This paper investigates the MED(Minimum Entransy Dissipation)optimization of heat transfer processes with the generalized heat transfer law q∝(A(T^(n))m.For the fixed amount of heat transfer,the optimal temperature p...This paper investigates the MED(Minimum Entransy Dissipation)optimization of heat transfer processes with the generalized heat transfer law q∝(A(T^(n))m.For the fixed amount of heat transfer,the optimal temperature paths for the MED are obtained The results show that the strategy of the MED with generalized convective law q∝(△T)^m is that the temperature difference keeps constant,which is in accordance with the famous temperature-difference-field uniformity principle,while the strategy of the MED with linear phenomenological law q∝A(T^-1)is that the temperature ratio keeps constant.For special cases with Dulong-Petit law q∝(△T)^1.25 and an imaginary complex law q∝(△(T^4))^1.25,numerical examples are provided and further compared with the strategies of the MEG(Minimum Entropy Generation),CHF(Constant Heat Flux)and CRT(Constant Reservoir Temperature)operations.Besides,influences of the change of the heat transfer amount on the optimization results with various heat resistance models are discussed in detail.展开更多
With the aim of developing a high-temperature heat pump with a large temperature lift,a novel auto-cascade heat pump using low global warming potential(GWP)refrigerant is proposed.Owing to the large exergy destruction...With the aim of developing a high-temperature heat pump with a large temperature lift,a novel auto-cascade heat pump using low global warming potential(GWP)refrigerant is proposed.Owing to the large exergy destruction between the refrigerant and heat sink with limited heat capacity,a cascade heating approach for obtaining high-temperature water is employed.A zeotropic refrigerant with temperature glide characteristics is selected as the working fluid.The modified heat exchange process reduces the temperature difference during heat transfer,thereby decreasing exergy destruction.A thermodynamic analysis model is established to assess the performance of the proposed autocascade heat pump cycle.The energy and exergy performances of the novel cycle are evaluated and compared with those of the basic cycle.Within the range of water outlet temperature considered here,the heating coefficient of performance and capacity increase by 51.1%and 50.6%,respectively.The proposed cycle decreases the mass flow rate of the refrigerant by 38.7%on average.For evaporating temperatures in the range 10-15℃,the proposed cycle improves the heating coefficient of performance and capacity by 54.7%and 43.9%over the basic cycle.The exergy analysis indicates that excellent exergy performance mainly benefits from the reductions in irreversible destruction between refrigerant and water heat exchange.Overall,the thermodynamic analysis reveals the improvements achieved with the novel auto-cascade heat pump cycle.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51576207,51356001&51579244)
文摘This paper investigates the MED(Minimum Entransy Dissipation)optimization of heat transfer processes with the generalized heat transfer law q∝(A(T^(n))m.For the fixed amount of heat transfer,the optimal temperature paths for the MED are obtained The results show that the strategy of the MED with generalized convective law q∝(△T)^m is that the temperature difference keeps constant,which is in accordance with the famous temperature-difference-field uniformity principle,while the strategy of the MED with linear phenomenological law q∝A(T^-1)is that the temperature ratio keeps constant.For special cases with Dulong-Petit law q∝(△T)^1.25 and an imaginary complex law q∝(△(T^4))^1.25,numerical examples are provided and further compared with the strategies of the MEG(Minimum Entropy Generation),CHF(Constant Heat Flux)and CRT(Constant Reservoir Temperature)operations.Besides,influences of the change of the heat transfer amount on the optimization results with various heat resistance models are discussed in detail.
基金supported by the National Natural Science Foundation of China(NSFC)under Grant No.52076160。
文摘With the aim of developing a high-temperature heat pump with a large temperature lift,a novel auto-cascade heat pump using low global warming potential(GWP)refrigerant is proposed.Owing to the large exergy destruction between the refrigerant and heat sink with limited heat capacity,a cascade heating approach for obtaining high-temperature water is employed.A zeotropic refrigerant with temperature glide characteristics is selected as the working fluid.The modified heat exchange process reduces the temperature difference during heat transfer,thereby decreasing exergy destruction.A thermodynamic analysis model is established to assess the performance of the proposed autocascade heat pump cycle.The energy and exergy performances of the novel cycle are evaluated and compared with those of the basic cycle.Within the range of water outlet temperature considered here,the heating coefficient of performance and capacity increase by 51.1%and 50.6%,respectively.The proposed cycle decreases the mass flow rate of the refrigerant by 38.7%on average.For evaporating temperatures in the range 10-15℃,the proposed cycle improves the heating coefficient of performance and capacity by 54.7%and 43.9%over the basic cycle.The exergy analysis indicates that excellent exergy performance mainly benefits from the reductions in irreversible destruction between refrigerant and water heat exchange.Overall,the thermodynamic analysis reveals the improvements achieved with the novel auto-cascade heat pump cycle.
