This paper aims to design a special exchanger to recover the exhaust gas heat of marine diesel engines used in small and medium-sized fishing vessels, which can then be used to heat water up to 55°C-85°C for membrane desalination devices to produce fresh water. A new exhaust-gas heat exchanger of fins and tube, with a reinforced heat transfer tube section, unequal spacing fins, a mixing zone between the fin groups and four routes tube bundle, was designed. Numerical simulations were also used to provide reference information for structural design. Experiments were carried out for exhaust gas waste heat recovery from a marine diesel engine in an engine test bench utilizing the heat exchanger. The experimental results show that the difference between heat absorption by water and heat reduction of exhaust gas is less than 6.5%. After the water flow rate was adjusted, the exhaust gas waste heat recovery efficiency was higher than 70%, and the exhaust-gas heat exchanger's outlet water temperature was 55°C-85°C at different engine loads. This means that the heat recovery from the exhaust gas of a marine diesel engine meets the requirement to drive a membrane desalination device to produce fresh water for fishers working in small and medium-sized fishing vessels.

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