Why Does Reynolds Analogy Overestimate Heat Transfer?

AI Thread Summary
Reynolds Analogy and other empirical correlations tend to overestimate heat transfer in turbulent pipe flow, as observed in recent experiments. The predictions using both simple and modified Reynolds Analogy, along with the Dittus-Boetler correlation, consistently resulted in higher Nusselt numbers than measured. Potential reasons for this discrepancy include unaccounted energy losses, possibly due to lagging materials around the pipe. The analogy is primarily applicable to gases, and its assumptions may not hold true in the presence of profile drag or for liquids. Understanding these limitations is crucial for accurate heat transfer predictions.
hanson
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Hi all.
Why Reynolds Analogy and other empirical relations always overesimate heat transfer?
I have done an experiment on turbulent pipe flow (smooth pipe) and I used Reynold Analogy (both the simple (Pr=1) and the modified one) and the Dittus-Boetler correlation equation to do the predictions.
It turns out that all those predictions over-estimate the heat transfer i.e. the Nusselt number at each Reynolds number.
I can't figure out why...
Is that there are some kind of energy or heat loss not considered? (There is some lagging material around the pipe and the loss through the laggin materials has been measured)

Please share your views. Thanks.
 
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As far as I know the analogy is best used for gases. If there is profile drag or a liquid, the assumption cannot be used. Again, it's been a while so I could be wrong.
 
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