Superelastic martensitic transformation(MT)confers a considerable elastocaloric response to shape memory alloys,but the significant hysteretic loss cripples the energy conversion efficiency.In the present work,large e...Superelastic martensitic transformation(MT)confers a considerable elastocaloric response to shape memory alloys,but the significant hysteretic loss cripples the energy conversion efficiency.In the present work,large elastocaloric effect with high refrigeration efficiency is realized in a polycrystalline Co_(50)V_(35)Ga_(15)Heusler alloy.Experimental results show that the studied alloy undergoes a paramagnetic type MT from L2_(1)cubic austenite to D0_(22)tetragonal martensite with a small thermal hysteresis(ΔT_(hys))of~3 K.By carefully examining the strain rate dependence of superelastic response,it is also found that the stress hysteresis(Δσ_(hys))consists of two components including intrinsic stress hysteresis(Δσ_(hys)^(int.))caused by inherent attribute of MT and extrinsic stress hysteresis(Δσ_(hys)^(ext.))aroused by applied strain rate.Accordingly,we put forward a strain relaxation equation to separate the relative contributions betweenΔσ_(hys)^(int.)andΔσ_(hys)^(ext.)quantitatively,which demonstrates that a smallΔT_(hys)is conducive to substantial decrease inΔσ_(hys)^(int.).Moreover,associated with stress-induced superelastic MT,large reversible adiabatic temperature changes(ΔT_(ad))higher than 11 K are achieved under an applied strain of 6.5%over a temperature range of at least 60 K.With the combination of a large elastocaloric cooling capacity and a low energy dissipation,significant improvements in refrigeration efficiency can be obtained in a wide strain range,being superior to those reported in most of typical elastocaloric materials near room temperature.展开更多
The helium turbine expander,a pivotal component within a hydrogen liquefaction system,is crucial for effective cooling.Through the use of a multistage series-connected turbine expander,the system is able to accommodat...The helium turbine expander,a pivotal component within a hydrogen liquefaction system,is crucial for effective cooling.Through the use of a multistage series-connected turbine expander,the system is able to accommodate more complex operating conditions and provide enhanced refrigeration efficiency by a gradual and controlled reduction in temperature,thereby optimizing overall performance.In this study,the interstage characteristics of a two-stage series-connected helium turbine expander in a hydrogen liquefaction system employing the inverse Brayton cycle are analyzed in depth.After validation of the reliability of the numerical simulation results using a rigorous on-site joint test system incorporating the helium turbine expander,the operational performance of each expander stage and that of the second-stage expander under various operating conditions are obtained.In addition,the energy loss distributions within various through-flow components and the primary loss zones within the impeller are comprehensively analyzed on the basis of entropy production theory.The findings presented in this paper represent a significant contribution in providing a foundational reference for the development of multistage series-connected cryogenic gas turbine expanders.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52261035,52201223,52371006,52371194)Applied Basic Projects of Yunnan province(No.202101BA070001-233).
文摘Superelastic martensitic transformation(MT)confers a considerable elastocaloric response to shape memory alloys,but the significant hysteretic loss cripples the energy conversion efficiency.In the present work,large elastocaloric effect with high refrigeration efficiency is realized in a polycrystalline Co_(50)V_(35)Ga_(15)Heusler alloy.Experimental results show that the studied alloy undergoes a paramagnetic type MT from L2_(1)cubic austenite to D0_(22)tetragonal martensite with a small thermal hysteresis(ΔT_(hys))of~3 K.By carefully examining the strain rate dependence of superelastic response,it is also found that the stress hysteresis(Δσ_(hys))consists of two components including intrinsic stress hysteresis(Δσ_(hys)^(int.))caused by inherent attribute of MT and extrinsic stress hysteresis(Δσ_(hys)^(ext.))aroused by applied strain rate.Accordingly,we put forward a strain relaxation equation to separate the relative contributions betweenΔσ_(hys)^(int.)andΔσ_(hys)^(ext.)quantitatively,which demonstrates that a smallΔT_(hys)is conducive to substantial decrease inΔσ_(hys)^(int.).Moreover,associated with stress-induced superelastic MT,large reversible adiabatic temperature changes(ΔT_(ad))higher than 11 K are achieved under an applied strain of 6.5%over a temperature range of at least 60 K.With the combination of a large elastocaloric cooling capacity and a low energy dissipation,significant improvements in refrigeration efficiency can be obtained in a wide strain range,being superior to those reported in most of typical elastocaloric materials near room temperature.
基金supported by the Zhejiang Provincial Key Research and Development Project No.2023C03158.
文摘The helium turbine expander,a pivotal component within a hydrogen liquefaction system,is crucial for effective cooling.Through the use of a multistage series-connected turbine expander,the system is able to accommodate more complex operating conditions and provide enhanced refrigeration efficiency by a gradual and controlled reduction in temperature,thereby optimizing overall performance.In this study,the interstage characteristics of a two-stage series-connected helium turbine expander in a hydrogen liquefaction system employing the inverse Brayton cycle are analyzed in depth.After validation of the reliability of the numerical simulation results using a rigorous on-site joint test system incorporating the helium turbine expander,the operational performance of each expander stage and that of the second-stage expander under various operating conditions are obtained.In addition,the energy loss distributions within various through-flow components and the primary loss zones within the impeller are comprehensively analyzed on the basis of entropy production theory.The findings presented in this paper represent a significant contribution in providing a foundational reference for the development of multistage series-connected cryogenic gas turbine expanders.
