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CFD Simulations in Ansys CFX of Plate Heat Exchanger Channels using Fanning Friction Factor and Nusselt Number

Svensson, Simon LU (2018) KETM05 20181
Chemical Engineering (M.Sc.Eng.)
Abstract
In this master thesis computational fluid dynamic simulations of two plate heat exchanger channels have been performed in Ansys CFX. The full geometry of the channels has not been included, the channels were modeled with a flat geometry instead of a corrugated pattern. To account for the effect of the corrugation on the pressure drop, one-time pressure losses and momentum sources were added in the model. The momentum sources were related to the Fanning friction factor, which in turn was related to the Reynolds number by experimental correlations provided by Alfa Laval. The heat transfer was modeled with a thermal contact resistance between the hot and the cold channels. The contact resistance included the heat transfer coefficient for the... (More)
In this master thesis computational fluid dynamic simulations of two plate heat exchanger channels have been performed in Ansys CFX. The full geometry of the channels has not been included, the channels were modeled with a flat geometry instead of a corrugated pattern. To account for the effect of the corrugation on the pressure drop, one-time pressure losses and momentum sources were added in the model. The momentum sources were related to the Fanning friction factor, which in turn was related to the Reynolds number by experimental correlations provided by Alfa Laval. The heat transfer was modeled with a thermal contact resistance between the hot and the cold channels. The contact resistance included the heat transfer coefficient for the hot and the cold fluid, calculated from Nusselt numbers. The Nusselt numbers were obtained from experimental correlations provided by Alfa Laval, based on values for the Reynolds number and the Prandtl number.
Three different channel designs with different geometries were simulated, and the results were compared to Alfa Laval’s design program for plate heat exchangers. Each channel design was simulated with correlations for both high theta pattern and low theta pattern for the corrugations. The resulting pressure drop for the high theta pattern was generally accurate with a maximum difference of -13% to +6% compared to the reference. For the low theta pattern the pressure drop difference varied between -20% to +13% for two of the channel designs, while the last design was more than 50% off. The reason for why the low theta pattern is harder to simulate is believed to be some problem with the momentums sources in the distribution areas of the channels. In a high theta channel, a small share of the pressure drop occurs in the distribution area resulting in a small pressure drop deviation. In a low theta channel, a major part of the pressure occurs in the distribution area, leading to larger deviations. The heat transfer was considered accurate for all channels and patterns, with a maximum deviation of 2% of the outlet temperatures.
The model can be used in early design stages of new channel geometries to give an indication of the expected performance. The model can also be used to replace detailed simulations in specific parts of the channels, while the other parts are simulated with the corrugation geometry. The model is not suitable for simulating new corrugation patterns since it is based on correlations from existing patterns. (Less)
Popular Abstract (Swedish)
Datorsimuleringar blir ett allt viktigare verktyg för att förstå, utveckla och effektivisera alla sorters processer och produkter i vårt samhälle. Det är ofta svårt att exakt efterlikna verkligheten, och för att göra simuleringarna möjliga används ofta modeller som förenklar verkligheten.
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author
Svensson, Simon LU
supervisor
organization
course
KETM05 20181
year
type
H2 - Master's Degree (Two Years)
subject
keywords
CFD, chemical engineering, CFX, ANSYS, Reynolds, Prandtl, Nusselt, PHE, plate heat exchanger, heat exchanger, Alfa Laval, kemiteknik
language
English
id
8954096
date added to LUP
2018-08-03 11:22:15
date last changed
2018-08-03 11:22:15
@misc{8954096,
  abstract     = {In this master thesis computational fluid dynamic simulations of two plate heat exchanger channels have been performed in Ansys CFX. The full geometry of the channels has not been included, the channels were modeled with a flat geometry instead of a corrugated pattern. To account for the effect of the corrugation on the pressure drop, one-time pressure losses and momentum sources were added in the model. The momentum sources were related to the Fanning friction factor, which in turn was related to the Reynolds number by experimental correlations provided by Alfa Laval. The heat transfer was modeled with a thermal contact resistance between the hot and the cold channels. The contact resistance included the heat transfer coefficient for the hot and the cold fluid, calculated from Nusselt numbers. The Nusselt numbers were obtained from experimental correlations provided by Alfa Laval, based on values for the Reynolds number and the Prandtl number. 
Three different channel designs with different geometries were simulated, and the results were compared to Alfa Laval’s design program for plate heat exchangers. Each channel design was simulated with correlations for both high theta pattern and low theta pattern for the corrugations. The resulting pressure drop for the high theta pattern was generally accurate with a maximum difference of -13% to +6% compared to the reference. For the low theta pattern the pressure drop difference varied between -20% to +13% for two of the channel designs, while the last design was more than 50% off. The reason for why the low theta pattern is harder to simulate is believed to be some problem with the momentums sources in the distribution areas of the channels. In a high theta channel, a small share of the pressure drop occurs in the distribution area resulting in a small pressure drop deviation. In a low theta channel, a major part of the pressure occurs in the distribution area, leading to larger deviations. The heat transfer was considered accurate for all channels and patterns, with a maximum deviation of 2% of the outlet temperatures. 
The model can be used in early design stages of new channel geometries to give an indication of the expected performance. The model can also be used to replace detailed simulations in specific parts of the channels, while the other parts are simulated with the corrugation geometry. The model is not suitable for simulating new corrugation patterns since it is based on correlations from existing patterns.},
  author       = {Svensson, Simon},
  keyword      = {CFD,chemical engineering,CFX,ANSYS,Reynolds,Prandtl,Nusselt,PHE,plate heat exchanger,heat exchanger,Alfa Laval,kemiteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {CFD Simulations in Ansys CFX of Plate Heat Exchanger Channels using Fanning Friction Factor and Nusselt Number},
  year         = {2018},
}