Talk:Heat transfer coefficient

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How can Q be a power input? Isn't power \dot{Q}, J/s?

answer: right. Q is the heat, P is the power
\dot{Q} = \frac{dQ}{dt} = P
[Q]=J and [P]=W=J/s


obviosly Q=h \cdot A \cdot \Delta T is wrong
correct would be: Q=h \cdot A \cdot \Delta T \cdot \Delta t to check this, you can simply put in the units: Q is in J; h is in W / (m² * K) where W=J/s; delta T is in K and delta t is in s. so:
J = \frac{W}{m^2 \cdot K} \cdot m^2 \cdot K
J = W = J / s is wrong. when you multiply it by s you get J = (J/s) * s = J which is right.

Please!!! Someone help improve this. This topic deserves pages and pages, with links to all the different correlations and when they are applicable.

I don't think this is really what is needed. There are literally thousands of heat transfer correlations - perhaps this article could refer the reader to the "Handbook of Heat Transfer" by McGraw-Hill. What is needed is a much better explanation of the Heat Transfer Coefficient. Using internal flow as an example is a really bad idea, since it should include a correct treatment of log-mean temperature difference. External flow is much simpler, and would get the general concept across better -- which is a better objective, I think. If someone improves this, that's what I'd recommend. (BTW, the Dittus Boelter is kinda out of date anyway. There are now much better correlations for fully developed pipe flow. Dr. David Naylor

[edit] LMTD

Please Help.

how can i measure the efficiency regarding heat input and output in shell and tube heat exchanger?

[edit] Properties table removed

I removed some text from the article. It was a table of Prandtl number and thermal conductivity of air. Not really relevant to the article. My reasoning is this, Prandtl number has its own article, and equating thermal conductivity and heat transfer coefficient is just plain wrong. Especially for air.Djd sd (talk) 05:12, 30 January 2008 (UTC)