-300, 300-425, 500-600 and 710-850 μm.
So far, the trend for variations in pressure drop has been same for all the above size
ranges but as far as minimum fluidization is concerned the trend for 212-300 and
300-425 has been similar, where there was no minimum fluidisation for 100g. This
has been different for the size ranges of 500-600 and 710-850 where there was
minimum fluidisation for 100g. Hence, the experiments had to be conducted on an
intermediate particle size range (425-500 μm) in order conclude of dilemma of 100g
minimum fluidisation.
The results of the experiments conducted on 425-500 were truly astonishing as
shown in the figure 4.15 below. Three runs were conducted, instead of normal two
runs, for 100g 425-500 and reproducibility of it is shown in figure 4c.
Incredibly, the figure 4.15 shows two minimum fluidisation points for 100g. The first
one occurs in the region of 40 to 50 litres min-1 whereas the second minimum

57
fluidisation happens at about 100 litres min-1. Also, when the experiment was being
carried out for 100g of 425-500, it was noticed that sound inside the spring of MARK
III, was somewhat different and a lot louder as the flowrates were increased.
This shows that if the air flow rate was increased even more, there would been
minimum fluidisation for 100g of 212-300 and 300-425 μm as well.
Figure 4c: Reproducibility of 100g sample of 425-500 μm of glass ballotini
Also, there was no distinguishing difference between the minimum fluidisation flow
rate for the masses between 5 to 50g. Though the minimum fluidisation for 100g
was distinctive enough, it was very inconsistent for most particle size ranges.
Therefore, this rules out any chance of using minimum fluidisation flowrate to work
out masses of the particles. Similarly mass- pressure drop relationship is fairly
inaccurate for in-situ mass measurements due pressure fluctuations.
Figures 4.16 to 4.20 embody another way of presenting the relationship of pressure
drop and flow rate with masses and sizes of the particles.
0
10
20
30
40
50
60
70
0 50 100 150 200
Pressurechange,KPa
100g, 1st set of readings
100g, 2nd set of readings
100g, 3rd set of readings
Average

58
Figure 4.16: Pressure drop against increasing flowrate for different particle size
ranges of 5g of glass ballotini

59

60
Reproducibility of the data for the figures 4.10 to 4.20 can be found in Appendix A2.
4.4. COMPARISON BETWEEN DIGITAL AND ANALOGUE CALIBRE
Accurate measurement of length (height) of spring in MARK III has always been a
dilemma which has led to the problem not knowing the number of steps for particle
sizes. The relation between length (height) of the spring and number of steps has
already been discussed in the section 4.2.1.
It was discussed that approximately, 0.20cm of spring length = 200 steps.
But according to digital calibre, the 200 steps is equivalent to lower length change as
shown table 4.1 and 4.2.

61
4.4.1. ERROR ANALYSIS
Table 4.2 can be used to conduct an error analysis on two calibres.
Maximm error in digital calibre = biggest length change− smallest length chang
The biggest and smallest length change can be obtained from table 4.2.
Maximum error in digital calibre = 0.193 − 0.125 = 0.068 cm
Maximum % error in digital calibre =
0.068
0.193
= 35.2%
Similarly,
Maximum % error in digital calibre =
0.30−0.10
0.30
= 66.7%
The percentage error in old analogue calibre is almost double the error in newly
installed digital calibre.
It can be seen from figure 4.1 that additional accuracy is provided by the extra
decimal place in digital calibre.

62
Table 4.1: comparison between analogue and digital calibre
Analogue Calibre Digital Calibre Number of steps
0 0 0
0.2 0.127 200
0.4 0.268 400
0.5 0.409 600
0.7 0.534 800
0.9 0.723 1000
1 0.907 1200
1.2 1.08 1400
1.4 1.268 1600
1.6 1.442 1800
1.8 1.623 2000
2 1.801 2200
2.2 1.979 2400
2.4 2.155 2600
2.6 2.331 2800
2.8 2.503 3000
3 2.696 3200
3.2 2.874 3400

63
Table 4.2: comparison of change in length between analogue and digital calibre
Figures related to analogue and digital calibre are in the Appendix A3.
change in length according to digtial calibre change in length according to analogue calibre
0.141 0.2
0.141 0.1
0.125 0.2
0.189 0.2
0.184 0.1
0.173 0.3
0.188 0.1
0.174 0.2
0.181 0.2
0.178 0.1
0.178 0.2
0.176 0.2
0.176 0.3
0.172 0.2
0.193 0.2

64
CHAPTER 5| CONCLUSIONS ANDFUTURE WORK
5.1. CONCLUSIONS
The thesis describes history, development and series of experiments conducted
towards improving and optimizing the performance of the Pneumatic Spring Particle
Size Analyser (MARK III).
The MARK III is primarily developed to perform effective particle size distribution
(PSD) and compete with other conventional techniques for PSD. It is meant be
inexpensive, robust and relatively simpler to operate. It is the latest model in the
evolution of helical extension spring being used as a means for determining PSD. The
PSD data is obtained by the extension of a vertical held spring, through which the
particles of that aperture size discharge. The PSD curve is obtained by plotting the
cumulative mass of particles discharged against the aperture size.
The development and improvement of MARK III was driven by the fact that there are
still flaws which lead to inaccurate PSD as particles are discharged before or after
their equivalent aperture size. Some of those flaws are;
 Loss of particles after they are discharged by the spring.
 Error is measurement of spring length (height) as discussed in section 4.4.1.
 Extension of spring from one end only leading to non-uniform aperture sizes.
The proposed improvements for the above flaws are discussed in the forthcoming
section of future work and improvements.
The chapter 2 of this thesis, addresses the main fundamentals of the particles which
includes the definitions of particle shape, size, diameter and density. The particle
shape in particular is very important as it addressed the concept of sphericity which

65
is very important for sizing particles, as most real life particles are not sphere. There
was also a brief review of particle size distribution (PSD). Moreover, types of PSD,
their representation and methods of displaying PSD were discussed.
Also in chapter 2, various techniques presently available for particle sizing were
discussed along with their advantages and limitations. It was found that most of
these conventional methods were expensive, not robust enough to be used in
aggressive environments thus incapable of on-line particle size measurement,
inability to handle large masses of samples and had complicated operating
procedures. Lastly, all the helical spring based particle size analysers preceding
MARK III were discussed.
Chapter 3 looked into apparatus, experimental set-up and methodology of the
experiments conducted to evaluate the performance of the MARK III. The
performance of MARKIII was evaluated by methods of comparison with sieve data,
variations of pulse rate and fluidisation. Additionally, the newly installed digital
calibre to measure the extended length of the spring, was discussed.
In chapter 4, the experimental results and discussion were presented. This is
considered to be the nucleus and mainstay of the whole thesis. This chapter consists
of four sub-sections.
Firstly, a comparison between data obtained by sieves and MARK III was made. The
PSD data curve showed that sieve and MARK III both have defects. This is due the
fact that sieve discharges a particle on its larger dimension (because of square
apertures) whereas MARK III discharges the particle on its smallest dimension
(because of slotted aperture). Additionally, it was noted that in MARK III up to 81%
of the discharged particles are retrieved compare to 78% in sieves.
This concludes that the performance of MARK III is not extraordinarily better than
sieves and improvements are needed.

66
In second section of chapter 4, the change in pulse rate for different particle size
ranges was analyzed. This was done to evaluate the performance of MARK III as well
as finding the best pulse rate to operate at. The experiments were carried out using
glass ballotini sample mass in the size range of 180-1000 μm with constant pulse rate
combined with different particle sizes and constant particle size combined with
different pulse rates. The result showed that as the particle sizes increased, the
particles took more time to be discharged but higher percentage of them was
discharged. Also, as the pulse rate was increased the particles were discharged
quicker. Variation in pulse rate was inconclusive on amount of particles discharged.
Hence it can be concluded that MARK III gives better performance with higher pulse
rate.
The third section of the chapter 4 overlooks the experiments done in light of
principle of fluidisation. The experiments were conducted using glass ballotini
sample masses of 5, 10, 20, 50 and 100g for the particles size range of 212-850 μm.
The pressure drop was plotted against the air flow rate. The results showed that
pressure drop increases as the mass increases and as the particle size decreases. For
instance, of all the combinations discussed in section 4.3, the 100g of 212-300 μm
has highest pressure drop. This is because the higher masses and smaller sized
particles are relatively more difficult to be fluidized. Hence there was no minimum
fluidization for the 100g of 212-300 and 300- 425 μm.
The most interesting result was obtained from the experiments conducted on 100g
of 425-500. The results showed two minimum fluidization points. The second of
those minimum fluidisation points was at very high flow rate. This showed that if the
flowrates for 100g of 212-300 and 300-425 was increased even more they would
have eventually reached minimum fluidisation point.

67
Also it was noticed that manometer has no direct contact with the outlet air flow
rate which shows that pressure drop reading from manometer has a certain degree
of error. This affects the fluidisation data.
Therefore, a conclusion can be made that pressure drop is less for larger particles
which makes MARK III more suitable for relatively larger particles.
In the last section of chapter, analysis was done on newly installed digital calibre to
measure the length of the extension of spring. The analysis showed that digital
calibre almost halves the error conducted by previous method of measuring the
spring length.
5.2. FUTURE WORK AND IMPROVEMENTS
The proposed improvement for loss of particles is to either improve the inside of the
device where particles get stuck or to device a way of calculating in-situ mass
measurement. For instance, some particles get stuck to the tape which is used help
the spring stay joint with conical base holder. A non-sticky rubber device or glue
could be used instead of the tape. Some particles cling on to the inside of glass
boundary of the instrument. A non-gluey medium similar to that of material used as
mesh screen could be used on the inside of the cylindrical glass enclosure to prevent
that.
The error in measuring length of the spring was halved by installing digital calibre. It
is thought that the maximum error of 35% is due the fact that for every 200 steps,
the spring does not extend uniformly. Extending the spring from both ends is the
obvious proposed remedy to overcome this non-uniform extension of spring.
However, the consideration of converting back to using horizontal spring design
should not be ignored because of effect of gravity on uniform extension of the spring
in the vertical position. This is elaborated more in the upcoming section future ideas
for helical spring technology.

68
Furthermore, design special extension spring to be used in MARK III and also special
springs should be made with an initial tension in considerations with the particles
that are to be used in that spring.
5.2.1. NEW IDEAS AND CONSIDERATIONS
Figure 5.1: Proposed future design for Spring Particle Size Analyzer
One of the main reasons for changing from horizontal spring in MARK II to vertical
spring MARK III, was the shaking of the spring. However as suggested in above figure
that if a design similar to that of MARK II is used but instead of shaking the spring, air
flow rate could be used to agitate the particles. To avoid particles rushing off with
the air flow, a material similar to that of mesh screen can be used to block both sides.
Two mechanical arms can be used to stretch the spring from both sides like in MARK
II and unlike in MARK III.
Arguably the biggest problem in the design proposed above is measuring the mass of
the particles discharged. This nevertheless is no worse than the case in MARK III. In

69
fact in this proposed design, the discharged particles do not have to travel as far as in
MARK III. Another issue is to insert the particles in the spring for sizing. This could be
done by keeping a small open/close hole in the middle of the mesh screen. So the
hole is opened before the air is pulsed in, particles are inserted and the hole is closed.
Air pulse can still travel through the mesh screen around the closed hole while
particles are trapped in the spring to be discharged through the spring coils only
depending on their size.
The second idea is based on the mixture of sieve and spring technology. The idea for
the design proposed below was taken from the fact that air is a good medium to
agitate the particles. The whole concept given below revolves around better
agitation factor and hence better PSD.
Figure 5.2: Proposed future design for Sieve Particle Size Analyzer using air
flowrate
The design illustrates, that once particles are put inside the top sieve, it is sealed
with mesh material so that particles do not leave from the top due to air flow rate.
The air pipe enters the systemthrough the bottom container where it is sealed. The

70
air pulse travels upwards through the stack of sieves and agitates the particles in the
process.
Using air flow rate instead of shaking the stack helps the particles agitate more,
frees the particles that are stuck in the square slotted aperture of the sieves and it is
not as noisy as shaking device. All the above reasons will help obtain better PSD data.

71
REFERENCES
1. Kaye, B. H., "An investigation into the relative efficiency of different sampling
procedures", Powder Met., 9, 1962, pp. 213–234
2. Allen, T. and Khan, A. A., "Critical evaluation of powder sampling procedures",
The Chemical Engineer, 238, May 1970, pp. 108–112
3. Lettieri, P., “Fluid-Particle Systems” Lecture Notes, University College London,
2009.
4. Charlier, R. and Goosens, W., "Sampling a heterogeneous powder using a
spinning riffler", Powder Technol., 4, 1970, pp. 351–359
5. Harris, J. E. C. and Scullion, H. J., "Techniques for particle characterisation",
Proc. Soc. Anal. Chem., 10 (5), May 1973, pp. 108–114
6. Hatton, T. A., "Representative sampling of particles with a Spinning Riffler. A
stochastic model", Powder Technol., 19, 1978, pp. 227–233
7. Hawkins, A. E., "Demonstrating the sampling of heterogeneous, free–flowing,
segregating powders", Part. Part. Syst. Character., 5, 1988, pp. 23–28
8. Hawkins, A. E., The shape of powder particle outlines, Research Studies Press,
1993, ISBN 0–86380–142–0 Chapter 2, "Sampling and particle presentation".
9. Ditmars, D., DeVine, P. and Templer, M. J., "The importance of representative
sampling in the analysis of powdered and granular materials", Powder
Handling and Processing, 5 (4), November 1993.

72
10. Allen, T., Particle Size Measurement, Kluwer Academic Publishers,5th ed.,
Chapman and Hall, London , 1997.
11. Allen, T., Particle Size Measurement, 4th edition., Chapman and Hall, London ,
1990.
12. Arai., Chemistry of powder production, Chapman and Hall, London, 1996.
13. Methods for determination of particle size distribution; Pt.6,
Recommendations for centrifugal liquid sedimentation methods for powders
14. Testing aggregates / British Standards Institution; Pt.103, Methods for
determination of particle size distribution
15. J.W. Novak Jr. and J.R. Thompson, Extending the use of particle sizing
instrumentation to calculate particle shape factors
16. Hawkes, P., The beginnings of Electron Microscopy. Academic Press, 1985.
17. Rhodes, M., Introduction to Particle Technology, John Wiley and Sons Ltd,
Chichester, 2008
18. Clift, R., Seville, J., and Tuzun,U., Processing of particulate Solids,1st Ed.,
Chapman and Hall, London ,1997
19. Kerdvibulvech, K., Spring Particle Sizer, PhD Thesis, Department of Chemical
Engineering, University College London, 2008.
20. Shaeri A., Vibro-Spring Particle Size Analyser, PhD Thesis, Department of
Chemical Engineering, University College London, 1996.

73
21. Mahgerefteh H., Shaeri A., Modelling of Novel Vibro-Spring Particle Size
Distribution Analyser, AlChE, Vol47, No 3, 2001.
22. Patel K S., Vibro-Spring Particle Size Analyser, PhD Thesis, Department of
Chemical Engineering, University College London, 2001.
23. Yang, W., Handbook of fluidization and fluid-particle systems, Marcel Dekker,
New York, 2003.
24. Mahgerefteh H., Al-khoory H., A Novel vibrating Reed Technique for Particle
Size Measurements, Powder Technology, 1991.

74
APPENDICES
APPENDIX A1
Figure A1.1: Reproducibility of 5g sample of glass ballotini of the range of 180-250
μm obtained at P.D = 60 and P.R =0.5
Figure A1.2: Reproducibility of 5g sample of glass ballotini of the range of 250-
355μm obtained at P.D = 30 and P.R =1
0
1
2
3
4
5
6
0 2 4 6 8 10
Cumulativemass(g)
Number of time steps (minutes)
1st run (180-250)
2nd run (180-250)
Average
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 2 4 6 8
Cumulativemass(g)
1st run (250-355)
2nd run (250-355)
Average

75
Figure A1.3: Reproducibility of 5g sample of glass ballotini of the range of 250-
355μm obtained at P.D = 0.5 and P.R =60
APPENDIX A2
Figure A2.1: Reproducibility of 100g sample of glass ballotini of range of 212-
300μm
0
1
2
3
4
5
6
0 2 4 6 8
Cumulativemass(g)
1st run (850-1000)
2nd run (850-1000)
Average
0
20
40
60
80
100
120
0 50 100 150 200
Pressurechange,KPa
Average

76
Figure A2.2: Reproducibility of 100g sample of glass ballotini of range of 300-425
μm
500μm
0
20
40
60
80
100
120
0 50 100 150
Pressurechange,KPa
average
0
10
20
30
40
50
60
70
0 50 100 150 200
Pressurechange,KPa
100g, 3rd set of readings
Average

77
600μm
850μm
0
10
20
30
40
50
60
70
0 50 100 150 200
Pressurechange,KPa
Average
0
10
20
30
40
50
60
70
0 50 100 150 200
Pressurechange,KPa
Average

78
APPENDIX A3
Figure A3.1: Graphical representation of comparison between digital and old
method as extended length of the spring against number of steps
Figure A3.2: Graphical representation of comparison between digital and old
method as cumulative mass against extended length of the spring
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 1000 2000 3000 4000 5000 6000
lengthofspring(cm)
number of steps
digital calibre
Old Analogue calibre
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 0.5 1 1.5 2 2.5 3 3.5
cumulativemass(g)
length of spring (cm)
digital calibre
Old Analogue calibre

79

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