Hi!! please help me my model is rectangular solid with heat flux on the upper face and fluid moving under lower face , I used Conjugate heat transfer ,but the result show that there are no heat transfer between solid and liquid!!
Hey I know this is quite old, but can you explain a bit more about what the intop1(nitf.qwf_u) expression does? Im just not sure how I can apply that to my own model, cheers
John Smith Haha, funny someones asking for this once I look up that video after a few months for my studies at university. I recommend you to not using this expression since it does weird things. Basically it is suppossed to calcualte the heat flux over a defined surface by integrating/accumulating it over the area. In all of my simulations the value of this heat flux is significant different from the analytic calculated value. You will also notice this if you create the heat balance with the calculated temperatures from your model and calculate then the heat flux from it. It will probably differ from the value calculated with nitf.ntflux for laminar or nitf.qwf_u for turbulent flow. I´m not a comsol specialist but I have spend a lot of time with comsol investigating this issue and I´m pretty sure something is wrong with these expressions. I also recommend you to not calculate the heat transfer coefficient with the formular in this video since it is false. You cannot use the inlet temperatures form both flows. You need to use the logarithmica mean temperature difference of the flows (see en.wikipedia.org/wiki/Logarithmic_mean_temperature_difference for easy understanding). Greetings from a german student, currently residing for two months in Florida ;) P.S.: Correct me if I`m talking total bullshit :D
John Smith, Aliengx, here is our answer to your question: The intop1 operator is an integration operator that returns the integral of the expression passed as the argument. The integration is performed over the boundaries separating the two fluids (see intop1 definition in the video at 7:24). The expression, nitf.qwf_u, is a predefined variable that corresponds to the heat flux evaluated on the upside of an internal wall when thermal wall functions are used for turbulent flows. The method shown in this video estimates the overall heat transfer coefficient from the amount of exchanger power divided by the temperature difference. Going into more detail, nitf.qwf_u and nitf.qwf_d are postprocessing variables designed to evaluate heat transfer by conduction through walls where wall functions are used. Since these expressions are not using the spatial gradient of the temperature field to estimate the heat flux, they are more accurate than the gradient based expressions that can be tested manually. An unexpected value of these variable may indicate a non-converged solution or a non-appropriate mesh at the wall (one can check spf.d_w_plus value at walls). Note that on internal walls, ht.ntflux_u and ht.ntflux_d are defined too, and are equal to the sum of nitf.qwf_u (or nitf.qwf_d) + the convective heat flux + the radiative heat flux. Since the wall is immobile and the radiation neglected, we have nitf.qwf_u = ht.ntflux_u. You can find more info on this in the HeatTransferModuleUsersGuide.pdf in the Heat Transfer Module documentation folder. For more specific questions on applying this to your own model, you can email support@comsol.com.
Thanks for this good video. Please, I want the tutorial in detail
This is one pass shell and tube heat exchanger. Can you have the tutorial of 2 pass shell and heat exchanger please upload the video. Thanks
Can you tell how to select Highly conductive walls in Heat transfer as you did , I am using Comsol 5.5
This is beautiful! Thank YOU!
Hello. Are there any ready-made drawings or measurements of the heat exchanger in this video on the internet? Thank you.
any ideas on why Comsol would say intop1(nitf.qwf_u) is undefined variable? im using version 5.0 and replaced air with steam in ur example
Hi!! please help me
my model is rectangular solid with heat flux on the upper face and fluid moving under lower face , I used Conjugate heat transfer
,but the result show that there are no heat transfer between solid and liquid!!
Hey @COMSOL let Me know what is The Final Result Of this Video
Hey I know this is quite old, but can you explain a bit more about what the intop1(nitf.qwf_u) expression does? Im just not sure how I can apply that to my own model, cheers
John Smith Haha, funny someones asking for this once I look up that video after a few months for my studies at university. I recommend you to not using this expression since it does weird things. Basically it is suppossed to calcualte the heat flux over a defined surface by integrating/accumulating it over the area. In all of my simulations the value of this heat flux is significant different from the analytic calculated value. You will also notice this if you create the heat balance with the calculated temperatures from your model and calculate then the heat flux from it. It will probably differ from the value calculated with nitf.ntflux for laminar or nitf.qwf_u for turbulent flow.
I´m not a comsol specialist but I have spend a lot of time with comsol investigating this issue and I´m pretty sure something is wrong with these expressions.
I also recommend you to not calculate the heat transfer coefficient with the formular in this video since it is false. You cannot use the inlet temperatures form both flows. You need to use the logarithmica mean temperature difference of the flows (see en.wikipedia.org/wiki/Logarithmic_mean_temperature_difference for easy understanding).
Greetings from a german student, currently residing for two months in Florida ;)
P.S.: Correct me if I`m talking total bullshit :D
John Smith, Aliengx, here is our answer to your question:
The intop1 operator is an integration operator that returns the integral of the expression passed as the argument. The integration is performed over the boundaries separating the two fluids (see intop1 definition in the video at 7:24). The expression, nitf.qwf_u, is a predefined variable that corresponds to the heat flux evaluated on the upside of an internal wall when thermal wall functions are used for turbulent flows. The method shown in this video estimates the overall heat transfer coefficient from the amount of exchanger power divided by the temperature difference.
Going into more detail, nitf.qwf_u and nitf.qwf_d are postprocessing variables designed to evaluate heat transfer by conduction through walls where wall functions are used. Since these expressions are not using the spatial gradient of the temperature field to estimate the heat flux, they are more accurate than the gradient based expressions that can be tested manually. An unexpected value of these variable may indicate a non-converged solution or a non-appropriate mesh at the wall (one can check spf.d_w_plus value at walls).
Note that on internal walls, ht.ntflux_u and ht.ntflux_d are defined too, and are equal to the sum of nitf.qwf_u (or nitf.qwf_d) + the convective heat flux + the radiative heat flux. Since the wall is immobile and the radiation neglected, we have nitf.qwf_u = ht.ntflux_u.
You can find more info on this in the HeatTransferModuleUsersGuide.pdf in the Heat Transfer Module documentation folder. For more specific questions on applying this to your own model, you can email support@comsol.com.
The,shelldrakejohn
Hi
I want the mph file can anyone send it to me?
me too can you please share the file !!
good morning sir! say me please how to show graphic of the temperature.
thanks