It is necessary to satisfy the flexible requirements of solar heat storage systems to provide efficient heating and constant-temperature domestic hot water at different periods.A novel heat storage tank with both stra...It is necessary to satisfy the flexible requirements of solar heat storage systems to provide efficient heating and constant-temperature domestic hot water at different periods.A novel heat storage tank with both stratified and mixing functions is proposed,which can realize the integration of stable stratification and rapid mixing modes.In this research,a three-dimensional heat transfer model of the heat storage tank with stratified and mixed dual modes was established,and a thermal performance test system for the tank was built in the State Key Laboratory of Green Building in Western China.Moreover,a new evaluation index representing the mixing speed is proposed.The stratification effect and mixing characteristics of the tank were studied under different comprehensive conditions.The results show that the exergy efficiency of the tank with a stratified pipe can be increased by 10%–15%compared to that of a conventional tank.Additionally,the recommended optimal flow rate range for well-stratified tanks is 4–6 L/min.The mixing nozzle of the tank reduces the mixing reaction coefficient by 0.27 and significantly reduces the mixing time.This study provides critical guidance to meet the flexible thermal needs of users and implement high-performance applications using the stratified and mixing modes of heat storage tanks.展开更多
Improving the flexibility of combined heat and power(CHP)units is an important way to solve the problem of wind power accommodation in northern China.Firstly,this paper analyzes the principle of an extraction-type CHP...Improving the flexibility of combined heat and power(CHP)units is an important way to solve the problem of wind power accommodation in northern China.Firstly,this paper analyzes the principle of an extraction-type CHP unit,calculates its safe operation range,and analyzes its contradiction between heating and peaking.Secondly,the safe operation ranges of the CHP unit with several flexibility modifications are further calculated,which involve two-stage bypass,low-pressure cylinder(LPC)removal,heat storage tank,and electric boiler.Finally,based on the safe operation ranges,their effects on improving the capabilities of deep peak shaving and wind power accommodation are compared,and their adaptabilities to different wind scenarios are analyzed.The results show that:①all flexibility modifications can improve the deep peak shaving capability of the CHP unit,especially for the two-stage bypass and the electric boiler;②LPC removal modification can accommodate wind power to some extent,but most of wind power is still abandoned;③heat storage tank modification is unstable in different wind scenarios,which is determined by the surplus heating capability during the daytime.展开更多
基金the National Natural Science Foundation of China(No.52078408,No.51908442)the State Key Program of National Natural Science Foundation of China(No.U20A20311)the Science Foundation for Outstanding Youth of Shaanxi Province(No.2020JC-43).
文摘It is necessary to satisfy the flexible requirements of solar heat storage systems to provide efficient heating and constant-temperature domestic hot water at different periods.A novel heat storage tank with both stratified and mixing functions is proposed,which can realize the integration of stable stratification and rapid mixing modes.In this research,a three-dimensional heat transfer model of the heat storage tank with stratified and mixed dual modes was established,and a thermal performance test system for the tank was built in the State Key Laboratory of Green Building in Western China.Moreover,a new evaluation index representing the mixing speed is proposed.The stratification effect and mixing characteristics of the tank were studied under different comprehensive conditions.The results show that the exergy efficiency of the tank with a stratified pipe can be increased by 10%–15%compared to that of a conventional tank.Additionally,the recommended optimal flow rate range for well-stratified tanks is 4–6 L/min.The mixing nozzle of the tank reduces the mixing reaction coefficient by 0.27 and significantly reduces the mixing time.This study provides critical guidance to meet the flexible thermal needs of users and implement high-performance applications using the stratified and mixing modes of heat storage tanks.
基金supported in part by the National Natural Science Foundation of China(No.51806063)。
文摘Improving the flexibility of combined heat and power(CHP)units is an important way to solve the problem of wind power accommodation in northern China.Firstly,this paper analyzes the principle of an extraction-type CHP unit,calculates its safe operation range,and analyzes its contradiction between heating and peaking.Secondly,the safe operation ranges of the CHP unit with several flexibility modifications are further calculated,which involve two-stage bypass,low-pressure cylinder(LPC)removal,heat storage tank,and electric boiler.Finally,based on the safe operation ranges,their effects on improving the capabilities of deep peak shaving and wind power accommodation are compared,and their adaptabilities to different wind scenarios are analyzed.The results show that:①all flexibility modifications can improve the deep peak shaving capability of the CHP unit,especially for the two-stage bypass and the electric boiler;②LPC removal modification can accommodate wind power to some extent,but most of wind power is still abandoned;③heat storage tank modification is unstable in different wind scenarios,which is determined by the surplus heating capability during the daytime.
