Why Does Reynolds Analogy Overestimate Heat Transfer?

In summary, the conversation discusses the overestimation of heat transfer by Reynolds Analogy and other empirical relations in an experiment on turbulent pipe flow. The individual conducting the experiment has found that these predictions overestimate the heat transfer, but is unsure of the reason why. They ask for others' views and suggest that the analogy may not be applicable for liquids or in cases of profile drag.
  • #1
hanson
319
0
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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  • #2
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.
 

FAQ: Why Does Reynolds Analogy Overestimate Heat Transfer?

Why is Reynolds Analogy used to estimate heat transfer?

Reynolds Analogy is used to estimate heat transfer because it provides a simple and convenient way to relate the heat transfer coefficient and the skin friction coefficient. This allows for a more efficient estimation of heat transfer in situations where the flow is turbulent, which is often the case in engineering applications.

How does Reynolds Analogy overestimate heat transfer?

Reynolds Analogy is based on the assumption that the turbulent momentum and heat transfer processes are similar. However, in reality, the transport of heat and momentum are not always directly proportional. Therefore, in some situations, the analogy can lead to an overestimation of heat transfer.

What factors contribute to the overestimation of heat transfer by Reynolds Analogy?

There are several factors that can contribute to the overestimation of heat transfer by Reynolds Analogy. These include the presence of heat sources or sinks in the flow, variations in temperature across the boundary layer, and the effect of turbulence on the heat transfer process.

Can the overestimation of heat transfer by Reynolds Analogy be corrected?

Yes, the overestimation of heat transfer by Reynolds Analogy can be corrected by using correction factors or by modifying the analogy to account for the specific conditions of the flow. Additionally, more accurate results can be obtained by using experimental data or more advanced computational methods.

Are there any situations where Reynolds Analogy does not overestimate heat transfer?

Yes, there are situations where Reynolds Analogy does not overestimate heat transfer. For example, in fully developed turbulent flow, where the flow is fully developed and the temperature profile is not changing, the analogy can provide accurate results. However, in most cases, the analogy will need to be modified or corrected to account for the overestimation of heat transfer.

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