A double-pipe, counter current heat exchanger is used to cool saturated steam at 2 bar (T_s = 120°C) to a saturated liquid. At this temperature and pressure, the inlet volumetric flow rate of steam is 2.42 m³/m, the density of steam is 1.13 kg/m³, and the enthalpy of vaporization of steam is 2201.6 kJ/kg. Cooling water enters the tube side at a rate of 1 kg/s at a temperature 20°C. In independent experiments, the heat-transfer coefficient for steam on the shell side was determined to be 500 W/m² · K. The tube wall is made of copper, thus thermal conduction resistances can be neglected.
a. What is the heat load on the heat exchanger and the outlet temperature of the cooling water?
b. It is desired to achieve a Reynolds number of 20,000 inside the tube. What is the inner diameter of the tube needed, and what is the overall heat-transfer coefficient?
c. What is the required heat-transfer area for the heat exchanger?