NUMERICAL STUDY OF EVAPORATION EFFECTS ON HEAT TRANSFER IN FALLING FILM

Prediction of the falling film flow regime has a significant role in design and optimization of absorption chillers. A numerical study has been performed to calculate the falling film physics. The main purpose of this study is calculation of heat transfer and phase change conditions from liquid to vapor. To consider the phase change and phase interaction simultaneously, Eulerian-Eulerian model has been applied. Furthermore, the effect of tube wall temperature changes on convection heat transfer has been studied. To model the disturbances a turbulence model has been used. Numerical modeling has been done for both water and lithium-bromide solution in constant wall temperature condition and the results have been compared and validated with some experimental and numerical studies. The results show the effect of vapor motion on heat transfer coefficient. Regarding present results, vaporization on the tube surface acts as a resistance against heat transfer and reduces it. In addition, vapor motion in the sub layer of the falling film moves away the liquid from hot surface which in turn reduces the total heat transfer coefficient.

کلیدواژه ها:

Heat Transfer ، Absorption Chiller ، Phase Change ، Falling Film ، Li-Br Solution