An endoreversible heat engine driven refrigeration cycle based on the combination of an absorption cycle with vapor and ejector compression cycles is described. This integration maximizes the performance of the conventional ejector and absorption cycles and provides high performance for refrigeration. The analysis shows that the combined cycle has a significant increase in system performance over the heat engine driven vapor compression refrigerators and heat engine driven combined vapor compression and absorption refrigerators.
In order to raise the availability of energy sources, decrease the environmental pollution of high temperature waste heat and develop high performance systems, combined refrigeration cycles have been adopted by the HVAC and R industry. There are three main types of refrigeration systems: vapor compression, absorption and ejector compression. Investigations show that vapor compression cascading is useful where large temperature ranges are encountered [1]. Optimal performances of an endoreversible and irreversible two stage vapor compression refrigerator (VCR) cycles are investigated by many authors [2], [3], [4] and [5]. Absorption refrigerator (AR) and ejector refrigerator (ER) cycles are three heat source systems, and they exhibit continuous and stable operation under part load conditions from 0 to 100%. Compared with the VCR cycle, they have the advantage of using thermal energy from waste heat and other low grade heats. The theory and technology of AR and ER cycles have been developed in recent years [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21] and [22]. While the coefficient of performance (COP) of a VCR cycle is typically 2–4, the COPs of AR and ER cycles are in the ranges 0.5–0.8 and 0.2–0.5, respectively. For enhancing the COP and cooling capacity of thermal energy powered systems, combined AR/ER, VCR/AR and VCR/ER cycles are suggested by many authors [23], [24], [25], [26], [27] and [28]. The heat engine (HE) driven VCR systems generally consume electric energy with the consequences of emission of large amounts of CO2 and NOx. Also, the COP values for HE driven VCR systems are relatively low compared with combined refrigeration cycles [29] and [30]. From the literature survey, it appears that none of the previous investigations concerned a HE driven combined VCR/AR/ER system for refrigeration to improve performance. In the present study, the optimum performance of an endoreversible HE driven combined VCR/AR/ER cycle is investigated. For this purpose, we define a cyclic model which includes the irreversibility resulting from the finite rate of heat conduction and use it for optimization of performance.
The present study evaluates the optimum performance of an endoreversible heat engine driven combined vapor compression absorption and ejector cycle for refrigeration. This combined cycle brings together the advantages of conventional refrigeration systems. The simulation results show that the combined cycle has a significant increase in system performance over conventional systems. Its COP value is at least 14% higher than its sub-systems (see Table 2). Since the combined system is internally reversible, the resulting COP ε obtained by the present analysis, Eq. (69), is the maximum overall coefficient of performance for the combined system under consideration. Therefore, ε can be used as a standard of comparison. As a further consideration, our model provides a reasonable criterion for use in evaluation of the performance of real heat engine driven combined VCR/AR/ER cycles.
