Pharmaceutical Engineering

1. Fluid flow, Heat transfer & Mass transfer
Md. Shahin Sarker
Lecturer, Dept. of Pharmacy
Jashore University of Science & Technology (JUST)
Course Tittle: Pharmaceutical Engineering- I
Course N0.:PHAR 3113

2. What is Fluid?
• A fluid is a state of matter (or matter- in- transition state) in which its molecules move
freely and do not bear a constant relationship in space to other molecules
• Thus it has the ability to take up the shape of its container
• Fluids are;
1. Liquid: e.g. blood, I.V.infusions
2. Gas: e.g. O2,N2O
3. Vapor (transition from liquid to gas): e.g. N2O (under compression in cylinder),
volatile inhalational agents (halothane,isoflurane,etc.)
4. Sublimate (transition from solid to gas bypassing liquid state): Dry ice (solid CO2),
iodine

3. Fluid flow
• A fluid is a substance that continually deforms (flows) under an applied shear stress.
Fluids are a subset of the phases of matter and include liquids, gases. Fluid flow may
be defined as the flow of substances that do not permanently resist distortion
• Fluid flow is also defined as the quantity of fluid (gas, liquid, vapor or sublimate)
that passes a point per unit time. A simple equation to represent this is:
Flow(F)=
𝑸 𝒖 𝒂 𝒏 𝒕 𝒊 𝒕 𝒚 ( 𝑸)
𝑻 𝒊 𝒎 𝒆 ( 𝒕)
• The subject of fluid flow can be divided into
1. Fluid statics
2. Fluid dynamics
• The flow of fluid through a pipe can be divided into;
1. Laminar flow
2. Turbulent flow

4. Fluid flow
1. Fluid statics: Fluid static's deals with the fluids at rest in equilibrium
 Behavior of liquid at rest
 Nature of pressure it exerts and the variation of pressure at different layers
2. Fluid Dynamics: Fluid dynamics deals with the study of fluids in motion. This
knowledge is important for liquids, gels, ointments which will change their flow
behavior when exposed to different stress conditions.
• Identification of type of flow is important in
1. Manufacturing of dosage forms
2. Handling of drugs for administration

5. Laminar flow
• Laminar flow is one in which the fluid particles move in layers or laminar with one
layer sliding with other.
 There is no exchange of fluid particles from one layer to other
 It is smooth, steady and orderly flow of fluid in a tube
 All the fluid molecules move in a straight line. Therefore they move in parallel
layers or laminae with no disruption between the layers
 Velocity of flow is greatest in the axial stream (center of the tube). It becomes
progressively slower as the layers move to the periphery
 Axial stream velocity is twice the mean flow velocity
 Velocity of the layer in contact with the wall is virtually zero

6. Turbulent Flow
• When velocity of the water is increased the thread of the colored water disappears and
mass of the water gets uniformly colored. There is complete mixing of the solution and
the flow of the fluid is called as turbulent flow.
 Fluid does not move in orderly manner
 The fluid molecules become more disorganized
 They form swirls and eddies as they move down the pressure gradient in haphazard
manner
 There is increased resistance to flow as the eddy currents interfere with each other
 Therefore greater energy is required for a given flow rate, compared to when the
flow is laminar
The velocity at which the fluid changes from laminar flow to turbulent flow that
velocity is called as critical velocity

7. Flow of Fluid

8. Factors Affecting Flow
1. Pressure: flow is directly proportional to the pressure difference across the tube
2. Radius: flow is directly proportional to the fourth power of the radius (or diameter) of
the tube
3. Length: flow is inversely proportional to the length of the tube
4. Viscosity: flow is inversely proportional to the viscosity of the fluid
• Viscosity (η) is the property of a fluid that causes it to resist flow. It is a measure of the
frictional forces acting between the layers of fluid as it flows along the tube.
 Viscosity of a liquid decreases with increased temperature, while viscosity of a gas
increases with increased temperature
 From Hagen-Poiseuille equation, the more viscous a fluid is the lesser the flow. This
however applies to laminar flow and not turbulent flow, where flow is dependent on the
density of the fluid.

9. What is Heat ?
• Heat: "The energy in transit is termed heat“. While Aristotle was of the opinion that
fire was one of the four primary elements, Plato thought that the heat was sort of motion
of particles; accordingly there are two theories of heat. Any theory should be able to
explain the facts given below :
i. Whenever there is an exchange of heat, heat is consumed (heat lost by the hot body
is always equal to heat gained by the cold body).
ii. The heat flow takes place from higher to lower temperature.
iii. The substances expand on heating.
iv. In order to change the state of a body from solid to liquid or liquid to gas without
rise in temperature, certain amount of heat is required.
v. When a body is heated or cooled its weight does not change.
• According to the modern or dynamical theory of heat: "Heat is a form of energy. The
molecules of a substance are in parallel motion. The mean kinetic energy per molecule of
the substance is proportional to its absolute temperature".

10. Heat Transfer
• Heat transfer may be defined as "The transmission of energy from one region to
another as a result of temperature gradient".
• In heat transfer the driving potential is temperature difference whereas in mass transfer
the driving potential is concentration difference. In mass transfer we concentrate upon
mass motion which result in changes in composition, and are caused by the variations in
concentrations of the various constituent species. This transfer, in literature, is also known
as "diffusion".
• The study of heat transfer is carried out for the follows purposes :
1. To estimate the rate of flow of energy as heat through the boundary of a system under
study (both under steady and transient conditions).
2. To determine the temperature field under steady and transient conditions.

11. Heat Transfer
• In almost every branch of engineering, heat transfer (and mass transfer) problems are
encountered which cannot be solved by thermodynamic reasoning alone but require an
analysis based on heat transfer principles. The areas covered under the discipline of heat
transfer are :
1. Design of thermal and nuclear power plants including heat engines, steam generators,
condensers and other heat exchange equipment's, catalytic converters, heat shields for
space vehicles, furnaces, electronic equipment's etc.
2. Internal combustion engines.
3. Refrigeration and air conditioning units.
4. Design of cooling systems for electric motors, generators and transformers.
5. Heating and cooling of fluids etc. in chemical operations.
6. Construction of dams and structures; minimization of building-heat losses using
improved insulation techniques.
7. Thermal control of space vehicles.
8. Heat treatment of metals.
9. Dispersion of atmospheric pollutants.

12. Mode of heat transfer
• Heat transfer takes place by the following three modes :
1. Conduction
2. Convection
3. Radiation
• Heat transmission, in majority of real situations, occurs as a result of combinations of
these modes of heat transfer. Example : The water in a boiler shell receives its heat from
the fire bed by conducted, convected and radiated heat from the fire to the shell,
conducted heat through the shell and conducted and convected heat from the inner shell
wall, to the water. Heat always flows in the direction of lower temperature.
• The above three modes are similar in that a temperature differential must exist and the
heat exchange is in the direction of decreasing temperature; each method, however, has
different controlling laws.

13. Conduction
• "Conduction" is the transfer of heat from one part of a substance to another part of the
same substance, or from one substance to another in physical contact with it, without
appreciable displacement of molecules forming the substance.
• In solids, the heat is conducted by the following two mechanisms :
i. By lattice vibration (the faster moving molecules or atoms in the hottest part of a
body transfer heat by impacts some of their energy to adjacent molecules).
ii. By transport of free electrons (Free electrons provide an energy flux in the direction
of decreasing temperature. For metals, especially good electrical conductors, the
electronic mechanism is responsible for the major portion of the heat flux except at
low temperature).
• In case of gases, the mechanism of heat conduction is simple. The kinetic energy of a
molecule is a function of temperature. These molecules are in a continuous random
motion exchanging energy and momentum. When a molecule from the high temperature
region collides with a molecule from the low temperature region, it loses energy by
collisions.
• In liquids, the mechanism of heat is nearer to that of gases. However, the molecules are
more closely spaced and intermolecular forces come into play.

14. Convection
• "Convection" is the transfer of heat within a fluid by mixing of one portion of the fluid with another.
 Convection is possible only in a fluid medium and is directly linked with the transport of
medium itself.
 Convection constitutes the macro-form of the heat transfer since macroscopic particles of a
fluid moving in space cause the heat exchange.
 The effectiveness of heat transfer by convection depends largely upon the mixing motion of the
fluid.
• This mode of heat transfer is met with in situations where energy is transferred as heat to a flowing
fluid at any surface over which flow occurs. This mode is basically conduction in a very thin fluid
layer at the surface and then mixing caused by the flow. The heat flow depends on the properties of
fluid and is independent of the properties of the material of the surface. However, the shape of the
surface will influence the flow and hence the heat transfer.
1. Free or natural convection: Free or natural convection occurs when the fluid circulates by virtue
of the natural differences in densities of hot and cold fluids; the denser portions of the fluid move
downward because of the greater force of gravity, as compared with the force on the less dense.
2. Forced convection: When the work is done to blow or pump the fluid, it is said to be forced
convection.

15. Radiation
• "Radiation" is the transfer of heat through space or matter by means other than conduction or
convection.
• Radiation heat is thought of as electromagnetic waves or quanta (as convenient) an emanation of
the same nature as light and radio waves. All bodies radiate hear, so a transfer of heat by radiation
occurs because hot body emits more heat than it receives and a cold body receives more heat than
it emits. Radiant energy (being electromagnetic radiation) requires no medium for propagation and
will pass through vacuum.
• The properties of radiant heat in general, are similar to those of light. Some of the properties are :
1. It does not require the presence of a material medium for its transmission.
2. Radiant heat can be reflected from the surfaces and obeys the ordinary laws of reflection.
3. It travels with velocity of light.
4. Like light, it shows interference, diffraction and polarization etc.
5. It follows the law of inverse square.
• The wavelength of heat radiations is longer than that of light waves, hence they are invisible to the
eye.

16. Mass Transfer
• In a system consisting of one or more components whose concentrations vary from point
to point, there is a natural tendency for the transport of different species from the region
of high to those of low concentration. This process of transfer of mass as a result of the
species concentration difference in a system/mixture is called mass transfer.
• So long as there is concentration difference mass transfer will occur. Some examples of
mass transfer are:
1. Refrigeration by the evaporation of liquid ammonia in the atmosphere of H2 in
Electrolux refrigerator.
2. Humidification of air in cooling tower.
3. Evaporation of petrol in the carburetor of an I.C. engine.
4. Neutron diffusion within nuclear reactors.
5. Dissolution of sugar added to a cup of coffee.
6. The separation of the components of a mixture by distillation or absorption.
7. The transfer of water vapor into dry air, drying and evaporation.

17. Modes of Mass Transfer
• The mechanism of mass transfer depends greatly on the dynamics of the system in which
it occurs. Like those of heat transfer, there are different modes of mass transfer. which
are:
1. Mass transfer by diffusion
2. Mass transfer by convection
3. Mass transfer by change of phase
1) Mass transfer by diffusion (molecular or eddy diffusion): The transport of water on
a microscopic level as a result of diffusion from a region of high concentration to a
region of low concentration in a system/mixture of liquids or gases is called molecular
diffusion. It occurs when a substance diffuses through a layer of stagnant fluid and may
be due to concentration, temperature or pressure gradients. In a gaseous mixture,
molecular diffusion occurs due to random motion of the molecules.
• When one of the diffusing fluids is in turbulent motion, the eddy diffusion takes place.
Mass transfer is more rapid by eddy diffusion than by molecular diffusion. An example
of an eddying diffusion process is dissipation of smoke from a smoke stack. Turbulence
causes mixing and transfer of smoke to the ambient air.

18. Modes of Mass Transfer
2. Mass transfer by convection: Mass transfer by convection involves transfer between a
moving fluid and a surface or between two relatively immiscible moving fluids. The
convective mass transfer depends on the transport properties and on the dynamic
(laminar or turbulent) characteristics of the flowing fluid. Example: The evaporation of
ether.
3. Mass transfer by change of phase: Mass transfer occurs whenever a change from one
phase to another takes place. The mass transfer in such a case occurs due to simultaneous
action of convection and diffusion. Some examples are:
a) Hot gases escaping from the chimney rise by convection and then diffuse into the air
above the chimney.
b) Mixing of water vapor with air during evaporation of water from the lake surface (partly
by convection and partly by diffusion).
c) Boiling of water in open air: there is first transfer of mass from liquid to vapor state and
then vapor mass from the liquid interface is transferred to the open air by convection as
well as by diffusion.