Hot oil (c, 2200 J/kg.K) is to be cooled by water (cp 4180 J/kg.K) in a 2-shell-passes and "N-tube-passes" heat exchanger. The tubes are thin-walled and are made of copper

with a diameter of 1.8 cm. The length of each tubepass in the heat exchanger is "L" m, and the overall heat transfer coefficient is 340 W/m?.K. Water flows through the tubes at a total rate of 0.1 kg/s, and the oil through the shell at a rate of 0.2 kg/s. The water and the oil enter at temperatures 18 °C and 160 °C, respectively. Design a heat exchanger if it is desired to heat the water to 80 °C.