Acounter-flow, double-tube (shell-and-tube) heat exchanger is used to cool the lubricating oil for large industrial gas turbine engine by cooling water which enters the heat exchanger at 30°c the copper inner tubes have a diameter of 2 cm and negligible thickness, while the inner diameter of the outer annulus (the shell) is 4 cm. water flows through the tube at a rate of 0.18 kg/s, and the oil through the shell at a rate of 0.12 kg/s. the inlet and outlet temperatures of oil are 95°c and 65°c, respectively. assume the tube wall resistance, fouling factors and heat loss to the surroundings are negligible. design the heat exchanger.