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CraigH
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Are these statements true? (Regarding heat flow)
I'm revising for an exam, and this is what I think I know so far.
It will really help if someone can confirm these statements for me.
Consider an iron pipe with inner diameter 20mm and outer diameter 30mm. The inside surface of the pipe is maintained at 100 degrees celsius, and the outside surface is at 90 degrees celsius. Air is flowing past the outside of the pipe at temperature 20 degrees celsius.
Are these statements true:
Thank you!
I'm revising for an exam, and this is what I think I know so far.
It will really help if someone can confirm these statements for me.
Consider an iron pipe with inner diameter 20mm and outer diameter 30mm. The inside surface of the pipe is maintained at 100 degrees celsius, and the outside surface is at 90 degrees celsius. Air is flowing past the outside of the pipe at temperature 20 degrees celsius.
Are these statements true:
- The heat flow dQ/dt from the inside of the pipe to the outside of the pipe (through the iron) equals the temperature difference (between the inside and outside surface of the pipe), divided by the thermal resistance of the pipe
- The thermal resistance of the pipe (per meter) is given by (ln(r2/r1))/(2*pi*k) where k is the thermal conductivity of the pipe
- The heat flow dQ/dt from the outside of the pipe to the air equals the outside area of the pipe, multiplied by the temperature difference (between the air and the outside of the pipe), multiplied by the heat transfer coefficient between the air and the pipe
- The heat transfer coefficient between the air and the pipe can be found/estimated using the Reynolds number, the Prandtl number, and the thermal conductivity of the air
- The Reynolds number will depend on mainly the velocity of the air
- The Prandtl number will depend mainly on the specific heat capacity of the air
- If the heat flow from the inside to the outside of the pipe equals the heat flow from the outside of the pipe to the air, the temperature on the outside of the pipe will be constant
- If the heat flow from the inside to the outside of the pipe is greater than the heat flow from the outside of the pipe to the air, the temperature on the outside of the pipe will be increasing.
Thank you!
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