Comparison of Heat and Mass Transfer. in Three Adsorption Solar Reactors


Department of Physics,

Faculty of Sciences B. P. 2121 — Tetouan — Morocco
Fax: (212) 39 99 45 00, E-mail: Aroudam_hass@Hotmail. com


The performance evaluation of 1 m2 area of three type of adsorption solar reactors used in refrigeration are presented. The numerical computation results are obtained relatively for four typical sunshine days characterized by a maximal solar radiation measured locally and shows that both the cycled mass of refrigerant and the thermal performance coefficient of each machine are functions of the height of the porous medium and they are very depending on the meteorological data.

The effect of fins, the offered volume in the porous medium and the meteorological conditions are analysed and shows that the performance of machine is important for the month of April corresponding to some diurnal and nocturnal temperature and a solar radiation favourable for an application. A two-dimensional distribution of temperature and concentration of fluid inside the rectangular configuration is also presented along a daily cycle. The physical model adopted use the mass and heat balance equations and the Dubinin — Radushkevich formula for the determination of fluid desorbed fraction in each element of the discretised medium of the porous medium at a constant pressure.

Key Words: Adsorption — cooling machine — Solar reactor — Ammonia — Activated carbon

1. Introduction

The product of cooling energy by applying solar energy in the isolate site favoured by solar radiation present mainly a great interest. These are very important if the solar system used is very sample and not need a mechanical organ. An application suitable use the systems of adsorption phenomena between a solid and gas for ice production or refrigeration. They differ to other machine by the functioning mode of the collector, which represents the motor organ of the machine. The principle element which represents the thermal motor functioning by adsorption / desorption mode between a solid and a vapour under temperature — pressure variation, allowing to circulate a refrigerant fluid through tubes connecting different elements constituting the machine in the course of a daily cycle. The performance deduction of this machines type is very important by report to the case of absorption cooling machines. The efficiency depends strongly on the expressions of the produced energy quantity and that offered to the system. In the order to improve the performance, many researchers are developed and studies rigorously each component of the solar machines in the aims to enhanced the efficiency. Several experimental and theoretical works have been presented, they focus the objects on the heat transfer, thermal regeneration, the couples thermo physical characteristics, the effect on the environment, recourse to the new mixture, etc [1-12].

The interest of adsorption refrigerator application are increased when new other adsorbent are used such the active carbon fiber (ACF); substitute for activated carbon [13,15]. In this work, we focus on the numerical study of the daily evolution
of temperature, fluid mass and the pressure inside a solar reactor, submitted to real solar radiation data recorded locally. We propose to compute and compare the performances of three solar cooling machines considering rectangular and cylindrical reactors, with and without fins, in order to characterized the obtained cycles under real weather conditions.

We describe solar adsorption cooling machine using ammonia / activated carbon couples and the Dubinin-Raduskevich formula [16] for determination the adsorbed mass of ammonia, and to present a numerical distribution of temperature and adsorbed mass, versus time, inside a reactor heated by variable solar flow. A good design of elements of the compatible machine with the ambient medium, the heat source and the functioning mode allow to improve the efficiency of the refrigerator.

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