Question

How does flow rate affect the individual heat-transfer coefficients on the tube and annular sides of the exchanger? Explain in words and show the equations necessary to calculate these individual heat transfer coefficients as well as the overall heat transfer coefficient. 3.

Answer 1

The local heat transfer coefficient increases as the mass flow rate increases. The heat flow from the pipe wall in a length dx is

$\dot{q}\pi Ddx=h\pi D(T_{0}-T)dx$

After the integration from limits T1 (temperature at inlet x=0) to T in a length 0 to x

To-T 4h.r Pum CpD

The temperature at the exit of the heat exchanger is T= T2 at x=L

4hL rl

The overall heat transfer coefficient is constant throughout the heat exchanger as per the LMTD assumption.

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