Heat Transfer Coefficients: Free and Forced Convection

In summary, the individual and overall heat transfer coefficients for a vertical cylinder with water flowing on the inside and steam on the outside need to be determined for the cases of free and forced convection. With only four temperatures and steam pressure available, Nusselt correlations are being used. There is confusion about whether a single heat transfer coefficient should be calculated using the mean of steam and water temperatures, or if individual coefficients at the inlet and outlet should be determined and then used to calculate an overall coefficient. The instructions suggest using the film temperature, which is being taken as the average between the means due to lack of other information. It is recommended to compare the local overall heat transfer coefficients at the inlet and outlet to the value averaged over the length, based
  • #1
Monochromoton
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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.
 
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  • #2
Monochromoton said:
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.
 

Related to Heat Transfer Coefficients: Free and Forced Convection

What is heat transfer coefficient?

Heat transfer coefficient is a measure of the rate at which heat is transferred from one medium to another. It is defined as the amount of heat transferred per unit area per unit time divided by the temperature difference between the two mediums.

What is free convection?

Free convection is a type of heat transfer where heat is transferred between a solid surface and a fluid (liquid or gas) due to the natural movement of the fluid caused by density differences. This occurs without any external force or fan.

What is forced convection?

Forced convection is a type of heat transfer where heat is transferred between a solid surface and a fluid (liquid or gas) due to the movement of the fluid caused by an external force, such as a fan or pump.

What factors affect heat transfer coefficients?

The factors that affect heat transfer coefficients include the nature of the fluid, the properties of the solid surface, the velocity of the fluid, the temperature difference between the fluid and the surface, and the geometry of the surface.

How do you calculate heat transfer coefficient?

The heat transfer coefficient can be calculated using the equation h = q/(A * ΔT), where h is the heat transfer coefficient, q is the heat transfer rate, A is the surface area, and ΔT is the temperature difference between the two mediums.

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