Numerical simulation of double-phase coupled heat transfer process of horizontal-tube falling film evaporation

The double-phase coupled heat transfer process plays an important role in the horizontal-tube falling film evaporation. The method of element sliced out of tube was presented and the continuous double-phase transformation was represented by the discrete mass fraction of steam in the tube. The model of the double-phase coupled heat transfer of the horizontal-tube falling film evaporation was built up to simulate the process of coupling heat-transfer process inside and outside tube. The Volume of Fluid (VOF) method was applied to investigate the influence of the spray density on the distributions of the film thickness and the circumferential and axial heat transfer coefficient of horizontal-tube. The computation results showed that the circumferential film thickness changed constantly. The minimum film thickness appeared approximately at the angular positions of 100-140°. And dry spot would form at the bottom of the horizontal-tube. The external film heat transfer coefficient of circumferential horizontal tube gradually decreased. In the axial direction the overall heat transfer coefficient was mainly impacted by the internal film heat transfer coefficient, which was improved with the increasing of water vapor condensation and not sensitive to the spray density.