1




Innovative Heat Exchanger Design
    for Wind Turbine Applications
                   In corporation with Vestas
2




• Project Supervisor   Professor Winoto SH

• Group members        Tan Tze Peng Wilson
                       Claren...
3



    Scope of Presentation
           • Introduction

• Heat Exchanger Model for Experiment

       • Proposed Experim...
4



1. Introduction
• Previous Semester

• Verification of Calculations

• Designing the Heat Exchanger for Experiment

•...
5


Background
• We hope to be able to manufacture a heat exchanger which we have
  previously designed and test it out vi...
6


2. Heat Exchangers Model for
         Experiment

  • Evaluation of Plate-Fin Surfaces

   • Selection of Fin Configur...
Evaluation of Plate-Fin Surfaces
5 Categories of Plate-Fins

•   Plain
•   Wavy
•   Offset strip
•   Louver
•   Pin Fin
Plain Fins

• Straight fins that are uninterrupted (uncut)

• Any complex shape can be formed as desired, depending on how...
Wavy Fins

• Uncut surfaces in the flow direction, and have cross-sectional shapes
  similar to those of plain surfaces. H...
Offset Strip Fins

• The fin has a rectangular cross section, and is cut into small strips of
  length. Every alternate st...
Louver Fins

• Louvers can be made in many different forms and shapes.

• The j factors are higher for louver fins than fo...
Pin Fins

• Can be manufactures at very high speed continuously from a wire of
  proper diameter.

• Surfaces compactness ...
Selecting of Fin Configuration
 Optimize Heat Exchanger Design based on the following factors:

 •   Pressure Drop
 •   He...
Pressure Drop

If pressure drop and heat transfer are the most critical factors, then the
heat transfer per unit of pressu...
Size

If size is the overall driving design factor then a good figure of merit is
heat transfer per unit height.


       ...
Weight

If weight is the overall driving design factor, then a good figure of merit
is heat transfer per unit weight.
Cost

In general, pin fins, which are incorporated directly into the casting of
the heat exchanger, are the least expensiv...
Comparison of All Parameters

    Ranking 1 being the most desirable and ranking 5 being the least desirable

      Fins
 ...
Scaling Laws for Heat Exchangers




                          doreen
The following ratios apply to the geometric
parameters:
Hydrauli Length          Surface     Flow       Volume
c          ...
Assumptions
• The number of tubes in the heat exchanger is the
  same.

• The physical properties are fixed, based on the
...
4 scenarios
1. Same mass flow rate,      (for each stream)

1. Same Reynolds Number, Re

1. Same flow velocity, G

1. Same...
Resultant Parameters
We aim to find the following:

• Q2, heat load removed by the prototype(scaled
  down model).

• The ...
Summary
Sample Calculations
• Flow regime of the original 3x3x0.15 m3 heat
  exchanger is laminar

• Hence, when applying the scal...
Sample Calculations
For mass flow rate
                     Re1 = Re2




                                 Subscripts:
   ...
Sample Calculations
• For the overall heat transfer coefficients, U
Sample Calculations
• NTU – Number of Transfer Units ratio




Note: NTU2 = NTU1 means e2 = e1,
What if NTU2 ≠ NTU1?

 •e2 ≠ e1

 •Obtain NTU2 from
 the relevant ratio
 • Using the NTU2
 value together with
 Cmin/Cmax ...
Sample Calculations
• Heat load, Q2

• Note: only inlet temperatures are involved
Sample Calculations
• Ratio of pressure drops

                Where f = Fanning friction factor




• With ∆P2 known, we ...
For the Experiment
Parameters that we can control:

• Inlet temperatures, Twater,in Tair,in ≈Tamb

• Wind tunnel air speed...
Discussions
• Unable to scale down DH

• Actual DH = 3.23 mm (wavy, air side) and DH = 2.87
  mm (plain, water side)

• Di...
Suggestions
• Build a scaled down HX

• Maintaining the original DH

• Since the entire HX consists of stacks of plates
  ...
35



3. Proposed Experiment

          • Purpose

         • Objectives

         • Theory

     • Experiment Setup

    ...
Purpose
The purpose of this experiment is to collect
experimental data from a scaled down prototype of
the wind turbine an...
Objectives
1. Manufacture a smaller prototype of heat exchanger
   based on the scaling down theory calculation

2. Modify...
Theory
Determination of surface characteristics:

  In the experiment:
• the flow rates on both fluid sides of the exchang...
Heat capacity ratio    For an unmixed –
unmixed crossflow exchanger, the relationship
will be:
For Cr 0,

 the heat capacity rate is determined from the
 measured mass flow rate on each fluid side and
 the specific he...
The overall heat transfer coefficient Ua based on the total
  airside surface area Aa is then evaluated from NTU as


  Th...
Then


 The test cores are generally new, and no fouling
 or scale resistance is on either side, so the
 corresponding res...
The term      in equation 1.3 is the extended
surface efficiency of the air side surface and is
related to the fin efficie...
For many plate fin surfaces, the relation for the
 straight fin with constant conduction cross
 section may be used to a g...
The Stanton number St and the Colburn factor j
are then evaluated from their definitions:




The Reynolds number on the u...
Determination of the factor is made under steady fluid
 flow rates. For a given fluid flow rate on the unknown f
 side, th...
Here Kc and Ke are sudden contraction and expansion
pressure loss coefficients presented in Appendix 1. Tests
are repeated...
Liquid Flow System

• Stainless steel piping

• Gear pump

• Resistive Heater (Watlow®)

• Mass flow rate meter (D25 Micro...
Air Sampling System
 Consist of

• Thermocouple (type T) x 2
  A type T thermocouple with a
  measurement range of -200
  ...
Pressure Drop Measurement

Consist of

• Pressure differential Transducer (Validyne DP-103) x 2
 To measure the pressure d...
Schematic diagram of Test Setup
                                                       2MX1M




                         ...
Data Acquisition




     Data Acquisition (DAQ)
  Acquisition of signals &waveforms &processing the signals to obtain des...
Start Up Procedure

Power up the DAQ unit

Switch on the gear pump to start water circulation

Switching on the heater aft...
Lab Equipment

                          DAQ with Labview
                          Software




     The NUS industrial
 ...
Lab Equipment

                         Interior of a wind tunnel




      The Wind turbine
         and motor
57



4. Fouling of Heat Exchangers
             • Literature Survey

        • General Methods of Fouling

         • Hea...
58



Literature Survey
• Fouling is defined as the accumulation of deposits on the
  surface of the heat exchangers

• De...
59


Deposition of Foulant




• Region A represents the initiation of adhesion
• Region B represents the steady growth of...
60


  Why is Fouling bad?




Fin Cooler tubes severely corroded   Deposits build-up on the inside of a heat   Wall thinn...
61




General Methods of Fouling
• Adhesion
• Particulate deposition
• Corrosion
62




Adhesion
• physical interaction between the foulant and the
  heat exchanger surface.

• 3 types of interaction:
  ...
63




Particulate Deposition
• Particle arriving at a surface can be by two
  mechanism:
  ▫ gravitational and: stationar...
64



Corrosion
• Corrosion means the breaking down of essential
  properties in a material due to chemical reactions with...
65



Heat Exchanger Cleaning
• Circulation of Sponge Rubber Balls

• Brush and Cage System

• Air and Gas Injection

• Ma...
66


Circulation of Sponge Rubber Balls
• Sponge rubber balls which are slightly larger (by 2mm)
  then the diameter of th...
67
68



Brush and Cage System
• The operating method of this system is very similar to that of the
  Sponge rubber Ball.

• ...
69



Air and Gas Injection
• Air and gas injection is usually used in areas where
  accessibility is difficult e.g. shell...
70



Magnetic Device
• The main application of magnetic devices is to eliminate
  scale formation in pipes.

• It is coul...
71


Soot Blower
• The fundamental of the soot blower is to remove soot that is
  built up in steam boiler.

• Steam is ch...
72
73


Water Washing
• Water washing of heat exchanger is the process of
  introducing jets of water into the system. This h...
74



Galvanic Protection
• Galvanic protection involves the study of electric
  current that is involved in the corrosion...
1. fouling deposit provides additional thermal
   resistance to heat transfer besides those originally
   present due to t...
• increased capital investment

• additional operating costs

• loss of production

• cost of remedial action
thermal resistance Rf across a solid barrier is given by



l is the solid thickness and kf is its thermal conductivity


...
• boundary layers, situated
between the deposits and the
fluids, provide small amount of
thermal resistance to heat flow
d...
we can write Rf in terms of the overall heat transfer coefficient for
                            fouling Uf




general f...
• Besides increasing the thermal resistance, foulant layer have two
additional negative effects

• Firstly, once deposit r...
(three fundamental stages that describe process of deposition)

1. The diffusional transport of the foulant across the
  b...
By combining these three components, rate of deposition
growth can be defined as the difference between the rates
        ...
• A = straight line
relationship, deposit thickness
increases at a constant rate with
time after the initial adhesion
peri...
Change in Heat Transfer
                             Coefficient




                            Change due to
   Change d...
85



Detailed Analysis of Anti-Fouling
Methods : Air Side : Sonic Technology
• Similar to vibration caused by sound energ...
Sonic Technology (cont’)
• commercially available sonic horn model #CS-125
  designed by IAC (Industrial Accessories Compa...
Corona Discharge

• ionizes the fluid so as to create a plasma around
  the electrode
• may be positive or negative
• Neut...
88




Water Side : Electronic Anti-
 Fouling Technology
• Most prominent is formation of scales
• Hard water is heated
• ...
Electronic Anti-fouling technology




 Overview of Electronic Anti-fouling technology
Electronic Anti-fouling technology
• Induced electric field to increase the ions and crystals
  collision frequency
• Prod...
Electronic Anti-fouling technology
• Resulting in collision, precipitation as well as
  coagulation.
• Converted into inso...
Electronic Anti-fouling technology




      Pressure drop across HE for 4 different cases
Electronic Anti-fouling technology




  Overall Heat Coefficient   Fouling factors
94



Conclusion and Recommendations

                ▫ Conclusions
        Heat Exchanger Model for Experiment
         ...
95
Conclusions : Heat Exchanger Model
for Experiment
• Manufacturability constrains.

• If we are to scale down the hydrau...
96


Conclusions : Proposed Experiment
• By using the experimental results, we are able to
  determine Stanton number St, ...
97

Conclusions : Fouling of Heat
Exchanger
• With innovative methods employed on the air side and
  water side of the hea...
98

Conclusions : Recommendations for
Future Work
• With the stage set for the experiment to be conducted, our future
  ju...
ME3102 Final Presentation
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ME3102 Final Presentation

  1. 1. 1 Innovative Heat Exchanger Design for Wind Turbine Applications In corporation with Vestas
  2. 2. 2 • Project Supervisor Professor Winoto SH • Group members Tan Tze Peng Wilson Clarence Chen Jun Jie Chen Xianghao Tan Bao Lun Teh Ter Chen Yeo Shu Feng Doreen Ye Xiu Yin
  3. 3. 3 Scope of Presentation • Introduction • Heat Exchanger Model for Experiment • Proposed Experiment • Fouling of Heat Exchanger • Conclusion and Recommendations
  4. 4. 4 1. Introduction • Previous Semester • Verification of Calculations • Designing the Heat Exchanger for Experiment • Procedures and Guidelines being drafted for the experiment in wind tunnel. • Comparison between Experimental and Theoretical results. • Fouling as a Menace in the Heat Industry. • Innovative and cost-effective methods.
  5. 5. 5 Background • We hope to be able to manufacture a heat exchanger which we have previously designed and test it out via experiments. • Our initial plan was to source for any local heat exchanger companies to help fabricate the design. However we faced two major constrains. ▫ The first constrain was that no local company fabricates plate-fin heat exchangers. ▫ Secondly, the budget not enough to custom build a heat exchanger and purchasing equipments for the wind tunnel testing. • We have decided to do the theoretical calculation for the scaling down as well as to brainstorm for innovative anti-fouling ideas. • Facilitating our juniors who will undertake the project and carry out the verification and testing of the heat exchanger
  6. 6. 6 2. Heat Exchangers Model for Experiment • Evaluation of Plate-Fin Surfaces • Selection of Fin Configuration • Scaling Law of Heat Exchangers • Sample Calculation
  7. 7. Evaluation of Plate-Fin Surfaces 5 Categories of Plate-Fins • Plain • Wavy • Offset strip • Louver • Pin Fin
  8. 8. Plain Fins • Straight fins that are uninterrupted (uncut) • Any complex shape can be formed as desired, depending on how the fin material is folded. • Rectangular and Triangular passages are most common • Used in applications where the allowable pressure drop is low • Preferred for very low Reynolds numbers applications. ▫ -with interrupted fins, at low Re, the advantage of the high heat transfer coefficient value of the interrupted fins is diminished while the cost remains high.
  9. 9. Wavy Fins • Uncut surfaces in the flow direction, and have cross-sectional shapes similar to those of plain surfaces. However, they are wavy in the flow direction. • The waveform provides effective interruptions to the flow and induces very complex flows - higher heat transfer coefficient for wavy fin to that of an equivalent plain fin. • However, the heat transfer coefficient for wavy fins is lower than that for interrupted fins such as offset or louver fins. • Since there are no cuts in the surface, wavy fins is preferred when potential fouling or clogging problem might occurred.
  10. 10. Offset Strip Fins • The fin has a rectangular cross section, and is cut into small strips of length. Every alternate strip is displaced (offset) by about 50% of the fin pitch in the transverse direction. • Heat transfer coefficients for the offset strip fins are 1.5 to 4 times higher than those of plain fin geometries. However, the corresponding friction factors are also high. • The ratio of j/f for an offset strip fin to j/f for a plain fin is about 80%. • Offset strip fins are used in the approximate Re range 500 to 10000.
  11. 11. Louver Fins • Louvers can be made in many different forms and shapes. • The j factors are higher for louver fins than for the offset strip fin at the same Reynolds number, but the f factors are even higher than those for the offset strip fin geometry. • Since the louver fin is triangular, it is generally not as strong as an offset strip fin which has a relatively large flat area for brazing.
  12. 12. Pin Fins • Can be manufactures at very high speed continuously from a wire of proper diameter. • Surfaces compactness achieved by pin fin geometry is much lower than that of offset strip or louver fin surfaces. • The overall exchanger performance is also lower than other types of surfaces. • Potential application for pin fins is at very lower Reynolds number (Re<500). • Due to vortex shedding behind the round pins, noise and flow induced vibration may be a problem.
  13. 13. Selecting of Fin Configuration Optimize Heat Exchanger Design based on the following factors: • Pressure Drop • Heat Transfer • Size • Weight • Cost To help us in our selection of the best fin configuration, we plotted graphs for comparing different fin configurations under the listed factors. From there we will be able to study the different fin types and formulate a table as a basis for comparison.
  14. 14. Pressure Drop If pressure drop and heat transfer are the most critical factors, then the heat transfer per unit of pressure drop (i.e. j-Colburn factor divided by f-friction factor) will show a good comparison between different types of extended surface. Heat Transfer over Pressure Drop Figure of Merit 0.6 0.5 j/f (j-colburn / f- friction) 0.4 plain fin 0.3 strip fin louvered fin 0.2 wavy fin pin fin 0.1 0 0 2000 4000 6000 8000 10000 12000 Reynolds Number
  15. 15. Size If size is the overall driving design factor then a good figure of merit is heat transfer per unit height. Size Figure of Merit 0.0035 Heat Transfer per unit height 0.003 0.0025 0.002 pin fin louvered fin 0.0015 strip fin wavy fin 0.001 plain fin 0.0005 0 0 2000 4000 6000 8000 10000 12000 Reynolds Number
  16. 16. Weight If weight is the overall driving design factor, then a good figure of merit is heat transfer per unit weight.
  17. 17. Cost In general, pin fins, which are incorporated directly into the casting of the heat exchanger, are the least expensive. The other fin type cost about the same with some minor differences in set up costs. Fins Cost Configuration Increasin Pin fins 1 g cost Plain fins 2 Wavy fins 3 Offset Strip fins 4 Louvered fins 5
  18. 18. Comparison of All Parameters Ranking 1 being the most desirable and ranking 5 being the least desirable Fins ∆P Size Weight Cost Average Configuration Plain fins 1 5 4 2 3 Louvered fins 3 2 1 5 2.75 Offset Strip fins 2 3 3 4 3 Wavy fins 4 4 2 3 3.25 Pin fins 5 1 5 1 3 Our Selection  Plain fins for water-side (taking fouling into consideration)  Using excel to find the best combination for air-side fin type
  19. 19. Scaling Laws for Heat Exchangers doreen
  20. 20. The following ratios apply to the geometric parameters: Hydrauli Length Surface Flow Volume c Area, As area, Ac Diameter dh2 = dh1/N L2 = L1 /N As2 = As1/N2 Ac2 = V2 = Ac1/N2 V1/N3 where N = scaling factor
  21. 21. Assumptions • The number of tubes in the heat exchanger is the same. • The physical properties are fixed, based on the inlet conditions. • The inlet temperatures are fixed. • Each flow stream is treated the same.
  22. 22. 4 scenarios 1. Same mass flow rate, (for each stream) 1. Same Reynolds Number, Re 1. Same flow velocity, G 1. Same pressure drop, ∆P Based on the book: Compact Heat Exchangers, Selection, Design and Operation by J.E. Hesselgreaves
  23. 23. Resultant Parameters We aim to find the following: • Q2, heat load removed by the prototype(scaled down model). • The pressure drop ∆p.
  24. 24. Summary
  25. 25. Sample Calculations • Flow regime of the original 3x3x0.15 m3 heat exchanger is laminar • Hence, when applying the scaling laws, flow regime of the prototype must be consistent, ie, laminar • Keep Reynolds Number the same • Nusselt number for laminar flow, • If turbulent, NuD = 0.023ReD0.8Pr0.4 (Dittus-Boelter)
  26. 26. Sample Calculations For mass flow rate Re1 = Re2 Subscripts: 1 - original 2 - prototype
  27. 27. Sample Calculations • For the overall heat transfer coefficients, U
  28. 28. Sample Calculations • NTU – Number of Transfer Units ratio Note: NTU2 = NTU1 means e2 = e1,
  29. 29. What if NTU2 ≠ NTU1? •e2 ≠ e1 •Obtain NTU2 from the relevant ratio • Using the NTU2 value together with Cmin/Cmax ratio get a new e2 value
  30. 30. Sample Calculations • Heat load, Q2 • Note: only inlet temperatures are involved
  31. 31. Sample Calculations • Ratio of pressure drops Where f = Fanning friction factor • With ∆P2 known, we can size the pump.
  32. 32. For the Experiment Parameters that we can control: • Inlet temperatures, Twater,in Tair,in ≈Tamb • Wind tunnel air speed, u2 • Fluid properties, e.g. cp • Mass flow rate of water, determined from the pump,
  33. 33. Discussions • Unable to scale down DH • Actual DH = 3.23 mm (wavy, air side) and DH = 2.87 mm (plain, water side) • Difficult to manufacture • After scaling down, flow passage will be too narrow • Heat loss may not be through convection only • Possibly through conduction
  34. 34. Suggestions • Build a scaled down HX • Maintaining the original DH • Since the entire HX consists of stacks of plates with the fins attached, • Can conduct experiments to calculate how much heat, qp, 1 plate can remove • ∴Total heat load = N x qp
  35. 35. 35 3. Proposed Experiment • Purpose • Objectives • Theory • Experiment Setup • Startup Procedure • Tables and Program
  36. 36. Purpose The purpose of this experiment is to collect experimental data from a scaled down prototype of the wind turbine and verify the data against theoretical values derived from the excel spreadsheet calculations to prove that it is within acceptable range of heat energy dissipation by the actual heat exchanger.
  37. 37. Objectives 1. Manufacture a smaller prototype of heat exchanger based on the scaling down theory calculation 2. Modify and introduce measurement apparatus in wind tunnel to accurately collect selected design parameters and data. 3. Design and build a liquid flow system (hot side) to accurately facilitate liquid-side flow and heat transfer measurements. 4. Compare the experimental results against the theoretical excel spreadsheet calculations.
  38. 38. Theory Determination of surface characteristics: In the experiment: • the flow rates on both fluid sides of the exchanger are set at constant predetermined values. • Once the steady – state conditions are achieved, fluid temperatures upstream and downstream of the test section on both fluid sides are measured. • The upstream pressure and pressure drop across the core on the unknown side are also recorded to determine the friction factors. • The tests are repeated with different flow rates on the unknown side to cover the desired range of Reynolds number for the j vs. RE characteristics.
  39. 39. Heat capacity ratio For an unmixed – unmixed crossflow exchanger, the relationship will be:
  40. 40. For Cr 0, the heat capacity rate is determined from the measured mass flow rate on each fluid side and the specific heats of the fluids at their average temperatures. On the known side, the fluid properties are evaluated at the average temperature Ts. On the unknown side, the fluid properties are evaluated at the log-mean temperature.
  41. 41. The overall heat transfer coefficient Ua based on the total airside surface area Aa is then evaluated from NTU as The overall heat transfer coefficient Ua is considered as having three components in series: • Air side thermal resistance, including the extended surface efficiency • Wall thermal resistance • Steam side thermal resistance, including the extended surface efficiency
  42. 42. Then The test cores are generally new, and no fouling or scale resistance is on either side, so the corresponding resistance is not included above. The liquid side heat transfer coefficient must also be evaluated separately for each core and should be known a priori. However, the liquid side resistance is generally a very small percentage of the total resistance, and a reasonable estimate will suffice.
  43. 43. The term in equation 1.3 is the extended surface efficiency of the air side surface and is related to the fin efficiency of the extended surface by the following formula:
  44. 44. For many plate fin surfaces, the relation for the straight fin with constant conduction cross section may be used to a good approximation. In that case: Once the surface area and the geometry are known for the extended surface, h and are computed iteratively from equations 1.3 to 1.5.
  45. 45. The Stanton number St and the Colburn factor j are then evaluated from their definitions: The Reynolds number on the unknown side for the test point is determined from its definition: G= ρ V
  46. 46. Determination of the factor is made under steady fluid flow rates. For a given fluid flow rate on the unknown f side, the following measurements are made: 1. Core pressure drop 2. Core inlet pressure and temperature 3. Core outlet temperature 4. Fluid mass flow rate 5. Core geometrical properties.
  47. 47. Here Kc and Ke are sudden contraction and expansion pressure loss coefficients presented in Appendix 1. Tests are repeated with different flow rates on the unknown side to cover the desired range of the Reynolds number. The Reynolds number is determined in the same way as described in determination of the airside film coefficient h.
  48. 48. Liquid Flow System • Stainless steel piping • Gear pump • Resistive Heater (Watlow®) • Mass flow rate meter (D25 MicroMotion®) • Thermocouple (type T) x 2
  49. 49. Air Sampling System Consist of • Thermocouple (type T) x 2 A type T thermocouple with a measurement range of -200 to 350 degree Celsius is placed at the entrance of the wind tunnel air outlet. And for the air outlet temperature, a similar thermocouple is place near the outlet of the heat exchanger fin.
  50. 50. Pressure Drop Measurement Consist of • Pressure differential Transducer (Validyne DP-103) x 2 To measure the pressure drop across the heat exchanger, a total of two differential pressure sensors, one upstream and one downstream, are incorporated into the flow system.
  51. 51. Schematic diagram of Test Setup 2MX1M P P T T HEAT EXCHANGER LEGENDS: PUMP MASS FLOW SENSOR FILTER HEATER T THERMOCOUPLE P PRESSURE DIFFERENTIAL SENSOR
  52. 52. Data Acquisition Data Acquisition (DAQ) Acquisition of signals &waveforms &processing the signals to obtain desired information. Laboratory Virtual Instrumentation Engineering Workbench (Labview) Graphical approach allows non-programmers to build programs simply by dragging & dropping virtual representations of familiar lab equipment.
  53. 53. Start Up Procedure Power up the DAQ unit Switch on the gear pump to start water circulation Switching on the heater after full circulation of water Set the heater to the specific heat load Start Up Labview Program Begin Data Aquisition
  54. 54. Lab Equipment DAQ with Labview Software The NUS industrial wind tunnel at Mechanical Department
  55. 55. Lab Equipment Interior of a wind tunnel The Wind turbine and motor
  56. 56. 57 4. Fouling of Heat Exchangers • Literature Survey • General Methods of Fouling • Heat Exchanger Cleaning • Detailed Analysis of Anti-Fouling Methods ▫ Air Side ▫ Water Side • Advantages and Disadvantages
  57. 57. 58 Literature Survey • Fouling is defined as the accumulation of deposits on the surface of the heat exchangers • Deposits reduce the amount of heat transfer and thus reducing the efficiency. • In most of the cases, accumulation of deposits is from the fluid itself.
  58. 58. 59 Deposition of Foulant • Region A represents the initiation of adhesion • Region B represents the steady growth of deposit on the surface. • Region C shows that a steady state is reach between deposition and removal.
  59. 59. 60 Why is Fouling bad? Fin Cooler tubes severely corroded Deposits build-up on the inside of a heat Wall thinning led to this catastrophic exchanger tube failure of an exchanger tube • Fouling is highly related to conservation of energy • Fouling decreases the efficiency leading to heavier consumption of energy. • Increase in the resistance also cause the pump to work harder.
  60. 60. 61 General Methods of Fouling • Adhesion • Particulate deposition • Corrosion
  61. 61. 62 Adhesion • physical interaction between the foulant and the heat exchanger surface. • 3 types of interaction: ▫ long range attractive forces: Van Der Waals forces ▫ Bridging effect: mutual diffusion between substances of the particle and the surface ▫ short range forces: adhesion at molecular level such as hydrogen bonds and other chemical bonding
  62. 62. 63 Particulate Deposition • Particle arriving at a surface can be by two mechanism: ▫ gravitational and: stationary fluids ▫ particle transport within a fluid as it moves across the surface onto which the particles deposit: Moving fluid • transported by either or both of the following mechanism: ▫ Brownian motion and ▫ turbulent diffusion
  63. 63. 64 Corrosion • Corrosion means the breaking down of essential properties in a material due to chemical reactions with its surroundings • origin of the corrosion is the fluid itself • or a constitute of it: impurities • Corrosion process is often accelerated by the presence of scales or other deposit • corrosion could also form a protection layer (oxide layer)
  64. 64. 65 Heat Exchanger Cleaning • Circulation of Sponge Rubber Balls • Brush and Cage System • Air and Gas Injection • Magnetic Devices • Soot Blower • Water Washing • Galvanic Protection
  65. 65. 66 Circulation of Sponge Rubber Balls • Sponge rubber balls which are slightly larger (by 2mm) then the diameter of the condenser tubes are being circulated to remove precipitates. • Different types of sponge balls are available to suit different heat exchanger e.g. rubber balls coated with a layer of carborundum can be used for more heavy duty application. • The automatic cleaning system is being controlled by a Programmable Logic Controller. • The system requires a source of water which has pressure higher than the cooling water in the condenser inlet. This water is used for soaking the balls and injecting them into the Cleaning Systems.
  66. 66. 67
  67. 67. 68 Brush and Cage System • The operating method of this system is very similar to that of the Sponge rubber Ball. • It involves the use of a brush, made of wire or polymer filament fitting into the size of the condenser tube. • The brush is made to oscillate from end to end of the condenser tube to remove the deposit by abrasion. • The cage is located at the end of the tube to catch the brush after cleaning. • The addition of the brush and cage create restriction in the flow, increasing the pressure drop across the condenser. • The other drawback of this system is that the reversal of the brush would cause instability in the flow thus affecting the heat transfer process.
  68. 68. 69 Air and Gas Injection • Air and gas injection is usually used in areas where accessibility is difficult e.g. shell side of shell and tube heat exchanger. • The injection of air reduces the formation of deposits on the heat transfer surfaces. • The surge of air creates a region of high turbulence near the wall. • This method is ineffective against deposits that requires higher amount of force to remove. • Extreme care has also to be taken when the process liquid is volatile in nature; this is to avoid possibilities of forming explosive mixtures.
  69. 69. 70 Magnetic Device • The main application of magnetic devices is to eliminate scale formation in pipes. • It is could be supposed that slight soluble compounds such as calcium carbonate (exist in water as charged ion), could be affected by the application of an electric field. • One example is the use of hard water to rinse the treated steel where the hard water could give rise to precipitation of calcium phosphate and consequent scale formation. • Till date, this method is still not very commonly use and there are still doubts and critics on this method.
  70. 70. 71 Soot Blower • The fundamental of the soot blower is to remove soot that is built up in steam boiler. • Steam is channeled to the soot blower pipeline and a drain valve will drain off any water in the steam (Ensures that steam is dry). • The drain valve is shut off, and the soot blower is turned on. • The steam shoots out from the soot blower tube that is inside the boiler fireside. Many small holes for the steam to emerge are drilled along the length of the tube. • As the tube rotates, the position of the steam jet will also move with it. After a full rotation, all the areas around the soot blower tube should be clear of soot. After completing the soot blowing, the steam supply is shut off again.
  71. 71. 72
  72. 72. 73 Water Washing • Water washing of heat exchanger is the process of introducing jets of water into the system. This has been in practice over many years and is one of the most commonly applied techniques in cleaning of heat exchanger. • It is important to note that the water used in this technique is to be as pure as possible as any particle in the water could deposit itself in the process; increasing the foulant amount. • The jets are introduced intermittently and the turn off of this method could be that the thermal shock from such action could cause cracking and subsequent spalling of the foulant.
  73. 73. 74 Galvanic Protection • Galvanic protection involves the study of electric current that is involved in the corrosion of metal. • By understanding how electric current is involve in corrosion of metal, we look at various methods applied in the industry to tackle corrosion problem. • Methods of Galvanic protection include ▫ Cathodic Protection ▫ Sacrificial Anode Technique ▫ Impressed Current Technique ▫ Anodic Protection.
  74. 74. 1. fouling deposit provides additional thermal resistance to heat transfer besides those originally present due to the inherent design of the heat exchanger 2. flow area is decreased and most foulant, having a rough surface will result in an increased pressure drop through the exchanger
  75. 75. • increased capital investment • additional operating costs • loss of production • cost of remedial action
  76. 76. thermal resistance Rf across a solid barrier is given by l is the solid thickness and kf is its thermal conductivity heat flux q is given by ∆T is the change in temperature
  77. 77. • boundary layers, situated between the deposits and the fluids, provide small amount of thermal resistance to heat flow due to their almost stagnant mode • metal partition wall has good thermal conductivity, negligible temperature change at T3 and T4 • foulants have low thermal conductivities, large temperature differences required to transmit heat across these depositions
  78. 78. we can write Rf in terms of the overall heat transfer coefficient for fouling Uf general formulas for overall heat transfer coefficient, including the fouling factor, at the air and water side are respectively
  79. 79. • Besides increasing the thermal resistance, foulant layer have two additional negative effects • Firstly, once deposit reaches a significantly large thickness, cross- sectional area for fluid flow reduced • For the same volume flow, due to a smaller area, fluid velocity will have to increase and for identical conditions the Reynolds number will increase • Secondly, increase in roughness of deposit surface results in higher turbulence level, and eventually a greater amount of heat transfer
  80. 80. (three fundamental stages that describe process of deposition) 1. The diffusional transport of the foulant across the boundary layers beside the solid surface within the moving fluid. 2. Adhesion of deposit both to the surface and to itself. 3. The removal of deposit from the surface.
  81. 81. By combining these three components, rate of deposition growth can be defined as the difference between the rates of foulant deposition and removal
  82. 82. • A = straight line relationship, deposit thickness increases at a constant rate with time after the initial adhesion period • B = falling rate of deposition thickening with time • C = asymptotic curve like curve B at the beginning but reaches final plateau steady state or asymptote (rate of deposition = rate of removal)
  83. 83. Change in Heat Transfer Coefficient Change due to Change due to Change due to change in roughness of thermal resistance of Re caused by presence foulant foulant of foulant
  84. 84. 85 Detailed Analysis of Anti-Fouling Methods : Air Side : Sonic Technology • Similar to vibration caused by sound energy to dislodge the deposits off metal surfaces • Device for producing the sonic wave can a sonic horn, usually operating at audible frequency of approximately 220 Hertz with intensity of about 130 decibels • Low frequency resonant sound ranging from 0 to 20 Hertz capable of setting up sound field to remove soot, loose and brittle dust particles in the air side of heat exchanger
  85. 85. Sonic Technology (cont’) • commercially available sonic horn model #CS-125 designed by IAC (Industrial Accessories Company) • capable of removing build-up particulates using a fundamental frequency of 125 Hertz and SPL (Sound Pressure Level) of 146 decibels, operating at 10 seconds every 5 to 10 minute interval • cleaning device can be used to clean agglomerated dust on collector plates of an electrostatic precipitator, which is similar in structure to a plate fin heat exchanger
  86. 86. Corona Discharge • ionizes the fluid so as to create a plasma around the electrode • may be positive or negative • Neutralises static charges on the surfaces of the heat exchanger’s plate fins • Benefit of keeping the fin surfaces neutral in charge
  87. 87. 88 Water Side : Electronic Anti- Fouling Technology • Most prominent is formation of scales • Hard water is heated • Degradation in the performance • Decrease the flow rate or increase the pressure drop • Solution :Electronic Anti-fouling technology
  88. 88. Electronic Anti-fouling technology Overview of Electronic Anti-fouling technology
  89. 89. Electronic Anti-fouling technology • Induced electric field to increase the ions and crystals collision frequency • Produces a pulse input current to create time-varying magnetic fields inside the pipe Cross section of pipe where induced electric field oscillates with time
  90. 90. Electronic Anti-fouling technology • Resulting in collision, precipitation as well as coagulation. • Converted into insoluble mineral crystals of submicron sizes, easily removed • Level of Super-saturation of the water will decrease • Scale-causing mineral ions and particles were eliminated from the water
  91. 91. Electronic Anti-fouling technology Pressure drop across HE for 4 different cases
  92. 92. Electronic Anti-fouling technology Overall Heat Coefficient Fouling factors
  93. 93. 94 Conclusion and Recommendations ▫ Conclusions  Heat Exchanger Model for Experiment  Proposed Experiment  Fouling of Heat Exchanger ▫ Recommendations for Future Work
  94. 94. 95 Conclusions : Heat Exchanger Model for Experiment • Manufacturability constrains. • If we are to scale down the hydraulic diameter, Dh, by a desired scaling factor, it’s almost impossible to fabricate such small passage. • We suggest to build a smaller heat exchanger keeping the geometrical data (Dh) unchanged. From this smaller size prototype, • Two most important date: Heat transfer coefficient h, which relates to the Stanton number St and the Colburn factor j, and the flow friction factor f, necessary for pressure drop analysis. • After obtaining the experimental h and f, the rating of heat exchanger procedure can then be applied to calculate the experimental heat load Q and pressure drop ∆P. • Furthermore, if manufacturability is not an issue, the hydraulic diameter of the chosen fin type may be varied and better h and f can be obtained.
  95. 95. 96 Conclusions : Proposed Experiment • By using the experimental results, we are able to determine Stanton number St, Colburn factor j and the Reynolds number . • This will enable us to find out the Q heat load of the experimental heat exchanger, and based on this heat load we can compare it with the heat load derived from the excel spread sheet calculation.
  96. 96. 97 Conclusions : Fouling of Heat Exchanger • With innovative methods employed on the air side and water side of the heat exchanger • We can be confident that fouling can be reduced, or even eliminated. • The use of sonic vibrations, coupled with the phenomena of corona discharged air ions will safely prevent the buildup of dust particles on the plate-fin surfaces. • As for the water side, experiments have been conducted to validate the theory being • The downtime of the wind turbine can also be reduced and maintenance can be done online.
  97. 97. 98 Conclusions : Recommendations for Future Work • With the stage set for the experiment to be conducted, our future juniors undertaking this project can carry on from where we last left off. • The theory of the scaling laws can also be further analyzed and researched in a much deeper scope. • Feasibility study regarding the innovative method of anti-fouling for the air and water side of the heat exchanger can also be conducted • Purchase the equipment and implement it on a real heat exchanger. • End result will be very beneficial to the industry and will indeed benefit the future generations to come. • On this note, there are still many areas of this project that has the potential for future advancement.
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