MODELING OF HEAT AND MASS-TRANSFER IN A HORIZONTAL-TUBE FALLING-FILM EVAPORATOR FOR WATER DESALINATION

In this study, heat and mass transfer in a horizontal-tube falling-fil m evaporator, destined to be used in a desalination plant functioning by aero-evapo-condensation process, is studied theoretically. The pres ent exchanger is made of polypropylene and it was designed to work at low temperatures (60 degrees C-90 degrees C) utilising geothermal ener gy. The one-dimensional model developed, uses basic aerodynamic, hydro dynamic and heat/mass transfer information to predict the performance of the exchanger. The predicted transfer characteristics obtained from the simulations are compared with experimental data. From this compar ison it can be learnt that the model is well able to predict the trend s of heat and mass characteristics of the evaporator. However, in low liquid film now rate conditions, the model was found to overpredict th e transfer characteristics slightly and the reasons for the difference s are discussed. The influence of the different thermal, hydrodynamic and geometric parameters on the evaporator performances was investigat ed. The variations of the distilled water amount inside the exchanger are analysed. The results are used to determine the operational condit ions corresponding to a maximum evaporative performances. The model wa s also used to optimise the different components of the exchanger.