# Wall temperature of pressure cylinder - Boundary condition

I have a thick-walled pressure cylinder, that transports fluid and experiences only internal pressure. During the process, the outer wall temperature is measured. And I have no clue about the inner wall temperature. The only fact, that I know is, the temperature on the outer wall is due to inner wall temperature that is conducted outside. So, the inner wall temperature should be always greater than that of outer wall.

Now I would like to reproduce the same situation in a simulation software by providing the outer wall temperature as input and read out the inner wall temperature data on the corresponding nodes. To do this, I am applying surface loads on the outer wall, which is the measured value as the boundary condition. But with this I see the inner wall temperature are always lesser than the outer wall temperature.

When I tried to give the internal pressure as boundary condition for the inner wall, the software says, pressure data for the given nodes are not required. Any idea about, where am i going wrong, or what am i missing? thanks in advance

• What is the temperature of the fluid arriving? – Solar Mike Jul 3 '19 at 10:49
• Either you model the complete heat flow process, from the fluid into the pipe and then through the outside wall, or you prescribe all the boundary temperatures. Either way, if heat is supposed to flow from the fluid to the outside of the pipe, you need some boundary conditions that represent the heat source, as well as the heat sink at the outside of the pipe. – alephzero Jul 3 '19 at 13:40

Assuming the most basic situation, steady-state conduction, you could use the equivalent resistance equation: $$Q = (T_1-T_2)/R$$
Where $$Q$$ is heat transfer rate, $$T_1$$ is heat source, $$T_2$$ is heat sink, and $$R$$ is the thermal resistance which is related to material and geometry. As the equation shows, pressure is not a factor.