الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 81 |  |  |
| | | from | 81 | | |
Abstract
Through the recent decades, many studies have focused on finding efficient methods to enhance the heat transfer performance in Falling film on horizontal tube evaporators of the Multi-Effect Distillation (MED) desalination systems. Owing their major role in heat and mass transport, as well as the system’s productivity. The reduction in film thickness greatly contributes to the behaviour of the film and the properties of heat and mass transfer processes. And it is mainly influenced by the intertube spacing, circumferential angle, tube shape and diameter, and the film’s Reynolds number. The present study seeks to discuss numerically the falling film thickness around the horizontal tube in MED evaporators. Computational fluid dynamics (CFD) models using ANSYS software are developed in order to investigate heat and mass transmission properties, liquid falling film behaviour, and thickness distribution surrounding circular horizontal tubes. Simulations are investigated using a domain of only two inline tubes with different outer diameters, to simulate the behaviour of a falling film at circumferential angles ranging from 15 to 165 degrees with intertube spacing up to 40 mm for a constant value of flow rate and under adiabatic condition. In addition, a modification on falling film evaporator tubes is carried out to enhance its thermal performance by wrapping a layer of porous media around the horizontal tubular walls. Porous media is such a simple, efficient, and low-cost technique in enlarging the surface contact area of heat transfer through the fluid pass, so it has been selected in this study for its thermal potential. from the results, by comparing with a bare tube falling film evaporator, we can observe much higher heat transfer performance represented in the average surface Nusselt number (Nu) which can be increased by three times for high Reynolds number and six times for low Reynolds number. Also, simulations are conducted to investigate the effect of varying the porosity ratio of the porous medium added to the tubes in the heat transfer performance. Furthermore, deducing the way to select a decent porosity ratio to be used to get the best thermal performance is demonstrated through the study.