Résumé: A theoretical investigation is presented about a double evaporator ejector refrigeration cycle (DEERC). Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger (IHX). The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure. Moreover, the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor. To assess accurately the influence of the IHX on the DEERC performance, a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors. The model also accounts for the friction effect in the ejector mixing section. The equations of this model are solved using an Engineering Equation Solver (EES) for different fluids. These are: R134a as baseline fluid and other environment friendly refrigerants used for comparison, namely, R1234yf, R1234ze, R600, R600a, R290, R717 and R1270. The simulation results show that the DEERC with an IHX can achieve COP (the coefficient of performance) improvements from 5.2 until 10%.

Résumé: In order to evaluate the performance of a hybrid compression / éjection réfrigération sj'stem using solar energy at low or médium température, a simulation model of its behavior based on those of its various components has been developed. It includes in particular for the ejector, a 1 -D model of the "constant section mixing" type developed in optimal transition régime. The réfrigérants tested are steam for the ejector loop and the R1234yf (replacing the RI 34a) for the mechanical compression loop. The behavior of the H2O vapor flowing in the ejector is considered that of the perfect gas. The properties of réfrigérants are calculated using REFPROP* software, everywhere else. For a cooling capacity of 10 kW and air conditioning operating conditions, the model allows to détermine the main parametere of the ejector and its entrainment ratio, the thermal and mechanical COP of the whole réfrigération System as well as the necessary surface of the solar coUector. Furthermore, the influence of the température of the boiler, the condenser, the intercooler as well as that of the evaporator on the mechanical COP of the hybrid System and the solar collection surface in particular, were examined. The results highlight that the solar réfrigération System with hybrid cycle compression/éjection using the refrigerants H2O/R1234yf allows an increase of the mechanical COP higher than 50% compared to that of the conventional réfrigération System and thus constitutes an acceptable ecologically System that can compete with the iatter.

Résumé: To investigate the réduction of heat losses on the upper part of a flat solar collector, a two-dimensional study was carried out by CFD analysis using Fluent. For this purpose, the heat transfer behavior in the air gap over a wide range of thicknesses of the latter (1-20 mm) and the addition of a second glass cover fixed at midheight of the air gap spacing have been investigated. For small thicknesses of the air gap (1-8 mm), the heat transfer is essentially conductive. An increase in the thickness leads to the intensification of the natural convection which induces high thermal losses. The simulation results have shown that the addition of a second cover glazing leads to the weakening of the natural convection and thus to an average enhancement of the solar collector température over the range of thicknesses studied of approximately 17%. The overail thermal losses coefficient is then reduced by an average of 26% compared with the single-glazed solar collector. They have also shown that the thickness of the air gaps resulting in the minimum overall heat losses is 8 mm and that the thickness of the second glass cover has no significant effect on thèse results. In addition, this study has highlighted the importance of taking into account the radiation heat transfer in establishing the thermal balance of a flat solar collector. Indeed, this....