Chapter 7, Problem 7.32P

Saturated steam at a gauge pressure of 2.0 bar is to be used to heat a stream of ethane. The ethane enters a heat exchanger at 16°C and 1.5 bar gauge at a rate of 795 m³/min and is heated at constant pressure to 93°C. The steam condenses and leaves the exchanger as a liquid at 27°C. The speci?c enthalpy of ethane at the given pressure is 941 kJ/kg at 16°C and 1073 kJ/kg at 93°C.

(a) How much energy (kW) must be transferred to the ethane to heat it from 16°C to 93°C?

(b) Assuming that all the energy transferred from the steam goes to heat the ethane, at what rate in m³/s must steam be supplied to the exchanger? If the assumption is incorrect, would the calculated value be too high or too low?

(c) Should the heat exchanger be set up for cocurrent or countercurrent ?ow (see the following schematic diagram)? Explain. (Hint: One of them will not work at all.)