Does the heat transfer coefficient changes with system pressure?

h0rst · June 12, 2017, 01:50

Hello everybody,

I was in discussion with some people about the influence on system pressure on the heat transfer coefficient. Some say that pressure has an influence on the boundary layer and therefore also on the heat transfer coefficient.

Is that true and is there a relation?

When calculating heat transfer coefficients, I usually choose the Gnielinski equation with Konkanov coefficient but I do not see where to adapt the pressure there.

Best regards
h0rst

jbreunig · June 12, 2017, 09:36

Conceptually, I could see how pressure could effect heat transfer. Higher pressure means molecules are closer together, which could change heat transfer rate. So really, density is the effect. I don't have my book in front of me right now, but I imagine density should come into play since it's in Reynolds and Prandtl numbers.

h0rst · June 13, 2017, 01:51

Thank you for the answer.

I would also think that the higher pressure has an influence only on the density, so if we use an incompressible fluid like water, this influence would be very small and hardly measurable when we are in a range of approximately 1-10 bar.

Best regards
h0rst

jbreunig · June 13, 2017, 08:15

No problem. I would agree that pressure would not have an effect with water in the pressure ranges that you're dealing with.

June 12, 2017, 01:50	Does the heat transfer coefficient changes with system pressure?	#1
h0rst Member Join Date: Nov 2016 Posts: 73 Rep Power: 9	Hello everybody, I was in discussion with some people about the influence on system pressure on the heat transfer coefficient. Some say that pressure has an influence on the boundary layer and therefore also on the heat transfer coefficient. Is that true and is there a relation? When calculating heat transfer coefficients, I usually choose the Gnielinski equation with Konkanov coefficient but I do not see where to adapt the pressure there. Best regards h0rst

June 12, 2017, 09:36		#2
jbreunig New Member Jim Breunig Join Date: Jun 2017 Posts: 12 Rep Power: 8	Conceptually, I could see how pressure could effect heat transfer. Higher pressure means molecules are closer together, which could change heat transfer rate. So really, density is the effect. I don't have my book in front of me right now, but I imagine density should come into play since it's in Reynolds and Prandtl numbers. __________________ CFD Consulting FEA Consulting

June 13, 2017, 08:15		#4
jbreunig New Member Jim Breunig Join Date: Jun 2017 Posts: 12 Rep Power: 8	No problem. I would agree that pressure would not have an effect with water in the pressure ranges that you're dealing with. __________________ CFD Consulting FEA Consulting

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June 13, 2017, 01:51		#3
h0rst Member Join Date: Nov 2016 Posts: 73 Rep Power: 9	Thank you for the answer. I would also think that the higher pressure has an influence only on the density, so if we use an incompressible fluid like water, this influence would be very small and hardly measurable when we are in a range of approximately 1-10 bar. Best regards h0rst