在系统压力P=412~850 k Pa,过冷度?Tsub=4.7~15.0℃,热通量q"=0.11~10.90 k W·m^(-2),质量流量G=147.5~443.7 kg·m^(-2)·s-1的条件下,对立式和卧式螺旋管内R134a过冷流动沸腾起始点特性进行了实验研究。研究结果表...在系统压力P=412~850 k Pa,过冷度?Tsub=4.7~15.0℃,热通量q"=0.11~10.90 k W·m^(-2),质量流量G=147.5~443.7 kg·m^(-2)·s-1的条件下,对立式和卧式螺旋管内R134a过冷流动沸腾起始点特性进行了实验研究。研究结果表明:当实验系统参数相同时,立式和卧式螺旋管内过冷沸腾起始点的热通量基本相同,但是立式螺旋管内过冷沸腾起始点壁面过热度小于卧式螺旋管;过冷沸腾起始点的热通量、壁面过热度随着过冷度和质量流量的增大而增大,但随着压力、螺旋直径的增大而减小。通过无量纲分析对实验数据进行非线性拟合,发展了适用于螺旋管过冷沸腾起始点的关联式。展开更多
The experiments of the onset of nucleate boiling using R134a as working fluid were conducted in vertical helically-coiled tubes. The experiments were carried out with a range of pressure from 450 to 850 kPa, inlet sub...The experiments of the onset of nucleate boiling using R134a as working fluid were conducted in vertical helically-coiled tubes. The experiments were carried out with a range of pressure from 450 to 850 kPa, inlet subcooling from 4.7 to 15.0℃, heat flux from 0.11 to 8.9 kW/m2 and mass flux from 218. 2 to 443. 7 kg/（ m2 · s ）. The heat flux, superheat and temperature undershoot at the ONB are analyzed in vertical helically-coiled tubes. Also, the effects of mass flux, system pressure, inlet subcooling and geometric parameters on the ONB are studied. The results demonstrate that the inception heat flux and superheat increase with increasing mass flux and inlet subcooling, but decrease with increasing system pressure and helix diameter. The pitch of the helical coil has a slight effect on the wall superheat and heat flux at the ONB. The correlation of heat flux at the ONB of subcooled flow boiling in helical coil is developed based on the experimental data, and it shows a good agreement with the experimental data.展开更多
A two temperature CO_(2) refrigeration system with economizer is proposed and compared with the traditional dual-temperature CO_(2) refrigeration system based on energy consumption,exergy and economic analysis.Using g...A two temperature CO_(2) refrigeration system with economizer is proposed and compared with the traditional dual-temperature CO_(2) refrigeration system based on energy consumption,exergy and economic analysis.Using genetic algorithm multi-objective optimization method,taking the COP,exergy loss and total economic cost as the objective functions to find the best design conditions of the two systems.The Pareto fronts are obtained at different ambient temperatures.Technique for order preference by similarity to an ideal solution decision-making method is adopted to determine the optimum state points.The simulation results show that when operating at different ambient temperatures,the introduction of economizer can improve COP,reduce exergy loss and the overall economic cost rate of the two-temperature CO_(2) refrigeration system.In addition,economic analyses take the impact of carbon dioxide emission cost and electricity price into consideration.The results indicate that with the increase of CO_(2) emission cost and electricity price,the hourly economic cost of both systems increases,but the hourly economic cost of the two-temperature CO_(2) refrigeration system with economizer system is always lower than that of conventional two-temperature CO_(2) refrigeration system.展开更多
The basic organic Rankine cycle(BORC)and ORC with an internal heat exchanger(IHORC)are studied with different working fluids under a given heat source condition to analyse the thermodynamic performances and net power ...The basic organic Rankine cycle(BORC)and ORC with an internal heat exchanger(IHORC)are studied with different working fluids under a given heat source condition to analyse the thermodynamic performances and net power output.The results demonstrate that the external exergy efficiency of IHORC is lower than that of BORC while the internal exergy efficiency is on the opposite with the same overall exergy efficiencies.A multi-objective optimization model with inlet pressure and temperature of expander as independent parameters and exergy and heat recovery efficiencies as objective functions is solved by NSGA-II(the second non-dominated sorting genetic algorithm).The Pareto optimal solutions are obtained by the optimization models.By calculation with the optimum conditions,it is determined that R236ea has the best comprehensive performance with exergy efficiencies being 40.69%and 41.38%,and heat recovery efficiencies being 83.2%and 75.6%in IHORC and BORC,respectively.The evaporators occupy the maximum exergy destruction,which can be reduced by decreasing pinch point temperatures and increasing evaporation pressures.展开更多
A pump is needed in an ejector refrigeration system,which makes the system high cost and complicated and hinders its application.A pump-free double heat source ejector refrigeration system using R1234yf as working flu...A pump is needed in an ejector refrigeration system,which makes the system high cost and complicated and hinders its application.A pump-free double heat source ejector refrigeration system using R1234yf as working fluid is proposed in which an injector driven by another heat source replaces the liquid circulating pump,making the system more affordable,simpler and more stable.The effect of different operation conditions on entrainment ratios and the influence of different factors on system performance are analyzed on the basis of mass,momentum and energy conservation equations.The influence degree of each factor on system performance is investigated by the orthogonal test method.The condenser temperature has the largest effect on system performance.The pressure drop in the suction chamber of gas-liquid injector has the least impact on system performance.The COP can reach about 0.35 under a certain working condition.The system can be driven by two different temperature heat sources with no electricity needed,and it is a good choice for places with abundant heat resources or lack of electricity.展开更多
文摘在系统压力P=412~850 k Pa,过冷度?Tsub=4.7~15.0℃,热通量q"=0.11~10.90 k W·m^(-2),质量流量G=147.5~443.7 kg·m^(-2)·s-1的条件下,对立式和卧式螺旋管内R134a过冷流动沸腾起始点特性进行了实验研究。研究结果表明:当实验系统参数相同时,立式和卧式螺旋管内过冷沸腾起始点的热通量基本相同,但是立式螺旋管内过冷沸腾起始点壁面过热度小于卧式螺旋管;过冷沸腾起始点的热通量、壁面过热度随着过冷度和质量流量的增大而增大,但随着压力、螺旋直径的增大而减小。通过无量纲分析对实验数据进行非线性拟合,发展了适用于螺旋管过冷沸腾起始点的关联式。
基金The National Natural Science Foundation of China(No.50776055,51076084)the Natural Science Foundation of Shandong Province(No.ZR2016YL005)
文摘The experiments of the onset of nucleate boiling using R134a as working fluid were conducted in vertical helically-coiled tubes. The experiments were carried out with a range of pressure from 450 to 850 kPa, inlet subcooling from 4.7 to 15.0℃, heat flux from 0.11 to 8.9 kW/m2 and mass flux from 218. 2 to 443. 7 kg/（ m2 · s ）. The heat flux, superheat and temperature undershoot at the ONB are analyzed in vertical helically-coiled tubes. Also, the effects of mass flux, system pressure, inlet subcooling and geometric parameters on the ONB are studied. The results demonstrate that the inception heat flux and superheat increase with increasing mass flux and inlet subcooling, but decrease with increasing system pressure and helix diameter. The pitch of the helical coil has a slight effect on the wall superheat and heat flux at the ONB. The correlation of heat flux at the ONB of subcooled flow boiling in helical coil is developed based on the experimental data, and it shows a good agreement with the experimental data.
基金supported by the National Natural Science Foundation of China (Grant No. 51776110)。
文摘A two temperature CO_(2) refrigeration system with economizer is proposed and compared with the traditional dual-temperature CO_(2) refrigeration system based on energy consumption,exergy and economic analysis.Using genetic algorithm multi-objective optimization method,taking the COP,exergy loss and total economic cost as the objective functions to find the best design conditions of the two systems.The Pareto fronts are obtained at different ambient temperatures.Technique for order preference by similarity to an ideal solution decision-making method is adopted to determine the optimum state points.The simulation results show that when operating at different ambient temperatures,the introduction of economizer can improve COP,reduce exergy loss and the overall economic cost rate of the two-temperature CO_(2) refrigeration system.In addition,economic analyses take the impact of carbon dioxide emission cost and electricity price into consideration.The results indicate that with the increase of CO_(2) emission cost and electricity price,the hourly economic cost of both systems increases,but the hourly economic cost of the two-temperature CO_(2) refrigeration system with economizer system is always lower than that of conventional two-temperature CO_(2) refrigeration system.
基金supported by projects for International(regional)Cooperation and Exchange of the National Natural-Science Foundation of China(Grant No.41761144067)the National Natural Science Foundation of China(Grant No.51376110)。
文摘The basic organic Rankine cycle(BORC)and ORC with an internal heat exchanger(IHORC)are studied with different working fluids under a given heat source condition to analyse the thermodynamic performances and net power output.The results demonstrate that the external exergy efficiency of IHORC is lower than that of BORC while the internal exergy efficiency is on the opposite with the same overall exergy efficiencies.A multi-objective optimization model with inlet pressure and temperature of expander as independent parameters and exergy and heat recovery efficiencies as objective functions is solved by NSGA-II(the second non-dominated sorting genetic algorithm).The Pareto optimal solutions are obtained by the optimization models.By calculation with the optimum conditions,it is determined that R236ea has the best comprehensive performance with exergy efficiencies being 40.69%and 41.38%,and heat recovery efficiencies being 83.2%and 75.6%in IHORC and BORC,respectively.The evaporators occupy the maximum exergy destruction,which can be reduced by decreasing pinch point temperatures and increasing evaporation pressures.
基金supported by the National Natural Science Foundation of China(Grant No.51776110)the Fundamental Research Funds of Shandong University(Grant No.2017JC037)。
文摘A pump is needed in an ejector refrigeration system,which makes the system high cost and complicated and hinders its application.A pump-free double heat source ejector refrigeration system using R1234yf as working fluid is proposed in which an injector driven by another heat source replaces the liquid circulating pump,making the system more affordable,simpler and more stable.The effect of different operation conditions on entrainment ratios and the influence of different factors on system performance are analyzed on the basis of mass,momentum and energy conservation equations.The influence degree of each factor on system performance is investigated by the orthogonal test method.The condenser temperature has the largest effect on system performance.The pressure drop in the suction chamber of gas-liquid injector has the least impact on system performance.The COP can reach about 0.35 under a certain working condition.The system can be driven by two different temperature heat sources with no electricity needed,and it is a good choice for places with abundant heat resources or lack of electricity.
