Heat Transfer Coefficients: Free and Forced Convection

[Monochromoton]

Hi all. I'm currently working on a problem where I have to determine individual and overall heat transfer coefficients for a vertical cylinder with water flowing on the inside and steam on the outside (parallel flow), studying the cases of free and forced convection. I only have four temperatures to work with (both inlets and outlets) and the steam pressure. I am using Nusselt correlations but I am very confused as to whether I am to determine a single heat transfer coefficient using the mean of the steam and water temperatures respectively or if by individual coefficients it refers to one at the inlet and one at the outlet and from those two determine an overall coefficient. Instructions say to use the film temperature which I've been taking as the average between the means since I have nothing else to work with, hence my doubt of whether I can obtain an individual coefficient for the inlet and one for the outlet or if that's a mistake. Any help would be greatly appreciated. If any more information is required please let me know. Thank you.

 

[Chestermiller]

Hi all. I'm currently working on a problem where I have to determine individual and overall heat transfer coefficients for a vertical cylinder with water flowing on the inside and steam on the outside (parallel flow), studying the cases of free and forced convection. I only have four temperatures to work with (both inlets and outlets) and the steam pressure. I am using Nusselt correlations but I am very confused as to whether I am to determine a single heat transfer coefficient using the mean of the steam and water temperatures respectively or if by individual coefficients it refers to one at the inlet and one at the outlet and from those two determine an overall coefficient. Instructions say to use the film temperature which I've been taking as the average between the means since I have nothing else to work with, hence my doubt of whether I can obtain an individual coefficient for the inlet and one for the outlet or if that's a mistake. Any help would be greatly appreciated. If any more information is required please let me know. Thank you.

Why don't you run the numbers for the local overall heat transfer coefficients at the inlet and outlet and see how they compare? But, in terms of interpreting your assignment, I think they are referring to the value averaged over the length, based on the average of the inlet and outlet temperatures. This is how it is usually done. So compare that with the local numbers at inlet and outlet, and see how they compare.