Is there any writeup on how this feature works or is supposed to be used? The section 2.2.5 of the 'Equipment and Utilities Guide' seems to have nothing about this feature.
Where is the estimated HTC reported?
Last edit: JMB 2016-01-06
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The procedure is the same as the one found in heat exchange books, the inverse of the overall coefficient is equal to the sum of the inverse of the individual contributions of the external environment, pipe wall, insulation (if any) and the internal fluid itself
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Ok. I quickly read the code and see the method, which is as you described, a classical summation of inverse contributions that results in CALCULAR_CGTC being calculated. If it is C#, I could get the gist of it. I am not a C# coder.
Where in the nice GUI screeen / interface (of DWSIM) does this value get displayed for the end user? How is the calculation initiated by a user? After one fills out the proper values in the pop-up window, how does one tell it to compute CALCULAR_CGTC?
Can you elaborate some more please?
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Would you help us understand how one can use the 'Estimate Overall HTC' feature please? Is it available as a viewable value, an internal variable that can be used in a user script, or something else? Thanks.
Regards, JMB
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I am still clueless as what I am supposed to do after filling out this section.
After I close this pop-up window and click on 'Re-calculate' all I see no change in the Energy stream. It is still zero. There is no change to the outlet fluid temperature (it remains at 298.157K. Am I not seeing something that is supposed to be there?
I will try to attach a simplified simulation to this forum, since what I am working on is company proprietary. Hope you can find the time to look into it and provide guidance.
What is the length of your pipe segment? The calculated overall HTC will be displayed in the results graph. It is used internally by DWSIM to calculate heat exhanged between the fluid and the surroundings through the pipe wall.
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Actually I am using _b5849. I also captured a mono-debug.log which I have attached. It is too complex/long for me to diagnose what could be causing the problem.
I tried playing around with various values in the attached simulation, but found that DWSIM estimates very low values (several orders of magnitude less) for the Overall HTC as compared to the reference above. What am I doing wrong?
I finally figured out where to look for the 'Overall HTC' output!
PIPE-OOO - View Results (Chart): 0.045 (W/[m2.K])
EngrToolBox: 11.3 (W/[m2.K])
I have not calculated NRe in the PIPE-000 yet. BTW is there a way to display NRe in a Master Table or UO Table if I write a script for it? I think the ability to readily see the usual gamut of dimensionless numbers pertinent to a certain stream/UO would be a terrific feature! Hint, Hint !
There was a problem with thermal conductivity and heat capacity units.
Once you have the results of the pipe calculation, it is very very easy to calculate U, you can use the spreadsheet for that and display a Linked Spreadsheet Table in the flowsheet.. remember that Q = UxAxDT... :)
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Hello Daniel, I have tested :
_v36_b5851_beta.zip" # Build [git-5a66f7c] (08/01/2016)
and suspect that the HTC calculation for insulation may have a problem. Here is why. In a simulation involving 1,2-propanediol+Water (DWSIM db w/ NRTL) the calculation using: [v] Include pipe walls [v ] Include internal HTC [ ] Incluce Insulation [v] Include external HTC
I do see a reasonable and corresponding change in temperature & the energy stream seems plausible and non zero. This build fixed the previously discovered 0 energy, incorrect U calc problem.
However if I add 125 mm of Polyurethane insulation: [v] Include pipe walls [v ] Include internal HTC [v] Incluce Insulation [v] Include external HTC
I see no change to the temperature difference and no change in the energy from the previous scenario, which is not normal. I cannot attach the simulation because it is proprietary.
Would you kindly verify if there is a bug using the Est_HTC_Bug2.dwxml file I attached in the other posting of this forum? Thank you.
One more possible clue I can offer is that after I saved the simulation, closed DWSIM and restarted it and recalculated it, now there is a drop in the energy stream although not as much as I would expect (as I have added as much as 125mm of polyurethane insulation).
Possibility: Is the insulation thickness not being "registered" somewhere in RAM, but it is getting saved to the file, to be correctly read in when DWSIM is restarted?
Last edit: JMB 2016-01-11
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Try build 5854, it may include a fix to this problem, although I wasn't able to reproduce it. It also includes two new calculation modes for the Pipe UO and I've added more information about the U calculation procedures in the F1 help section.
The results table also includes all calculated Us if you selected the overall U calculation option.
Regards
Daniel
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Just a minor change to the 'Properties Section, where we have:
4. Miscellanea
4. Results
the latter can be changed to '5. Results'. I say this is very minor.
I am thrilled that the calculation works now for UA estimation with and without the insulation too. I can see the difference in the energy stream when the insulation is switched off. Brilliant!
DWSIM 3.6 Build 5859 [git-9b6a447] (16/01/2016)
Mono JIT compiler version 4.2.1 (Stable 4.2.1.102/6dd2d0d Thu Nov 12 09:52:44 UTC 2015)
Ubuntu 12.04.5 LTS 64 bit
Last edit: JMB 2016-01-16
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Hi Daniel, I've just downloaded and installed the latest version of DWSIM and in my case it still does not seem to work correctly. I've attached a screenshot of the pipe segment details. I'm trying to estimate the HTC (but not use the external insulation). I've did the same calculation in Promax and I'm getting around 5kW of heat loss. Water temperature is at 20ºC and external temperature is -20ºC with 10m/s wind speed. A 4m long pipe of 650mm diameter.
Hi again, I think I've found the problem. As you can see in the image of the previous post, I had selected the material "Steel" (since I'm simulating it for a stainless steel pipe). In the results the k value of the steel wall is 0 W/m2K, which is hard to believe (see image). I tried it again but this time with Carbon steel as material and now I do get more coherent values as result.
So maybe a sugestion for the next update; add stainless steel to the library of possible materials for the pipe segment with a completed library?
Yes, you've found the problem but there was another one even worse. No matter which material you choose, the temperature sent to the conductivity calculator was always zero. "Steel" is in fact Stainless Steel, it was lost in translation... the k = f(T) function for it was wrong too, returning absurdly high values.
Everything in the above was fixed and now I've got expected results. I'll release a new version on the weekend.
Is there any writeup on how this feature works or is supposed to be used? The section 2.2.5 of the 'Equipment and Utilities Guide' seems to have nothing about this feature.
Where is the estimated HTC reported?
Last edit: JMB 2016-01-06
No, it doesn't, but you can take a look at the actual calculation function on https://github.com/DanWBR/dwsim3/blob/master/DWSIM/Objects/UnitOps/Pipe.vb, line 1099.
The procedure is the same as the one found in heat exchange books, the inverse of the overall coefficient is equal to the sum of the inverse of the individual contributions of the external environment, pipe wall, insulation (if any) and the internal fluid itself
Ok. I quickly read the code and see the method, which is as you described, a classical summation of inverse contributions that results in CALCULAR_CGTC being calculated. If it is C#, I could get the gist of it. I am not a C# coder.
Where in the nice GUI screeen / interface (of DWSIM) does this value get displayed for the end user? How is the calculation initiated by a user? After one fills out the proper values in the pop-up window, how does one tell it to compute CALCULAR_CGTC?
Can you elaborate some more please?
Hello Daniel,
Would you help us understand how one can use the 'Estimate Overall HTC' feature please? Is it available as a viewable value, an internal variable that can be used in a user script, or something else? Thanks.
Regards, JMB
Open the Pipe's thermal profile editor and you'll see.
I am still clueless as what I am supposed to do after filling out this section.
After I close this pop-up window and click on 'Re-calculate' all I see no change in the Energy stream. It is still zero. There is no change to the outlet fluid temperature (it remains at 298.157K. Am I not seeing something that is supposed to be there?
I will try to attach a simplified simulation to this forum, since what I am working on is company proprietary. Hope you can find the time to look into it and provide guidance.
What is the length of your pipe segment? The calculated overall HTC will be displayed in the results graph. It is used internally by DWSIM to calculate heat exhanged between the fluid and the surroundings through the pipe wall.
I have tried 1m, 100m, Carbon Steel, PVC, etc
Still using the old version? The new one fixes this error in section X bug.
Actually I am using _b5849. I also captured a mono-debug.log which I have attached. It is too complex/long for me to diagnose what could be causing the problem.
Last edit: JMB 2016-01-08
Use this build from yesterday http://sourceforge.net/projects/dwsim/files/DWSIM/DWSIM%203.6/dwsim_3.6.5850.37060-beta.deb/download
Last edit: Daniel Medeiros 2016-01-08
Do you have a _b5850 zip build instead of the deb? I am not ready to install a deb package yet.
I have a fresh build, 7zip-compressed. http://sourceforge.net/projects/dwsim/files/DWSIM/DWSIM%203.6/DWSIM_bin_v36_b5851_beta.7z/download
Fabulous!
Hello Daniel,
I am trying out the Estimate Overall HTC part of a pipe Segment. I am using this as a rough guide:
http://www.engineeringtoolbox.com/overall-heat-transfer-coefficients-d_284.html
I tried playing around with various values in the attached simulation, but found that DWSIM estimates very low values (several orders of magnitude less) for the Overall HTC as compared to the reference above. What am I doing wrong?
I finally figured out where to look for the 'Overall HTC' output!
PIPE-OOO - View Results (Chart): 0.045 (W/[m2.K])
EngrToolBox: 11.3 (W/[m2.K])
I have not calculated NRe in the PIPE-000 yet. BTW is there a way to display NRe in a Master Table or UO Table if I write a script for it? I think the ability to readily see the usual gamut of dimensionless numbers pertinent to a certain stream/UO would be a terrific feature! Hint, Hint !
I've fixed U calculation in https://github.com/DanWBR/dwsim3/commit/10e3a83980c49e7b557e6f7c764a6b9b690bb4c2
There was a problem with thermal conductivity and heat capacity units.
Once you have the results of the pipe calculation, it is very very easy to calculate U, you can use the spreadsheet for that and display a Linked Spreadsheet Table in the flowsheet.. remember that Q = UxAxDT... :)
I'll upload a new build with this fix in a few minutes.
Back to the ZIP file format: http://sourceforge.net/projects/dwsim/files/DWSIM/DWSIM%203.6/DWSIM_bin_v36_b5851_beta.zip/download
Hello Daniel, I have tested :
_v36_b5851_beta.zip" # Build [git-5a66f7c] (08/01/2016)
and suspect that the HTC calculation for insulation may have a problem. Here is why. In a simulation involving 1,2-propanediol+Water (DWSIM db w/ NRTL) the calculation using:
[v] Include pipe walls
[v ] Include internal HTC
[ ] Incluce Insulation
[v] Include external HTC
I do see a reasonable and corresponding change in temperature & the energy stream seems plausible and non zero. This build fixed the previously discovered 0 energy, incorrect U calc problem.
However if I add 125 mm of Polyurethane insulation:
[v] Include pipe walls
[v ] Include internal HTC
[v] Incluce Insulation
[v] Include external HTC
I see no change to the temperature difference and no change in the energy from the previous scenario, which is not normal. I cannot attach the simulation because it is proprietary.
Would you kindly verify if there is a bug using the Est_HTC_Bug2.dwxml file I attached in the other posting of this forum? Thank you.
Regards, JMB
See: https://sourceforge.net/p/dwsim/discussion/844529/thread/0be1a0e3/
Last edit: JMB 2016-01-11
One more possible clue I can offer is that after I saved the simulation, closed DWSIM and restarted it and recalculated it, now there is a drop in the energy stream although not as much as I would expect (as I have added as much as 125mm of polyurethane insulation).
Possibility: Is the insulation thickness not being "registered" somewhere in RAM, but it is getting saved to the file, to be correctly read in when DWSIM is restarted?
Last edit: JMB 2016-01-11
Try build 5854, it may include a fix to this problem, although I wasn't able to reproduce it. It also includes two new calculation modes for the Pipe UO and I've added more information about the U calculation procedures in the F1 help section.
The results table also includes all calculated Us if you selected the overall U calculation option.
Regards
Daniel
Excellent !!! I will try it out soon...
And yes it works well now! Thank you... :)
Just a minor change to the 'Properties Section, where we have:
4. Miscellanea
4. Results
the latter can be changed to '5. Results'. I say this is very minor.
I am thrilled that the calculation works now for UA estimation with and without the insulation too. I can see the difference in the energy stream when the insulation is switched off. Brilliant!
DWSIM 3.6 Build 5859 [git-9b6a447] (16/01/2016)
Mono JIT compiler version 4.2.1 (Stable 4.2.1.102/6dd2d0d Thu Nov 12 09:52:44 UTC 2015)
Ubuntu 12.04.5 LTS 64 bit
Last edit: JMB 2016-01-16
Hi Daniel, I've just downloaded and installed the latest version of DWSIM and in my case it still does not seem to work correctly. I've attached a screenshot of the pipe segment details. I'm trying to estimate the HTC (but not use the external insulation). I've did the same calculation in Promax and I'm getting around 5kW of heat loss. Water temperature is at 20ºC and external temperature is -20ºC with 10m/s wind speed. A 4m long pipe of 650mm diameter.
Any sugestions what it could be?
Regards,
GSalomons
Hi again, I think I've found the problem. As you can see in the image of the previous post, I had selected the material "Steel" (since I'm simulating it for a stainless steel pipe). In the results the k value of the steel wall is 0 W/m2K, which is hard to believe (see image). I tried it again but this time with Carbon steel as material and now I do get more coherent values as result.
So maybe a sugestion for the next update; add stainless steel to the library of possible materials for the pipe segment with a completed library?
Regards,
GSalomons
Hi GSalomons,
Yes, you've found the problem but there was another one even worse. No matter which material you choose, the temperature sent to the conductivity calculator was always zero. "Steel" is in fact Stainless Steel, it was lost in translation... the k = f(T) function for it was wrong too, returning absurdly high values.
Everything in the above was fixed and now I've got expected results. I'll release a new version on the weekend.
Thanks.
Daniel