In this paper,an ejector enhanced high-temperature heat pump with dual-pressure condensation and evaporation is proposed to improve the system performance.Theoretical analyses of the system operation characteristics are conducted using energetic and exergetic methods.The performance comparisons among the basic cycle,parallel compression cycle,and ejector enhanced cycle are conducted with six different refrigerants,including R245fa,R600a,R1234ze(Z),R1336mzz(Z),R1224yd(Z),and R1233zd(E).The results demonstrate that environmentally-friendly refrigerant R1234ze(Z)would be a promising alternative refrigerant.Compared with the basic cycle and parallel compression cycle at selected operation conditions,29.5%and 12.6%improvements in COP,and 16.7%and 11.1%higher system exergy efficiency are achieved in the ejector enhanced cycle on average.The volumetric heating capacity of the ejector enhanced cycle is increased by 15.7%–21.7%.The ejector enhanced cycle outperforms the other two cycles in high-temperature heat pump applications at the large temperature lift and temperature rise in the heat sink.The assessment offers an option to improve the energy utilization efficiency of the high-temperature heat pumps.
Elastocaloric cooling is regarded as one of the most promising cutting-edge alternatives to conventional vapor compression refrigeration systems.This technology is based on the temperature change of materials when being subjected to uniaxial stress,which has been observed in polymers,alloys,and ceramics.However,the existing elastocaloric prototypes have a bottleneck problem of an excessive mass ratio between the actuator and the solid-state refrigerant.
Antibacterial materials play an important role in clinical application, and silver has been known to exhibit strong cytotoxicity towards a broad range of micro-organisms. In this work, the amorphous calcium phosphate with silver substitution （Ag-ACP） was synthesized by chemical precipitation method, and the valence of silver in ACP was adjusted by temperature. The processed Ag-ACP was combined with slightly acidic compounds to form new calcium phosphate cement （CPC）. Our results indicate that the valence of silver in CPC was adjusted successfully by chemical precipitation method and heat treatment. X-ray diffraction （XRD） and X-ray photoelectron spectroscopy （XPS） results demonstrated that silver ion in CPC-1 and CPC-2 existed in Ag3PO4, after heat treatment of 460℃, silver became more stable in CPC-3 and CPC-4. Silver in CPC-1 end CPC-2 exhibited better releasing property. After heat treatment at 460 ℃, the amount of silver ion released from CPC decreased significantly. Besides, the antibacterial ability of Ag-CPC was adjusted by changing the valence of silver in Ag-CPC. Depending on the low valence of silver and good silver release, CPC-1 and CPC-2 exhibited better antibacterial activity. We believe that this study will motivate the development and applications of antibacterial CPC in bone tissue regeneration.
In this paper,an ejector enhanced two-stage auto-cascade refrigeration cycle(EARC)using ternary mixture R600a/R32/R1150 is proposed for application of-80℃freezing.In EARC cycle,an ejector was employed to recover the expansion work in the throttling processes and lifted the suction pressure of the compressor.The performances of the ejector enhanced two-stage auto-cascade refrigeration cycle and conventional auto-cascade refrigeration cycle(CARC)were compared using thermodynamic analysis methods.The influences of the important operation parameters including mass fraction ratio of the mixture,fluid quality at the second separator inlet,condensation temperature,evaporation temperature,and expansion ratio of expansion valve on the performances of EARC cycle were discussed in detail.The results indicate that ternary mixture R600a/R32/R1150 has the optimal mass fraction ratio of 0.45/0.2/0.35 with respect to the maximum COP.The EARC cycle yields higher performance than the CARC cycle in terms of COP,exergy efficiency and volumetric refrigeration capacity.And 4.9%-36.5%improvement in COP and 6.9%-34.3%higher exergy efficiency could be obtained in EARC cycle comparing with CARC cycle.The finding of this study suggests that the EARC cycle has a promising application potential for low temperature freezing.
