How is the correct heat transfer equation in the Simscape block "Pipe (TL)"?

Hello,

I need some help in understanding the calculation of the heat transfer in the block "Pipe (TL)" in SimScape. In the source code script “pipe_base.ssc” I found the heat transfer equation: Q=h*A*(T_w-T). In the Simscape documentation I found that T is defined as liquid temperature in the pipe. So far, so good. But I made some investigations with test runs and found out that T is actually same the temperature of the pipe exit T_B, so that I can write the equation above as Q=h*A*(T_w-T_B). But isn’t this assumption, that the liquid temperature is same as the exit temperature, far too inaccurate? For the heat transfer equation shouldn’t be used the logarithmic average of the liquid temperature like shown in the chapter G1 of the VDI Heat Atlas? Or have I missed something in my observations?

Thanks in advance!

Answer 1

[Yifeng Tang]

The temperature at the outlet port will be the same as the temperature inside the pipe. So usually either T_A or T_B will be the same as T_I, and which one depends on the direction of the flow. This is the upwind scheme described here:

https://www.mathworks.com/help/hydro/ug/simscape-fluids-numerical-scheme.html

All components in the foundation library are "bulk" models, meaning there is only one internal state (P, T, etc). If you'd like to model the effect of temperature varying inside the pipe and then the integral effect of temperature difference, consider using the heat exchanger blocks in Simscape Fluids. Althernatively, you can use multiple pipe blocks in series.