A set of experimental facilities were set up to measure overall heat transfer coefficient of horizontal-tube falling film evaporators with triangular, rotated square and square-pitch bundles. Effect of spray density, saturation temperature, total temperature difference and inlet steam velocity on the overall heat transfer coefficient K is studied respectively. The tubes are made of HAL77-2A aluminium brass with an outer diameter of 25.4 mm. Fluids inside and outside the tubes are steam and fresh water respectively. The results indicate that growth of spray density and saturation temperature helps to increase the K. The K could also be increased by reducing the total temperature difference. However, the impact of the inlet steam velocity on the K is less significant. The K in the evaporator with rotated square-pitch arrangement is supreme. Furthermore, space distribution of local overall heat transfer coefficient in the evaporators is also discussed. Based on this investigation, basic engineering design information will be provided to establish the governing parameters for horizontal-tube falling film evaporator in the field of seawater desalination.

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