Shell and tube heat exchanger, correlation

[PaulLag]

Hi there

hope you are fine.
please, I am contacting you for following topic.

Please, I would like to know if someone can suggest me a correlation for a following case
- shall and tube heat exchanger
- finned tube
- water as external medium.

I'd like to calculate the external heat transfer coefficient.

I assume it would be a correlation including a Reynolds number.
In this case, it would be interesting to know which is the dimensional characteristic considered in this number

Would it be possible to know any value, as indicative, in order to have a rule of thumb ?

I have really digged into the web, but I have not been able to find any clear answer

Thanks !

 

[willard3]

Just to start, go back to your heat transfer textbook. Read about LMTD.

 

[PaulLag]

Hello

thanks for your answer.
I apologize for not being clear enough, so that I will try to explain me better.
Indeed my question was not concerning LMTD, but

Q = UA*LMTD

Q is the heat exchanger capacity
A is the reference area
LMTD is logatitmic mean temperature

Specifically

U = 1/h_ext + 1/hint(d_ext/d_int)+(d_ext/2)*ln(d_ext/d_int)/Tube_conductivity

where
h is the heat transfer coefficient (ext stands for external, int for internal)
d is the tube diameter

said this, I'd kindly need a correlation for h_ext.

Thanks in advance for your help !

 

[georgeverghese]

From memory, the chapter Extended Surfaces in "Process Heat Transfer" by DQ Kern has the necessary guidance on this and dp calcs for finned HX design.