Question

Saturated water vapor has a flow rate of 1.5 kg/s and a pressure of 0.51 bar. The vapor is to be completely condensed to saturated liquid in the shell of a shell-and-tube heat exchanger. In this case, the water vapor enters and the water exits at the same temperature, which represents a case with infinitely high m_dot * Cp for this condensing steam application. On the tube side, city water is used as the cold fluid. The city water enters the thin-walled tubes at 17°C and leaves at 57°C. Assume an overall heat transfer coefficient of 2000 W/m2-K.

After extended operation, fouling causes the overall heat transfer coefficient to decrease to 1000 W/m2-K, and to completely condense the vapor, there must be a reduction in the vapor flow rate. For the same inlet temperature of the city water and flow rate of the city water, calculate the following:

11. Fouled NTU = ?
12. Fouled epsilon = ? (No need for derivation. Use the provided equation for Cr = 0)
13. Fouled qmax = ? Is there a reason for fouled qmax to be different from the clean qmax?
14. Fouled q = ?
15. What is the vapor flow rate required for complete condensation in the fouled exchanger?

Answer 1

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