oa Thermodynamic Analysis Of Heat And Mass Transport Phenomina In Phase Change Regenerators With Conductive Packing

This paper discusses a comparative study on the role of conductive packing in Humidification-Dehumidification (HDH) solar desalination cycles under steady state conditions. Experimental and theoretical studies have been performed at the Technical University of Munich, Germany on HDH desalination system equipped with phase change material (PCM) encapsulated in spherical plastic shells and used as a conductive packing media in the evaporator and condenser. Moreover, a solar collector and an external PCM thermal storage are used to drive the HDH plant. The external PCM thermal storage is used to guarantee continuous operation of the plant day and night round the clock under the transient behaviour of solar irradiation. The objective of using PCM elements in the evaporator and condenser was for heat storage as a backup during cloudy hours or for part-time night operation. During analysis of steady state conditions, it was discovered that the PCM packing media seem to enhance their thermal performance through locally establishing multiple-effects of heating/humidification (MEHH) and cooling/dehumidification (MECD) while air passing through the successive packing layers in the evaporator and condenser respectively. The multiple-effect phenomena are attributed solely to existence of conductive packing media, which act as heat and mass exchangers. Thus, the focus of the study lies on the thermal conductivity rather than the thermal capacity or solid-liquid phase change processes of the packing in the two columns. The performance of the evaporator and condenser technologies filled with PCM as a conductive packing was examined experimentally in comparison with empty spherical shells with the same size as well as with a conventional industrial plastic packing with high specific surface area. Comparisons were made between different packing types under similar operating conditions to examine the thermal behavior of the evaporator and condenser at atmospheric pressure. Transient simulation models for the individual components in the HDH system have been established and validated against experimental measurements. Using both experiment and simulation, a detailed heat and mass transfer analysis for the performance of the evaporator and condenser over a wide range of operation conditions under steady state has been performed using different types of packing materials. Furthermore, a yearly parametric analysis for the whole HDH plant has been performed under real weather conditions for two locations in Egypt. The overall performance analysis focuses on the optimum operation conditions of the HDH system, with optimum conductive filling material, with and without external PCM thermal buffer.