Why Does Reynolds Analogy Overestimate Heat Transfer?

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SUMMARY

The discussion centers on the overestimation of heat transfer predictions using Reynolds Analogy and the Dittus-Boetler correlation in turbulent pipe flow experiments. The user observed that both the simple and modified Reynolds Analogy, as well as the Dittus-Boetler equation, consistently overestimated the Nusselt number across various Reynolds numbers. The user speculates that unaccounted energy or heat losses, particularly through lagging materials around the pipe, may contribute to this discrepancy. It is noted that Reynolds Analogy is primarily applicable to gases, and its assumptions may not hold for liquids or scenarios involving profile drag.

PREREQUISITES
  • Understanding of turbulent flow dynamics
  • Familiarity with Nusselt number and heat transfer coefficients
  • Knowledge of Reynolds Analogy and its applications
  • Experience with the Dittus-Boetler correlation for heat transfer predictions
NEXT STEPS
  • Investigate the limitations of Reynolds Analogy in liquid flow scenarios
  • Explore alternative empirical correlations for heat transfer in turbulent flow
  • Examine methods to quantify heat loss through insulation materials
  • Learn about the impact of profile drag on heat transfer efficiency
USEFUL FOR

Mechanical engineers, thermal system designers, researchers in fluid dynamics, and anyone involved in heat transfer analysis in piping systems.

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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