Answer Happy

Consider the heat exchanger design of Example 11.3, that is, a finned-tube, cross-flow heat exchanger with a gas-side overall heat transfer coefficient and area of 100 W/m²K and 40 m², respectively. The water flow rate and inlet temperature remain at 1 kg/s and 35°C. However, a change in operating conditions for the hot gas generator causes the gases to now enter the heat exchanger with a flow rate of 1.5 kg/s and a temperature of 250°C. What is the rate of heat transfer by the exchanger, and what are the gas and water outlet temperatures? SOLUTION Known: Hot and cold fluid inlet conditions for a finned-tube, cross-flow heat exchanger of known surface area and overall heat transfer coefficient. Find: Heat transfer rate and fluid outlet temperatures. Schematic: Tu - 250°C A-40 m U - 100 W/mK Which method? -1.5 kg's LMTD -To = 1 kg's or E-NTU •The T.,- 35°C Assumptions: 1. Negligible heat loss to surroundings and kinetic and potential energy changes. 2. Constant properties (unchanged from Example 11.3).