To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles(ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area(UHEA) net p...To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles(ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area(UHEA) net power, embodying the cost/performance ratio of an ORC system, was proposed as a new indicator to judge the suitability of ORC working fluids on a given condition. The heat exchange area was computed by an improved evaporator model without fixing the minimum temperature difference between working fluid and hot fluid, and the flow pattern transition during heat exchange was also taken into account. The maximum UHEA net powers obtained show that dry organic fluids are more suitable for ORCs than wet organic fluids to recover low-temperature heat. The organic fluid 1-butene is recommended if the inlet temperature of hot fluid is 353.15-363.15 K or443.15-453.15 K, heptane is more suitable at 373.15-423.15 K, and R245 ca is a good option at 483.15-503.15 K.展开更多
China’s urban expansion,food security,and energy transition are in a critical situation.One solution is to tap into the green production potential of the built urban environment and explore new ways to save land spac...China’s urban expansion,food security,and energy transition are in a critical situation.One solution is to tap into the green production potential of the built urban environment and explore new ways to save land space and alleviate ecological pressure through food and solar energy production.This paper differs from previous ecological compensation studies,which mostly focus on key ecological functional areas or fiscal compensation mechanisms,in that it innovatively establishes an ecological compensation mechanism within the urban space.In this paper,we propose the"green productive area"of cities as a way to measure the ecological carrying capacity improvement potential of cities from the perspective of urban ecology,and it is based on converting the green resource income of cities into the ecological footprint area they could save under the same conditions.First,a typological approach was used to establish a compensation strategy for green production.Second,a spatial inventory was taken of all elements of the built environment and an analysis of their green production potential was carried out.Finally,it was necessary to establish a unified accounting standard for the ecological land saving benefits of different green production options,which could be converted into green productive land area indicators.In the case of Xuefu Street in Nankai District,Tianjin,the available rooftops and idle land were used for green production,which supplemented the ecological carrying capacity provided by the natural land occupied by 12%of the buildings in the district.展开更多
基金Projects(U0937604,50876116)supported by the National Natural Science Foundation of ChinaProjects(2010QZZD0107,2014zzts192)supported by the Fundamental Research Funds for the Central Universities of China
文摘To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles(ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area(UHEA) net power, embodying the cost/performance ratio of an ORC system, was proposed as a new indicator to judge the suitability of ORC working fluids on a given condition. The heat exchange area was computed by an improved evaporator model without fixing the minimum temperature difference between working fluid and hot fluid, and the flow pattern transition during heat exchange was also taken into account. The maximum UHEA net powers obtained show that dry organic fluids are more suitable for ORCs than wet organic fluids to recover low-temperature heat. The organic fluid 1-butene is recommended if the inlet temperature of hot fluid is 353.15-363.15 K or443.15-453.15 K, heptane is more suitable at 373.15-423.15 K, and R245 ca is a good option at 483.15-503.15 K.
基金The National Natural Science Foundation of China(51978443,52078322)The Youth Program of National Natural Science Foundation ofChina(51708395)The Tianjin Graduate Research and Innovation Project in 2009(2019YJSB175).
文摘China’s urban expansion,food security,and energy transition are in a critical situation.One solution is to tap into the green production potential of the built urban environment and explore new ways to save land space and alleviate ecological pressure through food and solar energy production.This paper differs from previous ecological compensation studies,which mostly focus on key ecological functional areas or fiscal compensation mechanisms,in that it innovatively establishes an ecological compensation mechanism within the urban space.In this paper,we propose the"green productive area"of cities as a way to measure the ecological carrying capacity improvement potential of cities from the perspective of urban ecology,and it is based on converting the green resource income of cities into the ecological footprint area they could save under the same conditions.First,a typological approach was used to establish a compensation strategy for green production.Second,a spatial inventory was taken of all elements of the built environment and an analysis of their green production potential was carried out.Finally,it was necessary to establish a unified accounting standard for the ecological land saving benefits of different green production options,which could be converted into green productive land area indicators.In the case of Xuefu Street in Nankai District,Tianjin,the available rooftops and idle land were used for green production,which supplemented the ecological carrying capacity provided by the natural land occupied by 12%of the buildings in the district.
