查看更多>>摘要：In this study, a multi evaporator vapor-compression refrigeration (mVCR) system driven by Organic Rankine Cycle (ORC) is proposed as a refrigeration system for supermarkets, restaurants, etc. The system is analyzed for its thermodynamic performance in terms of coefficient of performance (COPs) and exergetic efficiency (ηex). A zeotropic mixture of hexane and R245fa is used as working fluid over pure fluid to assess its impact on the thermodynamic performance of the system. Moreover, the system is optimized using an evolutionary algorithm called genetic algorithm (GA) to determine the optimal values of the operating parameters for the maximum exergetic efficiency of the system. The results indicate that COPs and ηex are maximum at the mass fraction of 0.5 of the zeotropic mixture. The maximum values of COPs and ηex are 0.425 and 31.1% respectively. The system can achieve an exergetic efficiency of 58% at the optimal set of operating parameters. The corresponding optimal values of the temperature of the ORC evaporator, VCR evaporator 1, VCR evaporator 2, and the condenser are 388 K, 268 K, 268 K, and 303 K respectively.
查看更多>>摘要：This communication develops a novel cooling-power cogeneration system consisting of a parabolic trough collector utilizes gasses as the medium for solar to heat conversion, and the Kalina cycle integrated series-flow double effect LiBr-H2O absorption chiller to generate electricity and large cooling, simultaneously. By developing a thermal model, a simulation through EES is conducted to investigate the influence of internal tube diameter of absorber and solar irradiation on the exit temperature of SHTF and flowing mass of the working fluid of Kalina cycle. It is determined that for the given inlet temperature and solar irradiation, the outlet temperature of SHTF is declined when the internal diameter of absorber tube is increased. The effect of change in SHTF, pressure at expander entry, and the concentration of ammonia-water basic solution on electrical power produced, refrigeration capacity, exergy of refrigeration, efficiencies of the cogeneration cycle are investigated. The cogeneration cycle with helium operated PTSC indicates better results than the use of air and CO2 as SHTF. Increase in the outlet temperature of SHTF (helium) leads to considerable increase in electrical power, refrigeration capacity, and exergy of refrigeration. The breaking down of solar exergy supplied to developed configuration reveals an exergy destruction of the order of 64.01% along with the exergy loss to environment of 1.92%, and exergy of refrigeration of 4.65% with generated power exergy of 29.42%, respectively. The computational results of present investigation are compared with the theoretically published data and a good agreement is found between these data.
查看更多>>摘要：Temperature-time (T-T) defrosting control strategy is widely used in traditional air-source heat pump (ASHP) units. Its fatal problem that urgently need to be addressed is mal-defrosting, which happens frequently in heating season and causes extra energy loss. In order to accurately control the defrosting time and avoid the mal-defrosting problem, a novel Temperature-Humidity-Image (T-H-I) defrosting control strategy is proposed to improve the defrosting process. With the aid of image processing technology, T-H-I defrosting control strategy applies fractal analysis can accurately and effectively perform defrosting operation. Through the experimental investigation on frost formation characteristics, T-H-I defrosting control strategy operates defrosting when the frost thickness reaches 0.726 mm and the fractal dimension reaches 2.839, while it terminates when the fractal dimension decreases to 2.324. Comparative experiments of ASHP unit with traditional temperature-time (T-T) method and the proposed T-H-I method are conducted. Compared with the traditional T-T method, 'delayed defrosting' and 'unnecessary defrosting' are avoided effectively with the T-H-I defrosting control strategy, and the energy consumption of defrosting can be reduced by 10.6% and 22.3%, respectively. In view of its high accuracy in defrosting and effectiveness in energy saving, the proposed T-H-I method has a promising prospect for future application.
NSTL
Elsevier