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Heat Exchanger Simulation with helically corrugated tube.

Question asked by Vamsi Mokkapati on Mar 27, 2013
Latest reply on Mar 30, 2013 by Jared Conway

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Hi all,

I was trying to do the shell and tube heat exchanger simulation using solidoworks, here the tube side of the heat exchanger is not a plain tube, its a helically corrugated tube instead. I followed the similar procedure of the tutorial given in the solidoworks flow simulation, but seems there is something wrong and I couldn't figure it out. but the results are very unlikely, for example the density of the gas which is flowing in the corrugated tube is some where around 900kg/m^3. when I have done the plain tube and shell heat exchanger the results were close to the results of the experimental setup.

The fluid flowing inside the tube is air with the inlet mass flowrate of 0.05kg/s at 700K, the fluid inside the shell is water and is flowing at 0.1kg/s at 300K. The default fluid that I selected for the project is water and hence I defined the fluid subdomain inside the corrugated tube as air and assigned the inlet boundary conditions to it. The outlets of the both air air and water are set to be at environmental pressure and temperature since they are unknowns.

please find the attached heat exchanger file in this discussion.

Jared Conway Mar 28, 2013 9:10 PM

Correct Answer

Hi Vamsi, just running the model now.

Can you elaborate on what the results should be? Can you share the model with the straight tube and point out the differences between the 2 models? (both setup and results)

A few comments on the setup that I can see:

1. adiabatic wall, is it really 100% adiabatic on the outside? perfectly insulated?

2. i prefer to make lids myself rather than using the lid tool. this makes sure that any interferences that are found are ones that i want to eliminate. i haven't had a chance to fully check your model for interferences..etc.

3. i don't think you need to have the initial parameter velocity in the X direction. you can use that to speed along steady state solutions but this one should solve pretty quick.

4. you can remove air from the default fluid definition. because from what i can see you want to have nitrogen in the center and water on the outside. (setup looks ok)

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Vicente EXtube.SLDPRT.zip1.0 MB

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Jared Conway Mar 28, 2013 9:10 PM

Hi Vamsi, just running the model now.

Can you elaborate on what the results should be? Can you share the model with the straight tube and point out the differences between the 2 models? (both setup and results)

A few comments on the setup that I can see:

1. adiabatic wall, is it really 100% adiabatic on the outside? perfectly insulated?

3. i don't think you need to have the initial parameter velocity in the X direction. you can use that to speed along steady state solutions but this one should solve pretty quick.

4. you can remove air from the default fluid definition. because from what i can see you want to have nitrogen in the center and water on the outside. (setup looks ok)

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Vamsi Mokkapati @ Jared Conway on Mar 29, 2013 3:11 PM

Hi Jared,

I know the inlet conditions of the fluid and gas, for example let us say I have gas at 600K and water at 300K at the inlet, if this is the case the outlet of the gas should be <600K and water >300K with variation in velocity and slight variation in the density(as the temperature varies). I have no pressure information at inlet and outlet of heat exchanger.

Reasons for your comments

1.adiabatic wall, It is not 100% adiabatic outside, not insulated at all, but at first I was trying to do it without considering the heat loss to the environmet then add the outside air condition to compare both of the results. I just want to see whether this simulation works out well or not.

2.I tried by making own lids also, but anyway I tested with floexpress to see whether the design has any problems.

3.I haven't specified any velocity in the X direction, It automatically takes this because I gave the inlet mass flow rate.

4.I did even without the air.

The major problem that I found is when I specify the fluid subdomain as water which is flowing outside, calculation shows the density of the inside fluid is also close to density of the water, but when I specify air in the fluid subdomain, the calculation shows the density of the outside fluid close to that of the density of Air.

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Jared Conway Mar 29, 2013 11:11 AM

the results look pretty reasonable to me. the temperature drop in the inner fluid is about 60degrees. what are you expecting?

a couple other things I noticed on review of the results:

1. few goals, i would recommend setting up some "smoke test" goals where you check mass flow rate in and out. similarly things like inlet/outlet pressure and temperature. I prefer goals because it lets me evaluate many parameters at once on many locations at once rather than surface parameters that are surface by surface.

2.did you mean to set environmental pressure? since they are set at the outlets, this will define static pressure at the outlet. Are the inlet pressures ok?

3.I noticed you used level 8 mesh. did you see a difference from 3-8? you might want to try solution adaptive for your final runs.

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Vamsi Mokkapati @ Jared Conway on Mar 29, 2013 3:15 PM

the temperatures of my results are also reasonable but have you gone through the other parameters like density and Velocity??

Inlet and outlet densities of water and air?? If so can you tell me what are values you got?

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Jared Conway @ Vamsi Mokkapati on Mar 29, 2013 4:55 PM

density of water is 995,

default fluid is nitrogen, it's 0.75 at the inlet, 0.63 at the outlet

all in kg/m^3

looks good to me

checked nitrogen here: http://yeroc.us/calculators/gas-density.php

130kPa, 600K and 28g/mol

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Vamsi Mokkapati @ Jared Conway on Mar 29, 2013 5:34 PM

Thats great.. Looks like what I need, Can you tell me what all changes you made to the model that I have sent??

What's the version you used to simulate it?

Can you send the file please, @vsmokkapati@alaska.edu

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Jared Conway @ Vamsi Mokkapati on Mar 29, 2013 5:49 PM

I'm running 2013 sp2.0, what version are you running?

I made no changes. Just looked at the setup and ran. Actually I changed from mesh level 8 to 5. Maybe yours completed because of max travels rather than converged goals and that is why your results are wrong. Try level 3 and then 5. Check why completion occurs.

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Vamsi Mokkapati @ Jared Conway on Mar 29, 2013 6:35 PM

I tried this is 2011 and 2012 version, but gives me same higher density values..

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Jared Conway @ Vamsi Mokkapati on Mar 30, 2013 12:49 PM

Thats at 25 iterations, have you let it run to completion?

Please setup goals for pressure, temp, density and velocity all all the inlets and outlets, let it run to completion and post.

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9 Replies

Jared Conway Mar 28, 2013 9:10 PM
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Correct Answer
Hi Vamsi, just running the model now.

Can you elaborate on what the results should be? Can you share the model with the straight tube and point out the differences between the 2 models? (both setup and results)

A few comments on the setup that I can see:
1. adiabatic wall, is it really 100% adiabatic on the outside? perfectly insulated?
2. i prefer to make lids myself rather than using the lid tool. this makes sure that any interferences that are found are ones that i want to eliminate. i haven't had a chance to fully check your model for interferences..etc.
3. i don't think you need to have the initial parameter velocity in the X direction. you can use that to speed along steady state solutions but this one should solve pretty quick.
4. you can remove air from the default fluid definition. because from what i can see you want to have nitrogen in the center and water on the outside. (setup looks ok)
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- Vamsi Mokkapati @ Jared Conway on Mar 29, 2013 3:11 PM
  Mark Correct
  Correct Answer
  Hi Jared,
  
  I know the inlet conditions of the fluid and gas, for example let us say I have gas at 600K and water at 300K at the inlet, if this is the case the outlet of the gas should be <600K and water >300K with variation in velocity and slight variation in the density(as the temperature varies). I have no pressure information at inlet and outlet of heat exchanger.
  
  Reasons for your comments
  1.adiabatic wall, It is not 100% adiabatic outside, not insulated at all, but at first I was trying to do it without considering the heat loss to the environmet then add the outside air condition to compare both of the results. I just want to see whether this simulation works out well or not.
  2.I tried by making own lids also, but anyway I tested with floexpress to see whether the design has any problems.
  3.I haven't specified any velocity in the X direction, It automatically takes this because I gave the inlet mass flow rate.
  4.I did even without the air.
  
  The major problem that I found is when I specify the fluid subdomain as water which is flowing outside, calculation shows the density of the inside fluid is also close to density of the water, but when I specify air in the fluid subdomain, the calculation shows the density of the outside fluid close to that of the density of Air.
  Like • Show 0 Likes0
  Actions
Jared Conway Mar 29, 2013 11:11 AM
Mark Correct
Correct Answer
the results look pretty reasonable to me. the temperature drop in the inner fluid is about 60degrees. what are you expecting?

a couple other things I noticed on review of the results:
1. few goals, i would recommend setting up some "smoke test" goals where you check mass flow rate in and out. similarly things like inlet/outlet pressure and temperature. I prefer goals because it lets me evaluate many parameters at once on many locations at once rather than surface parameters that are surface by surface.
2.did you mean to set environmental pressure? since they are set at the outlets, this will define static pressure at the outlet. Are the inlet pressures ok?
3.I noticed you used level 8 mesh. did you see a difference from 3-8? you might want to try solution adaptive for your final runs.
Like • Show 0 Likes0
Actions
- Vamsi Mokkapati @ Jared Conway on Mar 29, 2013 3:15 PM
  Mark Correct
  Correct Answer
  the temperatures of my results are also reasonable but have you gone through the other parameters like density and Velocity??
  
  Inlet and outlet densities of water and air?? If so can you tell me what are values you got?
  Like • Show 0 Likes0
  Actions
  - Jared Conway @ Vamsi Mokkapati on Mar 29, 2013 4:55 PM
    Mark Correct
    Correct Answer
    density of water is 995,
    default fluid is nitrogen, it's 0.75 at the inlet, 0.63 at the outlet
    all in kg/m^3
    
    looks good to me
    checked nitrogen here: http://yeroc.us/calculators/gas-density.php
    130kPa, 600K and 28g/mol
    Like • Show 0 Likes0
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    - Vamsi Mokkapati @ Jared Conway on Mar 29, 2013 5:34 PM
      Mark Correct
      Correct Answer
      Thats great.. Looks like what I need, Can you tell me what all changes you made to the model that I have sent??
      
      What's the version you used to simulate it?
      
      Can you send the file please, @vsmokkapati@alaska.edu
      Like • Show 0 Likes0
      Actions
      - Jared Conway @ Vamsi Mokkapati on Mar 29, 2013 5:49 PM
        Mark Correct
        Correct Answer
        I'm running 2013 sp2.0, what version are you running?
        
        I made no changes. Just looked at the setup and ran. Actually I changed from mesh level 8 to 5. Maybe yours completed because of max travels rather than converged goals and that is why your results are wrong. Try level 3 and then 5. Check why completion occurs.
        Like • Show 0 Likes0
        Actions
        Vamsi Mokkapati @ Jared Conway on Mar 29, 2013 6:35 PM
        Mark Correct
        Correct Answer
        I tried this is 2011 and 2012 version, but gives me same higher density values..
        Like • Show 0 Likes0
        Actions
        Jared Conway @ Vamsi Mokkapati on Mar 30, 2013 12:49 PM
        Mark Correct
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        Thats at 25 iterations, have you let it run to completion?
        
        Please setup goals for pressure, temp, density and velocity all all the inlets and outlets, let it run to completion and post.
        Like • Show 0 Likes0
        Actions

Heat Exchanger Simulation with helically corrugated tube.

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