In this paper, an advanced ejector-expansion autocascade refrigeration cycle (AEARC) using hydrocarbon mixture R290/R170 for applications in low-temperature freezers is proposed. In the AEARC, a ...two-phase flow driven ejector is introduced with new cycle configuration to reduce the thermodynamic loss in throttling process and lift the suction pressure of compressor significantly. The performances of the AEARC and traditional autocascade refrigeration cycle (ARC) are compared using energy and exergy analysis methods, and several important parameters for AEARC are also discussed in detail. The results indicate that AEARC is feasible and there are obvious performances improvements in theCOP, volumetric refrigeration capacity and exergic efficiency. Especially, in AEARC, the COP and volumetric refrigeration capacity increase by 80.0% and 78.5% at most compared to that of ARC, respectively. In general, the AEARC can provide significant performance improvement and produce better actual operation benefit. The potential practical advantages may be worth further attention in future research.
•An advanced ejector-expansion autocascade refrigeration cycle is presented.•Energy and exergy analysis are applied.•The performances of the presented cycle are compared with those of the basic cycle.•The presented cycle shows obvious COP, volumetric refrigeration capacity and exergic efficiency improvements.
•A new direct-expansion solar assisted vapor injection heat pump cycle is present.•The performance of the new cycles is investigated by simulation method.•The new cycle obviously outperforms the ...traditional vapor injection heat pump cycle.•The new cycle has two operation modes to be chosen according to the solar radiation.•There is optimum injection pressure for the new cycle to obtain the maximum COP.
A new direct-expansion solar assisted vapor injection heat pump cycle with subcooler for water heater is proposed in this paper which aims to improve the performance of traditional subcooler vapor injection heat pump cycle by utilizing the solar energy. The new cycle has two working modes (SVIC mode and DX-SVIC mode) to be switched according to the solar radiation intensity. The performance enhancement potential of the new cycle is investigated by comparing with the traditional cycle through theoretical method. Under the considered conditions, the new cycle yields an average of 14.6% and 42.9% improvement in the heating coefficient of performance and heating capacity aspects compared with the traditional cycle, respectively. Both the new cycle and the traditional cycle have optimum injection pressures to obtain the maximum heating coefficient of performance. The simulation results indicate that the DX-SVIC mode outperforms the SVIC mode on most solar radiation condition, while the latter one is suitable for the extremely low and no solar radiation condition. The energy performance and heat exergy of the new cycle are improved with enhancing the solar radiation, while the variation of exergy efficiency shows contrary tendency. As increasing the injection pressure, the exergy input decreases more rapidly than the heat exergy, and thus the exergy efficiency is improved. The increase of the solar collector area always leads to the energy performance improvement of the new cycle.
This paper describes a new ejector refrigeration system with mechanical subcooling which uses an auxiliary liquid–gas ejector to enhance subcooling for the refrigerant from condenser. The new system ...can have larger subcooling degree when circulating pump consumes a little more power compared with conventional ejector refrigeration system. Based on the built mathematical model, the performance of the new ejector refrigeration system was discussed and compared with that of a conventional ejector refrigeration system for refrigerant R142b. Theoretical analyzing results show that the new system can efficiently improve the coefficient of performance (COP) of ejector refrigeration.
In this paper, exergy method is applied to analyze the ejector expansion Joule–Thomson (EJT) cryogenic refrigeration cycle. The exergy destruction rate in each component of the EJT cycle is evaluated ...in detail. The effect of some main parameters on the exergy destruction and exergetic efficiency of the cycle is also investigated. The most significant exergy destruction rates in the cycle are in the compressor and ejector. The ejector pressure ratio and compressor isothermal efficiency have a significant effect on the exergetic efficiency of the EJT cycle. The exergy analysis results show the EJT cycle has an obvious increase in the exergetic efficiency compared to the basic Joule–Thomson refrigeration cycle. A significant advantage from the use of the ejector is that the total exergy destruction of the EJT cycle can be reduced due to much more decreasing of the exergy destruction rates in the compressor and expansion valve. The exergy analysis also reconfirms that applying an ejector is a very important approach to improve the performance of the Joule–Thomson cryogenic refrigeration cycle.
In the present study, a novel optimization model is developed based on the available work loss minimization for tube-in-tube helically coiled heat exchangers. The present numerical model takes into ...account available work losses, i.e. irreversibilities, due to heat transfer and frictional pressure drops of heat exchangers. By employing the expression of Carnot cycle efficiency, the formula for calculating the available work loss resulting from the irreversible heat transfer process is obtained and then utilized in the computation of the total available work loss. In the case under study, the effects of main design parameters of the heat exchanger on the available work loss are discussed in detail and the optimal design parameters of the heat exchanger are also obtained under the specified condition. The model and results presented here for the optimization of tube-in-tube helically coiled heat exchangers may provide a helpful guidance for applying such heat exchangers in Joule–Thomson refrigerators.
► An optimization model for tube-in-tube helically coiled heat exchangers is developed. ► The model is based on the available work loss minimization. ► The Carnot cycle efficiency is employed to calculate the available work loss. ► The effects of main design parameters on the available work loss are discussed. ► The optimal design parameters of the studied heat exchanger are obtained.
•The two-phase driven ejector performance was experimentally studied.•Effects of operational and geometric parameters for the ejector were examined.•The ejector performance was strongly affected by ...those parameters.•Maximum ejector efficiency could be obtained with proper parameters.
This paper presents an experimental investigation on two-phase driven ejector performance characteristics in a novel ejector enhanced refrigeration system (NERC). An experimental setup using refrigerant R600a is designed and built based on the NERC system. In the experimental setup, the ejector uses two-phase refrigerant coming from the high-temperature evaporator as the primary fluid. The experiments are carried out to examine the influences of the main operational and geometric parameters, including the primary fluid pressure, the secondary fluid pressure, the NXP and the nozzle throat diameter. The results show that the entrainment ratio, the pressure lift ratio and the overall ejector efficiency of the two-phase driven ejector are strongly affected by those parameters. Additionally, the effect of the quality of the two-phase primary fluid is also experimentally investigated. The meaningful results obtained here may serve as good guidelines for further improving the two-phase driven ejector performance and providing promising use of the two-phase driven ejector in the ejector-expansion technology.
Abstract
Herein, the microstructure, mechanical properties, and fatigue crack growth (FCG) behavior of 51CrV4 spring steels under different quenching and tempering heat treatment were studied. ...Results show that tempering temperature would not affect the prior austenite grain (PAG) size, while quenching temperature has a great influence on it; the volume fraction of carbide precipitates decreased with increasing quenching temperature. The width of martensite lath has little relationship with the prior austenite grain size. The mechanical properties of the investigated steels decreased with an increasing tempering temperature. Tempering temperature had a greater influence on the fatigue crack growth behavior compared with quenching temperature. The FCG of all the investigated steels were well interpreted by Paris model. When the quenching temperature was 840 °C, the stable expanding stage of the fatigue fracture was representative fatigue striations, fatigue steps and secondary cracks; multiple failure mechanisms coexisted in the rapid expanding stage; the fracture morphology of unstable failure stage was mainly dimples. When the quenching temperature increased to 880 °C and 920 °C, quasi-cleavage was observed in all the stages compared with the samples quenched at 840 °C. Secondary cracks, fatigue steps and crack closure could retard the FCG rate by consuming the driving force near the tip of fatigue crack.
In the present study, an optimization model is developed for a thermoelectric cooler (TEC) based on the entropy generation minimization method. In the model, the total entropy generation rate, the ...entropy generation number and the exergetic efficiency are proposed as optimization objective functions, respectively, while the number of transfer units of the heat sink is considered as a constraint. The heat capacity rate of cooling fluid in the heat sink is optimized under other given conditions. The results show that a minimum total entropy generation rate and a minimum entropy generation number can be achieved by optimally selecting the heat capacity rate of the cooling fluid. In addition, the minimum total entropy generation rate and corresponding optimal heat capacity rate of the cooling fluid are both dominated by the number of transfer units and the electrical current. Furthermore, the effects of the heat capacity rate of cooling fluid and the electric current in terms of the exergetic efficiency are also evaluated.
•An optimization model of heat sink configuration for a TEC system is proposed.•An entropy generation minimization method is used to optimize the TEC system.•Number of transfer units of heat sink is considered as a constraint.•Total entropy generation rate is proposed as an optimization objective function.•Optimal heating capacity rate of cooling fluid for heat sink can be obtained.
•An ejector-expansion refrigeration system (ERCS) was experimentally studied.•Effects of ejector geometry parameter (Dt) and charge amount (CA) on ERCS were examined.•The evaporating temperature of ...ERCS was strongly affected by those parameters.•An appropriate refrigerant mass flow rate in the evaporator can be maintained by adjusting CA.
This paper presents an experimental investigation on variations of evaporating temperature (te) with different configuration parameters, including the nozzle throat diameter of ejector (Dt) and the capillary tube length (Lc), in an ejector-expansion refrigeration cycle (ERC) system. In addition, effects of refrigerant charge amount (CA) have been investigated at the different Dt and Lc based on the ERC system. The results show that a reasonable matching between CA and Dt or between CA and Lc can adjust the te while maintaining the mass flow rate of the fluid through the evaporator within an appropriate range. Furthermore, the effects of Dt and Lc on the ejector performances at the different CA have been studied. The results show that the performances of ejector are strongly affected by these parameters. The meaningful results obtained here may serve as good guidelines for developing the ejector expansion refrigeration technologies applied in practical refrigeration systems.
This paper presented a novel autocascade refrigeration cycle (NARC) with an ejector. In the NARC, the ejector is used to recover some available work to increase the compressor suction pressure. The ...NARC enables the compressor to operate at lower pressure ratio, which in turn improves the cycle performance. Theoretical computation model based on the constant pressure-mixing model for the ejector is used to perform a thermodynamic cycle analysis for the NARC with the refrigerant mixture of R23/R134a. The effects of some main parameters on cycle performance were investigated. The results show the NARC has an outstanding merit in decreasing the pressure ratio of compressor as well as increasing the COP. For NARC operated at the condenser outlet temperature of 40
°C, the evaporator inlet temperature of −40.3
°C, and the mass fraction of R23 is 0.15, the pressure ratio of the ejector reaches to 1.35, the pressure ratio of compressor is reduced by 25.8% and the COP is improved by 19.1% over the conventional autocascade refrigeration cycle.
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