The aim of the study is to investigate the influence of geometry on the thermal capacity and stratifications of a water pit heat storage for solar district heating.A TRNSYS component model for a truncated cone water p...The aim of the study is to investigate the influence of geometry on the thermal capacity and stratifications of a water pit heat storage for solar district heating.A TRNSYS component model for a truncated cone water pit was developed based on the coordinate transformation method and validated by experimental results from the water pit heat storage in Huangdicheng in 2018.The thermal performance of 26 water pits with different heights and side wall slopes was calculated for 10 consecutive years.It takes four to six years for the water pit to reach steady-state operation.The operation data from the tenth year was selected to evaluate the thermal performance of each configuration.The results show that because of the thermal insulation on top of the water pit,the height to diameter ratio of a water pit with minimum annual heat loss was always smaller than 1.0.The annual storage efficiency of a water pit increases with side wall slope due to the reduced side wall area.There is an almost linear increase in the thermal stratification number of a water pit with height.With an increase in the height,thermal stratification in water pits with a steeper slope increased more gradually than water pits with a lower slope.The findings in this paper are relevant for the design optimization of water pits as seasonal thermal energy storages.展开更多
A nonsimilarity analysis is performed to investigate the laminar, free convection boundary layer flow over a permeable isothermal truncated cone in the presence of a transverse magnetic field effect. A suitable set of...A nonsimilarity analysis is performed to investigate the laminar, free convection boundary layer flow over a permeable isothermal truncated cone in the presence of a transverse magnetic field effect. A suitable set of dimensionless variables is used and non-similar equations governing the problem are obtained. Fourth order Runge-Kutta with shooting technique is employed for the numerical solution of the obtained equations. Different water-based nanofluids containing Cu, Ag, CuO, Al2O3, and TiO2 are taken into consideration. The effects of pertinent parameters such as the solid volume fraction of nanoparticles, and magnetic field parameter have been investigated. Furthermore, different models of nanofluid based on different formulas for thermal conductivity and dynamic viscosity on the flow and heat transfer characteristics are discussed. Various comparisons with previously published work for the case of a vertical plate are performed and the results are found to be in excellent agreement.展开更多
基于VOF(Volume of Fluid)方法和有限体积法求解气、水两相流动的RANS方程,并结合动网格技术,对物体垂直入水空泡流动进行了数值计算研究。通过对球体垂直入水早期空泡形态进行数值计算,并将计算结果与May A理想空泡模型拟合结果进行对...基于VOF(Volume of Fluid)方法和有限体积法求解气、水两相流动的RANS方程,并结合动网格技术,对物体垂直入水空泡流动进行了数值计算研究。通过对球体垂直入水早期空泡形态进行数值计算,并将计算结果与May A理想空泡模型拟合结果进行对比分析,二者具有较好的一致性,验证了数值计算方法的有效性。在此基础之上,进一步研究了150°锥角回转体垂直入水空泡生成过程,空泡壁面运动特性和空泡表面闭合特性,给出了垂直匀速入水空泡形态随时间变化规律,空泡壁面随入水过程时间变化运动规律,以及空泡表面闭合时间与入水速度之间的关系。展开更多
本文提出一种基于圆台形吸收单元的超宽带、极化不敏感的超材料太赫兹吸收器.该超材料吸收器采用金属薄膜金和介质层二氧化硅交替叠加的多层结构.采用商业软件CST Studio Suite 2009时域求解器计算了其在0—10 THz波段内的吸收率A(ω),...本文提出一种基于圆台形吸收单元的超宽带、极化不敏感的超材料太赫兹吸收器.该超材料吸收器采用金属薄膜金和介质层二氧化硅交替叠加的多层结构.采用商业软件CST Studio Suite 2009时域求解器计算了其在0—10 THz波段内的吸收率A(ω),在2—10 THz之间实现了对入射太赫兹波的超宽频带强吸收.仿真结果表明,由于其圆台形单元结构,在器件垂直方向上形成一系列不同尺寸的微型吸收器,产生了吸收频点相连的多频吸收峰.利用不同吸收峰的耦合叠加效应,获得超过8 THz的超宽带太赫兹波吸收,吸收强度达到92.3%以上.这一结构具有超宽带强吸收,360极化不敏感以及易于加工等优越特性,因而在太赫兹波探测器、光谱成像以及隐身技术方面具有潜在的应用.展开更多
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA21050200)the Guangdong Innovative and Entrepreneurial Research Team Program(No.2013N070)the State Grid Corporation Science and Technology Project“Research on Comprehensive Development and Utilization Technology of Renewable Energy in Multi-format Ecological Development Zone”for funding this project.
文摘The aim of the study is to investigate the influence of geometry on the thermal capacity and stratifications of a water pit heat storage for solar district heating.A TRNSYS component model for a truncated cone water pit was developed based on the coordinate transformation method and validated by experimental results from the water pit heat storage in Huangdicheng in 2018.The thermal performance of 26 water pits with different heights and side wall slopes was calculated for 10 consecutive years.It takes four to six years for the water pit to reach steady-state operation.The operation data from the tenth year was selected to evaluate the thermal performance of each configuration.The results show that because of the thermal insulation on top of the water pit,the height to diameter ratio of a water pit with minimum annual heat loss was always smaller than 1.0.The annual storage efficiency of a water pit increases with side wall slope due to the reduced side wall area.There is an almost linear increase in the thermal stratification number of a water pit with height.With an increase in the height,thermal stratification in water pits with a steeper slope increased more gradually than water pits with a lower slope.The findings in this paper are relevant for the design optimization of water pits as seasonal thermal energy storages.
文摘A nonsimilarity analysis is performed to investigate the laminar, free convection boundary layer flow over a permeable isothermal truncated cone in the presence of a transverse magnetic field effect. A suitable set of dimensionless variables is used and non-similar equations governing the problem are obtained. Fourth order Runge-Kutta with shooting technique is employed for the numerical solution of the obtained equations. Different water-based nanofluids containing Cu, Ag, CuO, Al2O3, and TiO2 are taken into consideration. The effects of pertinent parameters such as the solid volume fraction of nanoparticles, and magnetic field parameter have been investigated. Furthermore, different models of nanofluid based on different formulas for thermal conductivity and dynamic viscosity on the flow and heat transfer characteristics are discussed. Various comparisons with previously published work for the case of a vertical plate are performed and the results are found to be in excellent agreement.
文摘基于VOF(Volume of Fluid)方法和有限体积法求解气、水两相流动的RANS方程,并结合动网格技术,对物体垂直入水空泡流动进行了数值计算研究。通过对球体垂直入水早期空泡形态进行数值计算,并将计算结果与May A理想空泡模型拟合结果进行对比分析,二者具有较好的一致性,验证了数值计算方法的有效性。在此基础之上,进一步研究了150°锥角回转体垂直入水空泡生成过程,空泡壁面运动特性和空泡表面闭合特性,给出了垂直匀速入水空泡形态随时间变化规律,空泡壁面随入水过程时间变化运动规律,以及空泡表面闭合时间与入水速度之间的关系。
文摘本文提出一种基于圆台形吸收单元的超宽带、极化不敏感的超材料太赫兹吸收器.该超材料吸收器采用金属薄膜金和介质层二氧化硅交替叠加的多层结构.采用商业软件CST Studio Suite 2009时域求解器计算了其在0—10 THz波段内的吸收率A(ω),在2—10 THz之间实现了对入射太赫兹波的超宽频带强吸收.仿真结果表明,由于其圆台形单元结构,在器件垂直方向上形成一系列不同尺寸的微型吸收器,产生了吸收频点相连的多频吸收峰.利用不同吸收峰的耦合叠加效应,获得超过8 THz的超宽带太赫兹波吸收,吸收强度达到92.3%以上.这一结构具有超宽带强吸收,360极化不敏感以及易于加工等优越特性,因而在太赫兹波探测器、光谱成像以及隐身技术方面具有潜在的应用.
