Download - Heat Exchanger Performance
![Page 1: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/1.jpg)
HEAT EXCHANGERAhmed Ragab
![Page 2: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/2.jpg)
AGENDATerminologyHeat exchanger designHeat exchanger performance
Increasing Heat Exchanger Performance
![Page 3: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/3.jpg)
TERMINOLOGY USED IN HEAT EXCHANGERS
Capacity ratio:Ratio of the products of mass flow rate and specific heat capacity of the cold fluid to that of the hot fluid.
Also computed by the ratio of temperature range of the hot fluid to that of the cold fluid.
Higher the ratio greater will be size of the exchanger
![Page 4: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/4.jpg)
Effectiveness: Ratio of the cold fluid temperature range to that of the inlet temperature difference of the hot and cold fluid.
Higher the ratio lesser will be requirement of heat transfer surface.
![Page 5: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/5.jpg)
Overall Heat transfer Coefficient :The ratio of heat flux per unit
difference in approach across a heat exchange equipment considering the individual coefficient and heat exchanger metal surface conductivity.
The magnitude indicates the ability of heat transfer for a given surface.
Higher the coefficient lesser will be the heat transfer surface requirement
![Page 6: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/6.jpg)
Temperature Approach :The difference in the temperature between the hot and cold fluids at the inlet / outlet of the heat exchanger.
The greater the difference greater will be heat transfer flux
![Page 7: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/7.jpg)
HEAT TRANSFERThe rate equation for heat transfer is:Q = U × A × F × (LMTD)
where:Q = Heat duty, Btu/hrU = Overall heat transfer coefficient,
Btu/(hr × °F × ft2)A = Heat transfer area, ft2MTD = Mean temperature difference, °F
![Page 8: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/8.jpg)
MEAN TEMPERATURE DIFFERENCEFor co-current flow:LMTD = [(Ti-to)-(To-ti)] / ln [(Ti-to)/(To-ti)]
Where:Ti = Hot stream inlet temperature, °FTo = Hot stream outlet temperature, °Fti = Cold stream inlet temperature, °Fto = Cold stream outlet temperature, °F
![Page 9: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/9.jpg)
OVERALL HEAT TRANSFER COEFFICIENT1/U = (1/hi + Rfi)(Ao/Ai) + Rw + 1/ho + Rfowhere: hi = Inside film coefficient, Btu/hr × °F × ft2 Rfi = Inside fouling resistance, hr × °F ×
ft2/Btu Ao = Outside area, ft2 Ai = Inside area, ft2 Rw = Tube wall resistance, hr × °F × ft2/Btu ho = Outside film coefficient, Btu/hr × °F ×
ft2 Rfo = Outside fouling resistance, hr × °F ×
ft2/Btu
![Page 10: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/10.jpg)
THE TUBE WALL RESISTANCEThe tube wall resistance is given by:
where:do = Tube O.D., inchesdi = Tube I.D., incheskw = Tube wall thermal conductivity,
Btu/hr × °F × ft
![Page 11: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/11.jpg)
HEAT EXCHANGER PERFORMANCE
Methodology of Heat Exchanger Performance
Assessment
Procedure for determination of Overall heat transfer Coefficient,
U at field
![Page 12: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/12.jpg)
Step – A Monitoring and reading of steady state parameters of
the heat exchanger under evaluation are tabulated as below:
![Page 13: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/13.jpg)
Step – B With the monitored test data, the physical properties of the stream can be tabulated as required for the evaluation of the thermal data
![Page 14: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/14.jpg)
Step – C Calculate the thermal parameters of heat exchanger and compare with the design data
![Page 15: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/15.jpg)
Step – D The following formulae are used for
calculating the thermal parameters:
1. Heat Duty, Q = qs + ql
Where, qs is the sensible heat and ql is the
latent heat For Sensible heat qs = Wx Cph x(Ti- To)/1000/3600 in kW (or) qs = w x Cpc x (to-ti)/1000/3600 in kW
![Page 16: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/16.jpg)
For Latent heat ql= W x λh ,
λh – Latent heat of Condensation of a hot condensing vapor
(or)
ql = w x λc , where λc - Latent heat of Vaporization
![Page 17: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/17.jpg)
2. Hot Fluid Pressure Drop, ΔPh = Pi – Po
3. Cold fluid pressure drop, ΔPc = pi- po
4. Temperature range hot fluid, ΔT = Ti- To
5. Temperature range cold fluid, Δt = to – ti
![Page 18: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/18.jpg)
6. Capacity ratio, R = W x CPh / w x Cpc (or)
(Ti- To) / (to- ti)
7. Effectiveness, S = (to- ti) / (Ti – ti)
![Page 19: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/19.jpg)
EXAMPLES
Liquid – Liquid Exchanger A shell and tube exchanger of following configuration
is considered being used for oil cooler with oil at the shell side and cooling water at the tube side.
Tube Side
460 Nos x 25.4mmOD x 2.11mm thick x 7211mm long
Pitch – 31.75mm 30o triangular
2 Pass
![Page 20: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/20.jpg)
Shell Side
787 mm ID
Baffle space – 787 mm
1Pass
![Page 21: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/21.jpg)
The monitored parameters are as below:
![Page 22: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/22.jpg)
Calculation of Thermal data: Heat Transfer Area = 264.55 m2
1. Heat Duty:
Q = qs + ql
Hot fluid, Q = 719800 x 2.847 x (145 –102) /3600 = 24477.4 kW
Cold Fluid, Q = 881150 x 4.187 x (49 – 25.5)
3600
=24083.4 kW
![Page 23: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/23.jpg)
2. Hot Fluid Pressure Drop Pressure Drop = Pi – Po = 4.1 – 2.8 = 1.3 bar g.
3. Cold Fluid Pressure Drop
Pressure Drop = pi – po = 6.2 – 5.1 = 1.1 bar g.
4. Temperature range hot fluid
Temperature Range ΔT = Ti – To = 145 – 102 = 43 o C.
5. Temperature Range Cold Fluid
Temperature Range Δt = to – ti = 49 – 25.5 = 23.5 0C.
![Page 24: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/24.jpg)
6. Capacity Ratio Capacity ratio, R = (Ti-To) / (to-ti) = 43 =
1.83 23.5
7. Effectiveness
Effectiveness, S = (to – ti) / (Ti – ti) =(49 – 25.5)/(145-25.5) =23.5/119.5 = 0.20.
![Page 25: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/25.jpg)
8. LMTD a) LMTD, Counter Flow = (96 – 76.5)/ ln (96/76.5) = 85.9
0C. b) Correction Factor to account for Cross flow
F = 0.977.
9. Corrected LMTD
= F x LMTD = 0.977 x 85.9 = 83.9 oC.
10. Overall Heat Transfer Co-efficient
U = Q/ A ΔT = 24477.4/ (264.55 x 83.9) = 1.104 kW/m2. K
![Page 26: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/26.jpg)
COMPARISON OF CALCULATED DATA WITH DESIGN DATA
![Page 27: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/27.jpg)
CONDENSER EXAMPLE 2
![Page 28: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/28.jpg)
INCREASING HEAT EXCHANGER PERFORMANCE
1.Finning2.Tube Inserts3.Tube Deformation
![Page 29: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/29.jpg)
Finning
Tubes can be finned on both the interior and exterior. This is probably the oldest form of heat transfer enhancement.
Finning is usually desirable when the fluid has a relatively low heat transfer film coefficient as does a gas.
The fin not only increases the film coefficient with added turbulence but also increases the heat transfer surface area.
![Page 30: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/30.jpg)
Tube Inserts Inserts, turbulators, or static mixers are
inserted into the tube to promote turbulence. These devices are most effective with high viscosity fluids in a laminar flow regime
Increases in the heat transfer film coefficients can be as high as five times.
![Page 31: Heat Exchanger Performance](https://reader034.vdocument.in/reader034/viewer/2022042504/577cc3b01a28aba71196dcdb/html5/thumbnails/31.jpg)
Tube Deformation
Many vendors have developed proprietary surface configures by deforming the tubes. The resulting deformation appears corrugated, twisted, or spirally fluted.