(Solved): Question-4 a) Define the effectiveness of a heat exchanger and list the factors in which the effect ...

Question-4 a) Define the effectiveness of a heat exchanger and list the factors in which the effectiveness of a heat exchanger depend on. (4 marks) b) The specific heat and inlet temperature of the hot water enters 3 cm internal diameter tube of a double-pipe counter-flow heat exchanger as shown in below FIG Q4b are 4180 J/kg.K and 30° C respectively. The water enters at a rate of 2.4 kg/s. This water is heated by steam condensing at 140°C (hig = 2145 KJ/kg) in the shell. If the overall heat transfer coefficient of the heat exchanger is 700 W/m².K 140°C Steam 90°C Water 30°C 2.4 kg/s 140°C FIG Q4b Determine the length of the of the tube required in order to heat the water to 90°C by using i) LMTD method (5 marks) ii) Effectiveness (?- NTU) method. (5marks) c) A plane wall with surface temperature of 350°C is attached with straight rectangular fins of k = 235 W/m-K as shown in below FIG Q4c. The fins are exposed to an ambient air condition of 25°C and the convection coefficient is 154 W/m².K. Each fin has a length of 50 mm, a base of 5 mm thick, and a width of 100 mm. c) A plane wall with surface temperature of 350°C is attached with straight rectangular fins of k = 235 W/m-K as shown in below FIG Q4c. The fins are exposed to an ambient air condition of 25°C and the convection coefficient is 154 W/m².K. Each fin has a length of 50 mm, a base of 5 mm thick, and a width of 100 mm. T, = 350 °C i) ii) iii) k=235 W/m-°C L=50 mm Determine the following Air, 25 °C h=154 W/m².C FIG Q4c The efficiency of fin Heat transfer rate for a single fin Effectiveness of each fin w = 100 mm = 5 mm (6 marks) (3 marks) (3 marks)