HTC: How to choose reference temperature value

halcyon · February 27, 2012, 08:26

Hi,
I am doing a simulation (laminar,steady) to predict the HTC between a solid body (23°C) and air (20°C).
I thought that the temperature reference value you can choose in the HTC field function should be somehow related to the air temperature in my case.
But if I choose the T_ref 20°C I get an HTC interval of [-1.5,18]. If I choose T_ref 18°C the HTC look much better within an interval of [-0.5,5].

Is there any rule how to choose this value and is it OK to use that value that makes the simulation more realistic?
For me such a "playing around" method doesn't seem to be very professional...

misagh · April 12, 2012, 07:07

i have the same problem.
i dont know which tem. to choose for ref. value.
a tube entering water @300 exiting @302
it is so sensitive to tempreture value.
any help is appreciated.

RobertB · April 12, 2012, 09:19

Typically HTCs are referred to the bulk entrance gas temperature, as it is easy to measure experimentally.

If you have very low T rises then it is not surprising that your HTC will move around significantly as the dT is very small.

You will need to use variable fluid properties and an appropriate grid. You also need to make sure that your model is set up exactly the same as the experiment it is trying to reproduce.

misagh · April 12, 2012, 12:46

yes.you are right.when i choose enterace tempreture the diagrams trend is like that of the experimental diagram,but with significant error./exp. digram is available/
thats because of mesh unaccuracy.
any way,thank you Robert.

February 27, 2012, 08:26	HTC: How to choose reference temperature value	#1
halcyon New Member Join Date: Jan 2012 Posts: 1 Rep Power: 0	Hi, I am doing a simulation (laminar,steady) to predict the HTC between a solid body (23°C) and air (20°C). I thought that the temperature reference value you can choose in the HTC field function should be somehow related to the air temperature in my case. But if I choose the T_ref 20°C I get an HTC interval of [-1.5,18]. If I choose T_ref 18°C the HTC look much better within an interval of [-0.5,5]. Is there any rule how to choose this value and is it OK to use that value that makes the simulation more realistic? For me such a "playing around" method doesn't seem to be very professional... Last edited by halcyon; February 27, 2012 at 09:34.

April 12, 2012, 07:07	reference value	#2
misagh Member misagh Join Date: Apr 2012 Posts: 64 Rep Power: 14	i have the same problem. i dont know which tem. to choose for ref. value. a tube entering water @300 exiting @302 it is so sensitive to tempreture value. any help is appreciated.

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April 12, 2012, 09:19		#3
RobertB Senior Member Robert Join Date: Jun 2010 Posts: 117 Rep Power: 17	Typically HTCs are referred to the bulk entrance gas temperature, as it is easy to measure experimentally. If you have very low T rises then it is not surprising that your HTC will move around significantly as the dT is very small. You will need to use variable fluid properties and an appropriate grid. You also need to make sure that your model is set up exactly the same as the experiment it is trying to reproduce.

April 12, 2012, 12:46		#4
misagh Member misagh Join Date: Apr 2012 Posts: 64 Rep Power: 14	yes.you are right.when i choose enterace tempreture the diagrams trend is like that of the experimental diagram,but with significant error./exp. digram is available/ thats because of mesh unaccuracy. any way,thank you Robert.