Chapter 11

Classify heat exchangers according to flow type and explain the characteristics of each type.

When is a heat exchanger classified as being compact? Do you think a double- pipe heat exchanger can be classified as a compact heat exchanger?

What is a regenerative heat exchanger? How does a static type of regenerative heat exchanger differ from a dynamic type?

What is the role of the baffles in a shell-and-tube heat exchanger? How does the presence of baffles affect the heat transfer and the pumping power requirements? Explain.

How does a cross-flow heat exchanger differ from a counter-flow one? What is the difference between mixed and unmixed fluids in cross-flow?

What are the heat transfer mechanisms involved during heat transfer in a liquid-to-liquid heat exchanger from the hot to the cold fluid?

Under what conditions is the thermal resistance of the tube in a heat exchanger negligible?

Consider a double-pipe parallel-flow heat exchanger of length $L$ The inner and outer diameters of the inner tube are $D_1$ and $D_2$, respectively, and the inner diameter of the outer tube is $D_3$. Explain how you would determine the two heat transfer surface areas $A_i$ and $A_o$. When is it reasonable to assume $A_i\approx A_o\approx A_s$ ?

How is the thermal resistance due to fouling in a heat exchanger accounted for? How do the fluid velocity and temperature affect fouling?

In a thin-walled double-pipe heat exchanger, when is the approximation $U=h_i$ a reasonable one? Here $U$ is the overall heat transfer coefficient and $h_i$ is the convection heat transfer coefficient inside the tube.