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-   -   automatic way of calculating actual heat transfer coefficient (http://www.cfd-online.com/Forums/cfx/67622-automatic-way-calculating-actual-heat-transfer-coefficient.html)

 Hashmi August 20, 2009 08:38

automatic way of calculating actual heat transfer coefficient

the variable named "Wall heat transfer coefficient" uses near wall temperature which is not the bulk temperature of the fluid.
In a wall bounded flow is there a way to calculate the correct local bulk temperature automatically as well as the local wall heat transfer coefficient?

(setting tbulk for htc dont work for local bulk temperature)

Hashmi

 ghorrocks August 20, 2009 18:44

By default it calculates a local bulk temperature and wall HTC. You can activate an expert parameter to define a fixed bulk temperature if you like.

Also bear in mind that the HTC returned by the solver is calculated from the wall heat transfer. That means from the wall heat transfer variable if you don't like the bulk temperature it used you can recalculate it based on whatever bulk temperature you like.

 Hashmi August 23, 2009 09:00

automatic way of calculating actual heat transfer coefficient

Thanks Glenn Horrocks for the reply.I know wall heat transfer is a local variable, but in wall bounded flows the bulK temperature is also a variable, I mean in the pipe flow it changes along the length of the pipe, So for calculating actual local heat transfer the fixed value of bulk temperature is of no use.

In simple geometries like pipe, one can do it manually in excel by exporting velocity and temperature field but for complex geometries this is a cumbersome process, and there are not much nodes as well in complex geometries at one cross section along the flow.

I am interested in some automatic way of calculating the actual heat transfer which is based on local bulk temperature.

Hashmi

 ghorrocks August 23, 2009 18:36

There is no universal way of doing this. In fact as soon as you start using an arbitrary definition for the bulk temperature then there is little point in using convection coefficients and you should consider looking at the heat transfer calculated directly - which is how CFX calculates the wall heat transfer in the first place.

So I doubt you are heading in a useful direction by attempting to do a better definition of the bulk temperature.

 Goutam July 26, 2012 06:54

Quote:
 Originally Posted by Hashmi (Post 227218) Thanks Glenn Horrocks for the reply.I know wall heat transfer is a local variable, but in wall bounded flows the bulK temperature is also a variable, I mean in the pipe flow it changes along the length of the pipe, So for calculating actual local heat transfer the fixed value of bulk temperature is of no use. In simple geometries like pipe, one can do it manually in excel by exporting velocity and temperature field but for complex geometries this is a cumbersome process, and there are not much nodes as well in complex geometries at one cross section along the flow. I am interested in some automatic way of calculating the actual heat transfer which is based on local bulk temperature. Hashmi
Dear Hashmi,
I am considering a pipe flow simulation. L=1.2m, R=0.05m, Re=300, Umean=0.047157m/s at T=300K.Parabolic velocity profile at the inlet, no-slip Bcs at the wall. Inlet T=300K, wall T=315 K. I have calculated U and T and it gives me the correct results but Nu is 2.5 (Actual value is 3.66). COuld you please help me. How I will do this manually in excel?

Thanks for your time and cooperation.

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