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Surface temperature dependent heat transfer coefficient

Posted 24.03.2013, 12:42 GMT-4 Heat Transfer & Phase Change Version 4.3 4 Replies

Kaushik Biswas
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I'd like to apply a convection heat transfer boundary condition to the attached problem. Currently I am using a constant convection coefficient (h=10 W/m2K) on the interior gypsum surface. I have defined the room interior temperature using an interpolation function (Troom). I'd like to insert an analytical function for 'h', of the form '(Troom - T_surface)/Length'. 'T-surface' is, of course, being calculated by the solver. I added a point probe (Ts_Gyp) under 'Definitions', but not sure how to insert a function relating 'h' to 'T_surface (Ts_Gyp)'. Any suggestions?

I'd appreciate the help.

Regards,
Kaushik

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4 Replies Last Post 18.11.2014, 05:56 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 24.03.2013, 14:57 GMT-4
Hi

but that is what the convective BC is doing anyhow, If you put 293[K] in the reference temperature it is a scalar, constant value, but if you have efined a field my_T(x,y,z) and use your my_T in the reference temperature entry, and your BC defines a maping to a given (x,y,z) then you are changing the reference temeperautre depending on your (x,y,z,t) location (t is option as you might not be solving for t

This is COMSOL's "implicit" notation, it's often confusing, but any scalar entry in a BC field, can also be a field depending on the (x,y,z) (and t) of the BC area

--
Good luck
Ivar
Hi but that is what the convective BC is doing anyhow, If you put 293[K] in the reference temperature it is a scalar, constant value, but if you have efined a field my_T(x,y,z) and use your my_T in the reference temperature entry, and your BC defines a maping to a given (x,y,z) then you are changing the reference temeperautre depending on your (x,y,z,t) location (t is option as you might not be solving for t This is COMSOL's "implicit" notation, it's often confusing, but any scalar entry in a BC field, can also be a field depending on the (x,y,z) (and t) of the BC area -- Good luck Ivar
Kaushik Biswas
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Posted: 1 decade ago 26.03.2013, 11:35 GMT-4
Ivar,

Thanks for the response. I think I understand what you're saying as, the 'T' in the BC equation 'qo=h.(Text-T)' is automatically the surface temperatrue computed by COMSOL. However, the convection coefficient 'h' is currently a constant. If I want to make it a function of the surface and room temperatures, or h=h(Text,T), how do I do that? First, I need to define a surface temperature, correct? I am trying to do so by adding a surface probe. Is that the way to do it, or is there an easier way?

Thanks again.
Kaushik
Ivar, Thanks for the response. I think I understand what you're saying as, the 'T' in the BC equation 'qo=h.(Text-T)' is automatically the surface temperatrue computed by COMSOL. However, the convection coefficient 'h' is currently a constant. If I want to make it a function of the surface and room temperatures, or h=h(Text,T), how do I do that? First, I need to define a surface temperature, correct? I am trying to do so by adding a surface probe. Is that the way to do it, or is there an easier way? Thanks again. Kaushik
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 26.03.2013, 13:11 GMT-4
Hi

but you can replace "h" by a function or an equation of your own see example 4.3a below


--
Good luck
Ivar
Hi but you can replace "h" by a function or an equation of your own see example 4.3a below -- Good luck Ivar
Sefik Behrem
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Posted: 1 decade ago 18.11.2014, 05:56 GMT-5
Hello Ivar,
If the heat transfer coefficient h = f (t, z) boundary condition, and T = f (t), in order to extract the h = f (T, z)?
  T is the surface temperature.
Thank you!
Hello Ivar, If the heat transfer coefficient h = f (t, z) boundary condition, and T = f (t), in order to extract the h = f (T, z)?   T is the surface temperature. Thank you!

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