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-   -   Heat transfer coefficient - what is waht (https://www.cfd-online.com/Forums/fluent/40570-heat-transfer-coefficient-what-waht.html)

macfly March 11, 2014 10:42
Quote:
Originally Posted by FLUENT CFD (Post 479365)
Hi

What do you mean the Bulk Temp.?? is it inlet fluid temp??

thanks
http://lmgtfy.com/?q=fluid+bulk+temperature

;)

Shreman July 10, 2017 12:08
Quote:
Originally Posted by cdf_user (Post 302672)
The h values reported by the fluent are wrong. It has something to do with the reference temperature which can be different for different models. Ask fluent engineer. To get the right h value you need to write a udf.

h = heat_flux / (T(z) - Tbulk(z))

Tbulk = SUM mu*cp*rho*Tf dA / SUM mu*cp*dA
Could you tell me where did you get this formula from because for the Tbulk dimesions donīt match on both side..

Rajaero August 14, 2017 04:09
hello guys,
i am also doing the forced convection problem between the solid body and fluid domain. i have read all of your comments and i followed all of it. so my question is that after i changes the reference temperature in fluent i got some h value. but i wanna make sure whether that h value is correct or not.

if somebody explain, how to write a UDF for calculating the exact h value.

Thanks in advance.

sb16 August 20, 2018 06:41
about udf.
 
Quote:
Originally Posted by cdf_user (Post 302672)
The h values reported by the fluent are wrong. It has something to do with the reference temperature which can be different for different models. Ask fluent engineer. To get the right h value you need to write a udf.

h = heat_flux / (T(z) - Tbulk(z))

Tbulk = SUM mu*cp*rho*Tf dA / SUM mu*cp*dA



can you please elaborate on how and where to write udf.?

Sai Krishna August 31, 2020 06:41
Quote:
Originally Posted by FLUENT CFD (Post 479365)
Hi

What do you mean the Bulk Temp.?? is it inlet fluid temp??


thanks
no its the average temperature of inlet and outlet for an internal flow. its not physically correct to take one temperature (inlet) to estimate the fluid properties, as fluid temperature is continuously changing from inlet to outlet because of heat transfer. hence,if u want to calculate what would be the heat transfer and coefficients usually we will take average of inlet and outlet temperatures.

Regards

somia baali December 21, 2021 06:14
Quote:
Originally Posted by Chandra Murthy
;131254
Fluent directly calculates heat flux on the boundaries. In Fluent, heat transfer coefficient (h) is a derived quantity using reference temperature, adjacent fluid temperature and heat flux. In the actual scenario, the reference temperature should be the wall temperature. Therefore, the values reported by fluent will be an indicative values. To get the actual h values you need to write a UDF according to your need.
what is wall temperature? and how can i determined?please

LuckyTran December 21, 2021 13:43
This entire thread is whack.

The bulk temperature is the mixed temperature at each location. It is not the average of the inlet and outlet. It is the temperature the flow would have if you magically somehow mixed all of it together. The inlet has an inlet bulk temperature. The outlet has an outlet bulk temperature. Everywhere, has a bulk temperature.

For internal heat transfer, the bulk temperature is commonly used as the reference temperature for the heat transfer coefficient but also for all the fluid properties. Some people are too lazy, or they just don't have the skill to calculate the bulk temperature and they will use the average of the inlet and outlet instead as a very crude approximation.

The wall temperature should not be used for the reference temperature, that would just make the heat transfer coefficient undefined because htc=q"/0.

Wall temperature you get from Fluent.

somia baali December 29, 2021 07:13
thank you a lot about the answer, but how can i found wall temperature from fluent

LuckyTran December 29, 2021 16:29
There is a variable literally labeled wall temperature in Fluent. Just plot it.


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