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[en] This paper describes a theoretical analysis of a heat-powered refrigeration cycle, a combined Rankine-vapour-compression refrigeration cycle. This refrigeration cycle combines an Organic Rankine Cycle and a vapour-compression cycle. The cycle can be powered by low grade thermal energy as low as 60 deg. C and can produce cooling temperature as low as -10 deg. C. In the analysis, two combined Rankine-vapour-compression refrigeration cycles were investigated: the system with R22 and the system with R134a. Calculated COP values between 0.1 and 0.6 of both the systems were found.
[en] A dynamic simulation of a photovoltaic vapour compression system is presented in this paper. In particular, there are several options to convert solar energy into refrigeration effect such as the absorption cycle, the thermo-mechanical refrigeration systems, the regenerative desiccant process or the steam jet system. This effect can also be produced by a conventional vapor compression cycle in which the compressor is driven by an electric motor supplied by means of photovoltaic cells. It is also possible to produce the cooling effect adopting the thermoelectric refrigeration, with electricity supplied by means of photovoltaic cells. Absorption and solar mechanical systems are necessarily larger and require extensive plumbing and electrical connections. The dynamic model allows to obtain some characteristic temperatures of the photovoltaic system and the energy consumptions with and without load perturbations. This model results a useful tool to study the dynamic working, for example, of photovoltaic refrigerators used in rural areas and remote islands, for their simple structure and low costs, to preserve foodstuffs, vaccines and other life saving medicines. (author)
[en] This paper presents several correlation based models to be used for estimation of the energy performance of vapor compression screw chillers. They were developed using a detail thermodynamic model, contained in the ASHRAE Toolkit-I, for (1) identification of chiller parameters along with data from the manufacturer's catalogue and (2) simulation of the energy performance of screw chillers. The new models were compared with those currently used for centrifugal chillers. The energy performance of screw chillers from two different manufacturers was also compared
[en] An exergetic analysis of a centralized system of air conditioning, based on a vapor compression refrigeration cycle, appears in this article. The investigation allows to calculate the irreversibilities (exergy destruction) in the main components of the refrigeration cycle as well as to evaluate the sensitivity of this indicator when the operating conditions changes. As main result the most sensible components of the cycle are identified, information that will be useful in order to define strategies of operation focused to the power efficiency increase.
[en] Highlights: • A hybrid ejector-vapor compression cycle (EVCC) was proposed by using R134a. • The EVCC comprises of a vapor compression and ejector refrigeration sub-cycles. • The range of optimal NXPs for higher ARs is narrower and vice versa for lower ARs. • Conditions for higher COPs of the VCSC and COP improvements were obtained. • On average, the COP improvement of the EVCC over the VCSC reaches at 19.4%. - Abstract: Improving the Coefficient of Performance (COP) of the vapor compression refrigeration cycle (VCRC) is one of the primary objectives in the HVAC&R field. In this paper, a hybrid ejector-vapor compression cycle (EVCC) was presented to improve the COP of the vapor compression sub-cycle (VCSC). That is to say, the sub-cooling degree of the VCSC was improved by using the cooling effect of the ejector refrigeration sub-cycle (ERSC). R134a was employed in both sub-cycles. Specific experimental studies conducted were: (1) seeking the relations between the optimal nozzle exit positions and area ratio of the ejector to improve the performance of the ERSC, (2) investigating the influence of the compressor frequency on the capability of the VCSC, and (3) evaluating the effect of the compressor frequency as well as the evaporation temperature of the ERSC on the characteristics of the EVCC. As a result, two significant findings were obtained: (1) the range of optimal NXPs for higher ARs is quite narrow and vice versa for lower ARs, (2) on average, the COP improvement of the EVCC over the VCSC reaches 19.4%.
[en] Highlights: • An ejector was used as an expander for reducing throttling losses. • Experiments were made under the same external conditions and cooling capacities. • Work recovery in the ejector was achieved about 39–42%. • The exergy efficiency of the R134a cycle was improved by 6.6–11.24%. - Abstract: An experimental study was conducted on vapor compression refrigerators using R134a refrigerant for the purpose of achieving energy recovery and decreasing the effects of irreversibility. An ejector was used as an expander instead of an expansion valve. The coefficient of performance of the ejector refrigeration system and the amount of irreversibility and efficiency of each of its components were determined and compared with those of a basic vapor compression refrigeration system of the same cooling capacity under the same external conditions. It was found that the ejector expander system exhibited a lower total irreversibility in comparison with the basic system. When the ejector was used as the expander in the refrigeration system, the coefficient of performance was higher than in the basic system by 7.34–12.87%, while the exergy efficiency values were 6.6–11.24% higher than in the basic system
[en] The purpose of this paper is to present exergy charts for carbon dioxide (CO2) based on the new fundamental equation of state and the results of a thermodynamic analysis of conventional and trans-critical vapour compression refrigeration cycles using the data thereof. The calculation scheme is anchored on the Mathematica platform. There exist upper and lower bounds for the high cycle pressure for a given set of evaporating and pre-throttling temperatures. The maximum possible exergetic efficiency for each case was determined. Empirical correlations for exergetic efficiency and COP, valid in the range of temperatures studied here, are obtained. The exergy losses have been quantified
[en] Submitted by nuclear-physical methods of determining the coefficient of absorption of iodine carbon materials using stable isotopes of iodine. Designed and created by pumping and measuring iodine content units. The processes of dynamic sorption of iodine on industrial carbon adsorbents studied the possibility of determining the iodine content of nuclear-physical methods and presents the metrological characteristics x-ray method. Application methods allow for the certification of carbon adsorbents gas cleaning systems and improve the safety of nuclear power plant operation
[en] The performance of an air to water vapor compression heat pump has been investigated experimentally. The main purpose of this study was to investigate the possibilities of using R134a as a working fluid to replace R22 for vapor compression heat pumps. Pure R22, pure R134a and some binary mixtures of R22/R134a were considered as working fluids. The performance of the system was characterized by mixture ratio, COP and evaporator air inlet temperature. Comparisons are made between the pure refrigerants and refrigerant mixtures on the basis of the COP. Experimental results show that the mixture ratio affects the COP significantly, and the COP could be improved by using pure R134a or an appropriate mixture of R134a/R22 instead of pure R22. The maximum COP occurred at a mixture ratio of around 50/50% R134a/R22. For a mass percentage of 50% of R134a, the COP was enhanced by about average 25%
[en] Highlights: • A novel dual-nozzle ejector enhanced refrigeration cycle is proposed. • The novel cycle is evaluated by using the developed mathematical model. • The results show the performances of the novel cycle could be significantly improved. • The novel cycle shows its promise in household refrigerator-freezers applications. - Abstract: In this study, a novel dual-nozzle ejector enhanced refrigeration cycle is presented for dual evaporator household refrigerator-freezers. The proposed ejector equipped with two nozzles can efficiently recover the expansion work from cycle throttling processes and enhance cycle performances. The performances of the novel cycle are evaluated by using the developed mathematical model, and then compared with that of the conventional ejector enhanced refrigeration cycle and basic vapor-compression refrigeration cycle. The simulation results show that for the given operating conditions, the coefficient of performance (COP) of the novel cycle using refrigerant R134a is improved by 22.9–50.8% compared with that of the basic vapor-compression refrigeration cycle, and the COP improvement is 10.5–30.8% larger than that of the conventional ejector enhanced refrigeration cycle. The further simulation results of the novel cycle using refrigerant R600a indicate that the cycle COP and volumetric refrigeration capacity could be significantly improved