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Registered: ‎02-04-2013

Heat exchanger (helical)

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04-26-2013 06:25 AM

Hello Colleagues, 

 

I am trying to simulate  a helical heat exchanger, simulation is working fine however when I compare my SIM CFD results to theory/empirical solution I found it way off (so model not validated).

 

I am interested in a transient solution so I have tried to make the time step smaller and mesh size as well and still solution was still off. I rechecked my theoratical solution which was based on an example from a book there was nothing wrong and the only modification I made to simplify the CFD work is: I reduced the mass flow rate of both fluid in the shell and the helical tube and I played with the desired output and input temperautres to make heat exchanger compact so it wont take as much time to solve.

 

In autodesk CFD SIM: As i said it is a transient problem although I have tried steady state and solution was aslo different from both theory and the transient results. I advection 5 and solution controls where kept at default, turbulence default (K-epsilon),  timestep size 0.05 and I also tried 0.1, mesh size: I had 1 million, 2 million, and 4 million elment cases. 

 

I would appreciate any suggestions and or any resources you think could be helpful to solve my problem.

 

Note that I have 

 

Thank you, 

 

Ghaleb 

Product Support
662 Posts
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Registered: ‎08-24-2011

Re: Heat exchanger (helical)

04-26-2013 08:44 AM in reply to: ghalebsater

What type of fluid do you have going through the HX?

 

How much error did you have with your steady state solution?  I would not go to the transient setup until you have a good steady state solution.

 

-Royce



Royce Abel
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Re: Heat exchanger (helical)

04-26-2013 09:26 AM in reply to: Royce_adsk

Hello Royce, 

I am interested in the transient solution more, anyhow as per your suggestion let me share with you the steady state problem first and then if possible we go to transient. 

 

I have defined two liquids, A and B see properties below. The coil is made of stainless steel.  The cfz file for this case is too large to attach here. 

 

My error for steady state is: % error of temperature of fluid A exiting coil = 41% and % error of temperature of fluid B exiting shell is around 76%.

 

CFD results: Steady: coil ( Tout: 70 degree C) and shell (Tout: 44 degree C).

Theory results: coil ( Tout: 120 degree C) and shell (Tout: 25 degree C).

In shell 

Liquid B properties:

density: 935 kg/m^3 

Mass flow rate: 0.138 kg/sec

Viscosity: 0.0016 Pa-s

Specific heat: 4183.995 J/Kg-k

Thermal Conductivity:0.4739225 W/m.k

Tin=  5 degree C 

Tout = 25 degree C 

 

and liquid A in coil:

 

density: 870 kg/m^3 

Mass flow rate: 0.088 kg/sec

Viscosity: 0.000525 Pa-s

Specific heat: 4183.995 J/Kg-k

Thermal Conductivity:0.4812 W/m.k

 

Tin=  140 degree C 

Tout = 120 degree C 

 

Product Support
662 Posts
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Registered: ‎08-24-2011

Re: Heat exchanger (helical)

04-28-2013 08:06 AM in reply to: ghalebsater
Do you have access to 2014? It might be that you need the SST turb model to accurately capture the heat transfer more accurately.


Royce Abel
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Registered: ‎02-04-2013

Re: Heat exchanger (helical)

04-28-2013 08:55 AM in reply to: Royce_adsk

Unfortunately I don't have access to 2014 issue.

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Registered: ‎02-04-2013

Re: Heat exchanger (helical)

04-29-2013 12:39 PM in reply to: Royce_adsk

I am going to try to run different simualtions using the given turbulent model in 2013 version. This version should be able to simulate this problem with a much lower error from what I am seeing now.

 

I would appreciate if you have any other suggestions that I could try as well.