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Conjugate heat transfer and non-isothermal fluid flow

Posted Feb 14, 2011, 9:22 a.m. EST Fluid & Heat, Heat Transfer & Phase Change Version 4.2a 8 Replies

Ali Masabai
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Hi

I am trying to simulate a fluid flow in a pipe and this pipe inside cubic box and this box is subjected to heat flux at upper half. I have turbulent flow. The heat transfer from the solid cubic box to the solid pipe to the fluid. I have two basic questions.


What is the different between Conjugate heat transfer and?non-isothermal fluid flow ??I believe that the conjugate heat transfer should selected when the heat transfer from solid to fluid. Please correct me if I am wrong

The second question I tried both of conjugate and non-isothermal fluid but the fluid temperature at the exit is around 450 c (inlet temperature is 400 c) although the pipe surface temperature is around 1600C. It should be more than that

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8 Replies Last Post May 23, 2011, 11:08 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 15, 2011, 2:20 a.m. EST
Hi

when I run it I get far more at the output (I'm using 4.1.0.154 and I remeshed in normal "physics induced default mesh"

--
Good luck
Ivar
Hi when I run it I get far more at the output (I'm using 4.1.0.154 and I remeshed in normal "physics induced default mesh" -- Good luck Ivar
Ali Masabai
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Posted: 1 decade ago Feb 15, 2011, 4:20 a.m. EST
HI


The same results I got please note that temperature unit in keliven , so the inlet tempearute is 673K and the output in the range of 673K to 800K. I think something wrong


By the way how I can calculate the output temperature with comsol . I tried to intergatea the area but the reuslt was wrong
HI The same results I got please note that temperature unit in keliven , so the inlet tempearute is 673K and the output in the range of 673K to 800K. I think something wrong By the way how I can calculate the output temperature with comsol . I tried to intergatea the area but the reuslt was wrong
Ali Masabai
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Posted: 1 decade ago Feb 15, 2011, 8:51 a.m. EST
Hi

I am sorry to ask this question agian but I really need some help


Fluid temperature at the exit is slightly change which l is annoying me . I am feeling there is a problem when the heat transfer from the solid domain to the fluid domain
Hi I am sorry to ask this question agian but I really need some help Fluid temperature at the exit is slightly change which l is annoying me . I am feeling there is a problem when the heat transfer from the solid domain to the fluid domain
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 15, 2011, 9:26 a.m. EST
Hi

I do not have enough free time to reply just now, but clearly from the profile that I got by using a cut line on the outlet you have a steep gradient, so your fluid has a low heat conduction, or a high speed ;)

to calculate the average temperature you use the average operator on the outlet surface, but I beleive the T proile is more interesting. You add a Data set by right clicking on the data set node

--
Good luck
Ivar
Hi I do not have enough free time to reply just now, but clearly from the profile that I got by using a cut line on the outlet you have a steep gradient, so your fluid has a low heat conduction, or a high speed ;) to calculate the average temperature you use the average operator on the outlet surface, but I beleive the T proile is more interesting. You add a Data set by right clicking on the data set node -- Good luck Ivar
Ali Masabai
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Posted: 1 decade ago Feb 17, 2011, 11:37 a.m. EST
I am sorry to bring it up again, but I really do need help

I tried what you said and I reduced the inlet velocity to 0.5 m/s but this did solve the problem. The thermal conductivity for the fluid is around 0.4 W/(K•m). which not that bad.

I just want to make sure that am I using the right boundary condition

Non-isothermal Turbulent flow

Boundary conditions for heat transfer

Temperature 400C
Outflow
Heat flux 1400000w/m2 (at the upper area)

Boundary conditions for Turbulent flow
I
nlet: velocity, Normal inflow velocity 0.5 m/s
Outlet: Pressure, no viscous stress
I am sorry to bring it up again, but I really do need help I tried what you said and I reduced the inlet velocity to 0.5 m/s but this did solve the problem. The thermal conductivity for the fluid is around 0.4 W/(K•m). which not that bad. I just want to make sure that am I using the right boundary condition Non-isothermal Turbulent flow Boundary conditions for heat transfer Temperature 400C Outflow Heat flux 1400000w/m2 (at the upper area) Boundary conditions for Turbulent flow I nlet: velocity, Normal inflow velocity 0.5 m/s Outlet: Pressure, no viscous stress
Ozgur
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Posted: 1 decade ago Feb 17, 2011, 12:45 p.m. EST
Here is a suggestion. Use engineering correlations to calculate expected heat transfer coefficient based on Re & Pr numbers and then solve a simple problem that is similar enough to your situation (e.g. with constant wall temperature of 1600 C ) analytically. You might be surprised to find out that your liquid temperature increase really is small. Be careful to make the distinction between local and mass flow averaged fluid temperatures.
hope this helps
Ozgur
Here is a suggestion. Use engineering correlations to calculate expected heat transfer coefficient based on Re & Pr numbers and then solve a simple problem that is similar enough to your situation (e.g. with constant wall temperature of 1600 C ) analytically. You might be surprised to find out that your liquid temperature increase really is small. Be careful to make the distinction between local and mass flow averaged fluid temperatures. hope this helps Ozgur
Michael Bates
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Posted: 1 decade ago Feb 28, 2011, 12:21 p.m. EST
"Here is a suggestion. Use engineering correlations to calculate expected heat transfer coefficient based on Re & Pr numbers and then solve a simple problem that is similar enough to your situation (e.g. with constant wall temperature of 1600 C ) analytically. You might be surprised to find out that your liquid temperature increase really is small. Be careful to make the distinction between local and mass flow averaged fluid temperatures.
hope this helps
Ozgur"

Hi - I would agree with this approach and if you need assistance running these numbers please contact me through our website

We're working on a live calculator for our website but in the meantime I'd be happy to help you out

Michael Bates
Technical Director
Duratherm Heat Transfer Fluids
"Here is a suggestion. Use engineering correlations to calculate expected heat transfer coefficient based on Re & Pr numbers and then solve a simple problem that is similar enough to your situation (e.g. with constant wall temperature of 1600 C ) analytically. You might be surprised to find out that your liquid temperature increase really is small. Be careful to make the distinction between local and mass flow averaged fluid temperatures. hope this helps Ozgur" Hi - I would agree with this approach and if you need assistance running these numbers please contact me through our website We're working on a live calculator for our website but in the meantime I'd be happy to help you out Michael Bates Technical Director Duratherm Heat Transfer Fluids
Michael Bates
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Posted: 1 decade ago May 23, 2011, 11:08 a.m. EDT
Hello, just thought I'd update... our calculator is now online if anyone is looking for some quick heat transfer coefficient numbers, including, pressure drops, Reynolds, Prandtl and Nusselt

www.heat-transfer-fluid.com/resources/heat-transfer-coefficient-calculator.php

Michael Bates
Technical Director
Duratherm Heat Transfer Fluids
www.heat-transfer-fluid.com

Hello, just thought I'd update... our calculator is now online if anyone is looking for some quick heat transfer coefficient numbers, including, pressure drops, Reynolds, Prandtl and Nusselt http://www.heat-transfer-fluid.com/resources/heat-transfer-coefficient-calculator.php Michael Bates Technical Director Duratherm Heat Transfer Fluids www.heat-transfer-fluid.com

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