Leila Zili-Ghedira

A TRANSIENT STUDY OF COUPLED NATURAL CONVECTION AND RADIATION IN A POROUS VERTICAL CHANNEL USING THE FINITE-VOLUME METHOD

The present article deals with a numerical study of coupled fluid flow and heat transfer by transient natural convection and thermal radiation in a vertical channel opened at both ends and filled with a fluid-saturated porous medium. The bounding walls of the channel are isothermal and gray. In the present study we suppose the validity of the Darcy law and of the local thermal equilibrium assumption. The radiative transfer equation (RTE) is solved by the finite-volume method (FVM). The net radiative heat flux as well as its divergence is also calculated using the same method. The sensitivity of the fluid flow and the heat transfer to different controlling parameters, namely the conduction-radiation parameter or Planck number or Stark number, N, the optical thickness, τ D , and the wall emissivity, ϵ, are addressed. The results indicate that the controlling parameters of the problems, namely, N , τ D , and ϵ, have significant effects on the flow and thermal fields and on the transient process of heating or cooling of the medium. It has also been shown that the volumetric flow rate, q v , and the convected heat flux at the channels exit increase when N is decreased and/or τ D and ϵ are increased.

Mathematical Modeling of Heat and Mass Transfers in Humidifiers

Humidifiers are widely used in several domains such as water desalination by humidification–dehumidification, cooling towers, air conditioning, etc.

Desiccant-based dehumidification and direct/indirect evaporative cooling technologies

Desiccant cooling systems are energy efficient and allow a better indoor air quality. Desiccant dehumidification is profitable in handling latent heat, easy to be reactivated with low-grade energy, like solar energy and waste heat, etc. The exploitation of heat produced by solar thermal collectors is a motivating option for thermal driven Desiccant cooling air conditioning processes. It is a good solution to guarantee less environmental impact. Desiccant cooling systems have two air streams. The first stream is the process air delivered to conditioned space, and the second stream is the reactivation air used to regenerate desiccant material. For this reason tow important phenomena are mentioned and studied: dehumidification in order to match indoor comfort criteria and humidification to produce the cooling effect. In this work, different configuration of desiccant cooling installation are studied and compared. The study focused on the cooling branch of each configuration. The principal components used in the different configurations presented are; desiccators, heat exchanger and a humidifier. The objective of this study is to evaluate the more efficient system to be used. For this aim a numerical tool was used. The reliability and efficiency of the numerical tool established was tested and validated by comparison against data collected from literature.