Problem 1: In a food processing plant a brine solution is heated from 6oC to 12oC in a double-pipe heat exchanger by water entering at 50oC and leaving at 40oC at the rate of 0.166 kg/s. If the overall heat transfer coefficient is 850 W/m2-oC, what heat exchanger area is required for-
(a) What heat exchanger area is required for parallel flow?
(b) What heat exchanger area is required for counter flow?
Problem 2: A double-pipe, parallel flow heat exchanger uses oil (cp = 1.88 kJ/kg-oC) at an initial temperature of 205oC to heat water, flowing at 225 kg/h, from 16oC to 44oC. The oil flow rate is 270 kg/h.
(a) What heat exchanger area is required for an overall heat transfer coefficient of 340 W/m2-oC?
(b) Determine the number of transfer units (NTU).
(c) Calculate the effectiveness of the heat exchanger.
Problem 3: a) Estimate the heat transfer from a 40 W incandescent bulb at 127oC to 27oC quiescent air. Approximate the bulb as a 50 mm diameter sphere.
b) What percentage of the power is lost by free convection?
Problem 4: Air at 27oC flows normal to a 77oC, 30 mm outside diameter water pipe. The air moves at 1.0 m/s.
(a) Estimate the heat transfer per unit length.
Problem 5: Consider atmospheric air at 25oC and a velocity of 25 m/s flowing over both surfaces of a 1-m long flat plate that is maintained at 125oC.
1. Determine the rate of heat transfer per unit width from the plate for values of the critical Reynolds number corresponding to 105, 5x105, and 106.
Problem 6: A shell-and tube heat exchanger (two shells, four tube passes) is used to heat 10,000 kg/h of pressurized water from 35 to 120oC with 5000 kg/h pressurized water entering the exchanger at 300oC.
(a) If the overall heat transfer coefficient is 1500 W/m2-K, determine the required heat exchanger area.