Part-2 (70%) A food factory uses hot water to wash and clean foods. The drained water, which has a mass flow rate of 0.1 kg/s, still have a temperature of 62°C. Consider a concept design solution of waste heat recovery for pre-heating fresh water, which has an inlet temperature of 15°C and mass flow rate of 0.2 kg/s inside tube flow. The following information can be used for your design: • 2 shell-pass and any multiple of four tube passes (4, 8, 12, etc., tube passes) heat exchanger may be considered. The shell side heat transfer coefficient could be assumed as 300 W/m²K. • The most popular copper pipe of 15 mm internal diameter could be used. Total pipe length should not be longer than 60 meters. • For inside pipe flow, fully developed turbulent flow and Dittus and Boelter correlation may be assumed, Nu = 0.023Re 0.8 pr.n 0.7 ≤ Pr ≤ 160 Re > 10,000 where n = 0.4 for heating, n = 0.3 for cooling of fluid flowing through the tube A clear justification of the heat exchanger design and calculations should be included, also to state why it should be deployed in terms of energy saving. Assumptions: steady operating conditions, the heat exchanger is well insulated, properties are constant, the thermal properties for the shell side water can be assumed based on 45°C, and the thermal properties in tube side water can be assumed based on 25°C; no kinetic & potential energies changes, the overall heat transfer coefficient is constant, the thickness of the tube wall is negligible. (NB: The total cost of the heat exchanger including the installation could be about £30k, and the factory may not be interested in any project that has a payback period of more than 2.5 years. If the cost of natural gas is 30 pence per kWh.)