查看更多>>摘要：This study proposed a two-stage cascade organic Rankine cycle (ORC) to harvest the medium and low-temperature discharged heat from internal combustion engine (ICE), and a liquefied natural gas (LNG) cold energy system is integrated into the proposed cycle in order to realize the cascade utilization of ICE multi-grade waste heat more efficiently. The thermodynamic and economic models are developed to investigate the proposed system performance under steady-state conditions. The influence of the important thermodynamic parameters, e.g. the ORC turbine inlet temperature, the high pressure of first-stage ORC and the outlet temperature of condenser are investigated. The calculated results indicated that the thermal efficiency and the exergy efficiency achieved 27.31% and 33.73%, respectively. In addition, it was found that the total sum unit cost of system product was decreased by increasing turbine Ⅰ inlet pressure. Furthermore, to reach the conflicting compromise between the two aspects of thermodynamic and economic, the Non-dominated Sorting Genetic Algorithm (NSGA-II) is employed to carry out the multi-objective optimization study by which the external investment cost and the thermal efficiency are selected as the objective function. At the same time, the influence region of decision variables related to the optimization is determined according to the scatter distribution of decision variables. Moreover, the exergy destruction and the investment cost ratio of each component under the optimization conditions are analyzed to obtain the preferred performance of the key components. The findings could provide references for the ORC system design and operation driven by multi-grade waste heat.
查看更多>>摘要：Current alternatives to R404A are either refrigerants with higher global warming potentials (GWP) from 1200 to 2000 or mildly flammable refrigerants with a charge limit of 1.2 kg. Therefore, nonflammable alternatives to R404A with lower GWP values need to be developed. In this study, a new non-flammable refrigerant blend, named RTJU-Z (GWP of 794), has been proposed to directly replace R404A in a cold storage system with no modification. The flammability and thermodynamic performance of RTJU-Z were studied experimentally. The results show that RTJU-Z couldn't be ignited successfully and had a higher coefficient of performance (COP) value than that of R404A by 2.15%-5.71% at different cold storage temperatures. The optimal charge of RTJU-Z for the experimental system was 11.76% lower than that of R404A. The refrigeration capacity of RTJU-Z was about the same as that of R404A at the cold storage temperature from -20 °C to 10 °C. It is concluded that RTJU-Z can be directly used as a non-flammable alternative to R404A in a cold storage system with no modification.
查看更多>>摘要：The ambient condition varies drastically in the composite climate and the direct evaporative cooling is effective in the dry months; whereas, the regenerative evaporative cooling is effective in the humid months. Hence, seasonal change of the cooling device is needed for effective cooling. In this situation, a dual-mode evaporative cooler (a two-in-one device) is an intelligent choice, which operates in direct mode in the dry months and regenerative mode in the humid months. Hence, this novel evaporative cooler is fabricated in this study and experimental exergy, economic, and sustainability analyses are performed to check the acceptability. Effects of various operating parameters on the performance are experimented in both (indirect and direct) modes of operation. The exergy destruction, exergy efficiency, sustainability index, and specific total cost of the developed device are estimated in both modes of operation. It is found that the exergy efficiency and sustainability index of the regenerative mode are higher while the specific total cost of the direct mode is lower. The developed device is more economical in both operating modes as compared to the conventional air conditioner.
查看更多>>摘要：The paper based on the solid adsorption vacuum flash ice slurry production device, the process of distilled water flashing was recorded with a high-speed CCD camera, and the vacuum flashing state of distilled water at different pressures and different initial temperatures was analyzed by experimental phenomena. The effect of system pressure, different wall temperatures and solution volumes on the subcooling state of the ice slurry formation process under solid adsorption vacuum flash evaporation was also experimentally investigated. The results show that the lower the pressure the more intense the flashing phenomenon in the vacuum flashing state, and the higher the initial temperature the more likely the solution is to produce bubbles. Within 20 seconds after the start of the experiment, distilled water will appear subcooling phenomenon in solid adsorption vacuum flash evaporation ice making system, due to the vacuum flash action water is constantly disturbed subcooling state duration is very short. The lower the pressure, the lower the subcooling degree, the subcooling degree is about 2 °C - 4 °C. The wall temperature has a greater impact on the ice crystal phase change accumulation stage, the higher the initial wall temperature the greater the fluctuations in the subsequent stages of flashing and the lower the ice content. When the volume of the solution is small, the liquid film is prone to flash formation of solid ice.
查看更多>>摘要：This paper discusses the results of an experimental analysis of the use of R450A and R513A as drop-in alternatives to R134a in a water-to-water heat pump. The heat pump is tested setting the rotational frequency of the compressor shaft, the vapour superheating at the evaporator outlet and the mass flow rates and temperatures of the secondary fluids at the heat exchangers outlets to the desired conditions. Compared to R134a, the use of R450A leads to a capacity reduction, that lays in the range 6.59% to 15.02%, and to a COP variation, that is within the range ?2.48% to +2.99%, whereas with R513A the variations of the heating capacity and COP lay in the range ?8.78% to +3.16% and ?7.48% to +2.22% respectively. The increase in the rotational frequency of the compressor shaft to bring the heating capacity back to the R134a values is discussed too. The required increase is in the range 10% to 16% with R450A and 2% to 8% with R513A, but a COP reduction in the range 0.14% to 5.22% with the former refrigerant and 2.34% to 6.48% with the latter consequently arises.
查看更多>>摘要：R1132(E) (trans-1,2-difluoroethylene, C2H2F2) is a potential next generation refrigerant to be utilized in air conditioning applications. This hydrofluoroolefin (HFO) refrigerant possesses an extremely low-GWP value below 1 and it is an excellent candidate for replacing R32 in blends such as R410A, which are subjected to local and international greenhouse gas regulations for limiting global warming. Two isochoric apparatus were used to measure the saturation pressures of R1132(E) from 240 K to its critical temperature. At the critical temperature, the critical pressure of R1132(E) was also directly measured. Twenty-four saturation pressures including the critical point were used for optimizing a Wagner-type equation representing the saturation pressure curve. The absolute average deviation of the saturation pressures of R1132(E) predicted by the model using the fitted parameters and the experimental data is 0.02%. The optimized Wagner-type equation of saturation pressures is used for determining the acentric factor of R1132(E) as 0.2433, which is further utilized for the prediction of the saturation pressures using the Peng-Robinson cubic equation of state within an absolute average deviation of 0.31%.
查看更多>>摘要：Many researchers have carried out study on refrigerant charge fault for variable refrigerant flow (VRF) air-conditioning system, while few pay attention to refrigerant charge fault for vapor-compression refrigerant cycle system (VCS) of enhanced vapor injection (EVI) with a flash tank onboard. To develop a strategy for refrigerant charge fault of the above system, the optimization methods have been implemented to predict the refrigerant charge level (RCL) based on virtual refrigerant charge (VRC) models. Firstly, Pearson correlation coefficient analysis is employed to obtain the characteristic parameters. Secondly, a piecewise modified VRC model with the different characteristic parameters from VRC models is obtained for two cases of RCL < 75% and RCL > 75%. Meanwhile, combined with the principal component analysis (PCA) and the support vector machine (SVM) algorithm, a PCA-SVM model is developed to improve the prediction accuracy, and the average root mean squared error (RMSE) is only 7.8 compared to 14.9 of the modified VRC model when RCL > 75%, meanwhile, the correctly detected ratio is improved from 62.8% to 84.5%. Then, for solving the difficulty of fault detection and diagnosis (FDD) when RCL > 160%, the moving time window average (MA) algorithm is introduced and an online PCA-MA-SVM model is developed. Finally, a hybrid piecewise FDD strategy combined with three models for refrigeration charge fault in airborne VCS of EVI with a flash tank is obtained.
查看更多>>摘要：Passive cooling is a promising way to remove the decay heat and ensure the security of Spent Fuel Pool (SFP) at emergency conditions. A potential scheme of the passive cooling system consisting of bundles of large separate heat pipes is presented. A numerical model of the heat pipe is established. The model considered the pool boiling effect in the evaporator and self-adjusting of liquid column height in the downcomer. Influences of evaporator outlet vapor quality and corresponding flow resistance are studied. The model shows reasonable agreement with experimental data. Thermal performance and flow features with different working fluids, namely ammonia, water and R134a, under various conditions are analyzed. It is found that there is a minimum condenser height to activate the passive cooling system. Elevate the condenser helps to enhance the system performance when the downcomer is fully liquid filled. But when the downcomer is partially liquid filled, elevation of condenser provides little benefit. Besides, the cooling system functions well in a wide filling ratio range. Increase of filling ratio leads to growth of liquid column height in the downcomer. When the liquid column height comes to the maximum value, the cooling system shows the best heat transfer performance. In long distance heat transport applications, cooling system with water as the working fluid performs poorly. To balance between security and thermal performance, R134a is a better choice for the SFP passive cooling system than ammonia and water.
NSTL
Elsevier