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Due to their simplicity, jet-ejector cooling systems have been investigated for different applications despite their lower thermal COP th in comparison to alternative thermally-driven cooling technologies. The present paper aims at the derivation of a simple method of representation of the operation characteristics of a jet-ejector cooling system for changing boundary conditions. Thereto, a jet-ejector cooling system operating with the refrigerant R134a has been experimentally investigated in double choking operation of the jet-ejector. The jet-ejector operation is characterized by the entrainment ratio μ in dependence of the adequate stagnation pressure ratios. The results are discussed in a non-dimensional graph as a three dimensional surface from which characteristic lines may be deduced. In several graphs, the motive, condenser and evaporator pressures are linked with the entrainment ratio μ , the cooling capacity Q ˙ 0 , the thermal COP th and the hydraulic COP h allowing a comprehensive determination of the system operation. [ABSTRACT FROM AUTHOR]

Abstract: Heat pumping devices which are operating on sorption effects comprise at least two times two categories, namely liquid or solid sorption cycles on the one hand, and open or closed cycles on the other hand. For the benefit of energy saving and the environment as well as for the further development of the technology it is important to be able to compare and evaluate these options in the context of the respective application. Some ideas to this end are shown in this paper. First the meaning of temperatures and humidity for the difference between open and closed systems is discussed, and there are a lot of similarities. Then some differences between solid and liquid sorption which are especially important for the question of minimum operating temperature and part load behavior are being reviewed, and we find that there is something to learn, mutually. Finally the consequences of solar fraction, auxiliary power consumption, and cogeneration efficiency are being highlighted, in order to check the perception of sorption systems to be environmentally benign. These consequences are important for all kinds of sorption cooling systems. It can be expected that there are significant improvements in the efficiency of power plants and compression cooling systems; consequently we find that sorption technology must improve its performance considerably also in order to stay competitive. [Copyright &y& Elsevier]

Abstract: This paper is the first of two which presents the development of a dynamic model for single-effect LiBr/water absorption chillers. The model is based on external and internal steady-state enthalpy balances for each main component. Dynamic behaviour is implemented via mass storage terms in the absorber and generator, thermal heat storage terms in all vessels and a delay time in the solution cycle. A special feature is that the thermal capacity is partly connected to external and partly to internal process temperatures. In this paper, the model is presented in detail. For verification, the model has been compared to experimental data. The dynamic agreement between experiment and simulation is very good with dynamic deviations around 10s. General functionality of the model and a more detailed comparison with experimental data are presented in Part II of this paper. [Copyright &y& Elsevier]

The performance of an advanced triple-pressure level (TPL) single-stage absorption cycle with refrigerant R125 and various organic absorbents were studied. In the developed TPL cycle, a jet ejector of a special design is added at the absorber inlet. The device serves two major functions: it facilitates pressure recovery and improves the mixing process between the weak solution and the refrigerant vapor coming from the evaporator. These effects enhance the absorption process of the refrigerant vapor into the solution drops. To facilitate the design of a jet ejector for absorption machines, a numerical model of simultaneous heat and mass transfer between the liquid and the gas phases in the ejector was developed.Based on the computerized simulation program, a parametric study of a TPL cycle was carried out. Comparison was made between the performances of the TPL and the common double pressure level (DPL) absorption cycle with refrigerant R125 and various organic absorbents. In addition, the influence of the jet ejector on the performance of the absorption cycle and the size of the unit was studied. [Copyright &y& Elsevier]