申論題

1. A counter-flow double-pipe heat exchanger is to heat water from 30 ℃ to 90 ℃  at a rate of 1.2 kg/s. The heating is to be accomplished by heating liquid at 160℃  at a mass flow rate of 2 kg/s. The inner tube is thin-walled and has a diameter of 15 mm. If the overall heat transfer coefficient is 640 W/m²K, c_p of water is 4.2 KJ/ kg K, c_p of heating liquid is 5 kJ/kg K, please determine: