Keywords: desalination, horizontal tube evaporator, tube bundles, heat transfer enhancement, liquid film evaporation, liquid collectors, evaporation heat transfer, water spray, heat transfer coefficient
Heat transfer enhancement of falling film evaporation on a horizontal tube bundle
The enhancement of the evaporation heat transfer coefficient is important for the design and operation of horizontal tube spray film evaporators. The water spray on a horizontal tube bundle is numerically studied in steady state conditions. The objective of the present work is to numerically study the effect of the tube configuration and the operating conditions on the evaporation heat transfer coefficient. In addition, the enhancement of the evaporation rate ratio by constructing a water collector around the bottom-heated tube is also numerically studied. In order to evaluate the evaporation rate ratio and the heat transfer coefficient of the falling liquid film on the horizontal tube bundle, the nondimensional governing equations of the mass, momentum and energy of the created liquid film around the hot tube surface are solved numerically using the finite difference method. The results show that the evaporation rate ratio is mainly increased by increasing both the surface temperature and the tube's outer diameter. The evaporation rate ratio enhances by decreasing the chamber pressure and inlet liquid subcooling. The falling distance has little influence on the evaporation rate ratio. Moreover, constructing a water collector around the bottom-heated tube enhances the evaporation rate ratio. The increase in the evaporation rate ratio increases by higher heat flux and also by larger the gap between the collector and the tube surface.