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In this study, thermodynamic analysis for integration of a PEMFC with an organic Rankin cycle, and an ejector expansion vapor compression refrigeration system is presented. The input energy of the system is supplied by the waste heat of a PEMFC. Energy and exergy analysis is performed on each system component and compared with a simple ORC-VCR without an ejector. The results show that employing the ejector can improve the refrigeration capacity, energy efficiency, and exergy efficiency by 18.88%, 12.29 %, and 12.27%, respectively, compared to a simple ORC-VCR system. Moreover, the overall energy and exergy efficiency of the system is 33.43% and 5.46% higher than a standalone PEM fuel cell. Furthermore, in the parametric study, the effect of condenser temperature, evaporator temperature, ejector efficiency, PEMFC operating temperature, current density, and PEMFC operating pressure on the energy efficiency, exergy efficiency, and refrigeration capacity of the system is investigated. [ABSTRACT FROM AUTHOR]

This study focuses on a combined power generation and cooling system comprising an organic Rankine cycle and a dual evaporator cooling cycle. A parametric study based on exergy analysis was performed using different organic fluids: R134a, R290 and R600 in order to determine its optimal operation. The results show that the thermodynamic parameters that were studied, such as the operating temperature of the evaporator of the ORC cycle and the dual evaporator cycle on the performance of the system are of great importance and improve the performance of the combined system including energy efficiency and exergy efficiency using R600 as the working fluid. Furthermore, the results indicate that using R600 as the working fluid for both cycles improve the system performance. [ABSTRACT FROM AUTHOR]

With the growth of energy-efficient building sector, ventilation systems are becoming increasingly important not only of fresh air supply but also in terms of energy consumption. The aim of this paper is to describe and analyse the operation of an air handling unit (AHU) with a heat pump using energy and exergy analyses under the variable environmental temperature (from –30 °C to 10 °C). The application of selected methods is illustrated in a case study of an AHU using environmental temperatures of Vilnius city during heating season (from the beginning of October to the end of April). An analytical method for determining distribution of the environmental (outdoor air) temperature is used. Energy and exergy analyses showed periods when the highest amounts of energy and exergy were consumed and the greatest exergy losses occurred. This allowed to reveal the component of the system with the highest exergy losses – the heat pump evaporator. Therefore, further research is needed for its design and application. At the end of the article, the seasonal indicators of the AHU with heat pump operation were calculated: coefficient of performance and exergy efficiency. The presented research procedure could be applied to the analysis of other energy systems and processes in them. [ABSTRACT FROM AUTHOR]

Featured Application: Novel combined ORC-VCR cycle and its comparison with usual ORC-VCR cycle are explained. Performance of different working fluids is investigated. Effects of various operational parameters on system performance are shown. This paper presents energy and exergy analysis of two vapor compression refrigeration cycles powered by organic Rankine cycle. Refrigeration cycle of combined system was designed with single and dual evaporators. R134a, R1234ze(E), R227ea, and R600a fluids were used as working fluids in combined systems. Influences of different parameters such as evaporator, condenser, boiler temperatures, and turbine and compressor isentropic efficiencies on COPsys and ηex,sys were analyzed. Second law efficiency, degree of thermodynamic perfection, exergy destruction rate, and exergy destruction ratio were detected for each component in systems. R600a was determined as the most efficient working fluid for proposed systems. Both COPsys and ηex,sys of combined ORC-single evaporator VCR cycle was detected to be higher than the system with dual evaporator. [ABSTRACT FROM AUTHOR]

This study explores the implementation of two large micro-channel heat exchangers as evaporators in a refrigeration cycle intended for thermal management onboard future space vehicles. Examined are thermal performances of the two heat exchangers, thermodynamic performance of the refrigeration cycle, and system instabilities. Because of quality differences, different two-phase flow patterns and dryout effects are encountered in the two heat exchangers. A trade-off exists between optimum performances of the evaporators and compressor, with former favoring outlet quality values below unity to guard against dryout, and the compressor favoring a quality equal to or exceeding unity to preclude internal damage to the compressor from entrained droplets. Thermodynamic analysis of the refrigeration cycle shows exergy destruction is minimum when the avionics HX’s outlet quality is close to unity. The system is shown to be susceptible to instability resulting from interactions between compressible volumes both upstream and downstream of the condenser, and inertia of liquid in the condenser. This instability is manifest by pressure oscillations that are sensitive to both flow rate and evaporator heat input. [ABSTRACT FROM AUTHOR]

The use of efficient refrigerator/freezers helps considerably to reduce the amount of the emitted greenhouse gas. A two-circuit refrigerator-freezer cycle (RF) reveals a higher energy saving potential than a conventional cycle with a single loop of serial evaporators, owing to pressure drop in each evaporator during refrigeration operation and low compression ratio. Therefore, several industrial applications and fish storage systems have been utilized by using multipurpose refrigeration cycle. That is why a theoretical performance analysis based on the exergetic performance coefficient, coefficient of performance (COP), exergy efficiency and exergy destruction ratio criteria, has been carried out for a multipurpose refrigeration system by using different refrigerants in serial and parallel operation conditions. The exergetic performance coefficient criterion is defined as the ratio of exergy output to the total exergy destruction rate (or loss rate of availability). According to the results of the study, the refrigerant R32 shows the best performance in terms of exergetic performance coefficient, COP, exergy efficiency, and exergy destruction ratio from among the other refrigerants (R1234yf, R1234ze, R404A, R407C, R410A, R143A and R502). The effects of the condenser, freezer-evaporator and refrigerator-evaporator temperatures on the exergetic performance coefficient, COP, exergy efficiency and exergy destruction ratios have been fully analyzed for the refrigerant R32. [ABSTRACT FROM AUTHOR]

In this study, the performance of a novel photovoltaic/thermal (PV/T) air dual-heat-source composite heat pump hot water system was investigated experimentally and analyzed theoretically. First, a system that simulates a solar PV/T collector by electric heating was built and tested to validate the superiority of the hot water system. The system was divided into dual-heat-source operating mode and single-heat-source operating mode. Results showed that the average COP and COP sys for dual-heat-source operating mode were 2.49 and 2.24, respectively, and for single-heat-source operating mode were 1.40 and 1.31, respectively, which indicate that the former had better system performance. Then, the actual PV/T collector was used in the system. The results showed that the average electrical gain and heat gain were 278 W and 664 W, respectively. The average electrical efficiency and heat efficiency were 14.5% and 36.02%, respectively. Meanwhile, the comprehensive efficiency was more than 50%. The average COP and COP sys of the heat pump were 4.08 and 3.07, respectively, along with the system exergy efficiency of 0.33. Therefore, the PV/T air dual-heat-source composite heat pump hot water system has excellent performance and is worth promoting and applying. [ABSTRACT FROM AUTHOR]

Highlights: [•] A full factorial analysis is conducted upon a triple absorption heat transformer. [•] The most influential variable settings are determined. [•] Condensation temperature and pinch heat transfer gradient have the greatest influence. [•] Points of optimum exist for the temperatures of the two absorber evaporators. [•] The generator causes the most irreversibility. [ABSTRACT FROM AUTHOR]