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# Uncoupled heat transfer analysis

## Uncoupled heat transfer analysis

(OP)
I have a pipe that the product inside is 60oC. half of the pipe is in the water which is 4oC. and half in in the air which is 22oC.

How should I apply the boundary condition to the 3 surface of the pipe (inside pipe, outer pipe in water, outer pipe in air)? in order to output the temperture within the pipe for the stress analysis.

should I apply  by BC - surrounding temperture?
or Load - surface heat flux?

If I need to apply as surface heat flux, how can I calculate it please?

### RE: Uncoupled heat transfer analysis

You apply Temperature BC at the outer surface of the pipe contacting the water (that is the temperature of the water [we assume it fixed])and the Temperature BC at the outer surface of the pipe contacting the Air (that is the temperature of the air [we assume it fixed])and given the thermal properties of the pipe, the temperature and the flux at any point in the pipe (including the inner surface) will be calculated.

### RE: Uncoupled heat transfer analysis

Inside the pipe you'd calculate the heat transfer coefficeint to the medium inside depending on its flow rate and so forth. On the outside I'd set the temperature to the water temperature too, but to the air you have natural convection (from a vertical surface presumably) and radiation to the ambient. It's not a fixed temperature as Cansand says.

corus

### RE: Uncoupled heat transfer analysis

(OP)
The pipe that in the air ios enclosed within a bigger pipe that the outer pipe is in the water.
If I have to consider flow rate inside the pipe, why do i not needed for the water?
If I samplifer the problem by applying temperture to the surface that touch the water and the inner pipe that touch the product. How wrong is my results (assuming the maximum temperture different is only 60oC)

### RE: Uncoupled heat transfer analysis

If the pipe is stood in water that is stagnant then it's reasonable to assume that the pipe outer surface is at the water temperature. If the water is moving due to some convection processs then you might have to calculate a heat transfer coefficient. If the pipe is inside of another pipe then you'd have to consider radiation from one pipe to the other, whilst the outer pipe radiates to the ambient.
If you're not sure then take the worst case possible for maximum stress. In this case that would be maximum temperature differences either through the thickness or mean temperature differences. If your stresses are acceptable for the worst case then a lesser more realistic but unkown case, would also be acceptable too.

corus

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