并行I/O技术有效优化了I/O性能,但对访问延迟却难以控制.相变存储器(phase change memory,PCM)作为一种SCM(storage class memory),具有非易失性、随机可读写、低延迟、高吞吐率、体积小和低功耗的特点,为I/O性能优化提供了最直接有效...并行I/O技术有效优化了I/O性能,但对访问延迟却难以控制.相变存储器(phase change memory,PCM)作为一种SCM(storage class memory),具有非易失性、随机可读写、低延迟、高吞吐率、体积小和低功耗的特点,为I/O性能优化提供了最直接有效的途径.研究了PCM的特性与存在的问题,总结了目前PCM的应用研究进展,针对高性能计算中的并行I/O问题,提出了一种基于相变存储器PCM的层次式并行混合存储模型,能够有效提高并行文件系统元数据服务效率和并行I/O吞吐率.展开更多
Based on the lowest melting point and Schroeder’s theoretical calculation formula,nano- modified organic composite phase change materials（PCMs）were prepared.The phase transition temperature and the latent heat of t...Based on the lowest melting point and Schroeder’s theoretical calculation formula,nano- modified organic composite phase change materials（PCMs）were prepared.The phase transition temperature and the latent heat of the materials were 24℃and 172 J/g,respectively.A new shape-stabilized phase change materials were prepared,using high density polyethylene as supporting material.The PCM kept the shape when temperature was higher than melting point.Thus,it can directly contact with heat transfer media.The structure,morphology and thermal behavior of PCM were analyzed by FTIR,SEM and DSC.展开更多
The usage of phase change materials (PCM) to store the heat in the form of latent heat is increased, because large quantity of thermal energy is stored in smaller volumes. In the present experimental investigation, so...The usage of phase change materials (PCM) to store the heat in the form of latent heat is increased, because large quantity of thermal energy is stored in smaller volumes. In the present experimental investigation, sodium thiosulphate pentahydrate is employed as phase change material and it is stored in stainless steel capsules. These capsules are kept in fabricated tank and hot water is supplied into it. The experimental design is prepared by considering the parameters: flow rate, heat transfer fluid inlet temperature and PCM capsule shape. Experiments are conducted according to the experimental design and responses are recorded. The effect of selected parameters on TES using PCM is studied by analyzing experimental data. The experimental data are also analyzed using Fuzzy Logic to find the optimal values of flow rate, heat transfer fluid inlet temperature and PCM capsule shapes. The present work utilizes Fuzzy Logic to find the optimal parameters for designing the effective Thermal Energy Storage System (TES).展开更多
A comprehensive numerical study was conducted to investigate heat transfer enhancement during the melting process in a 2D square cavity through dispersion of nanoparticles.A paraffin-based nanofluid containing various...A comprehensive numerical study was conducted to investigate heat transfer enhancement during the melting process in a 2D square cavity through dispersion of nanoparticles.A paraffin-based nanofluid containing various volume fractions of Cu was applied.The governing equations were solved on a non-uniform mesh using a pressure-based finite volume method with an enthalpy porosity technique to trace the solid-liquid interface.The effects of nanoparticle dispersion in a pure fluid and of some significant parameters,namely nanoparticle volume fraction,cavity size and hot wall temperature,on the fluid flow,heat transfer features and melting time were studied.The results are presented in terms of temperature and velocity profiles,streamlines,isotherms,moving interface position,solid fraction and dimensionless heat flux.The suspended nanoparticles caused an increase in thermal conductivity of nano-enhanced phase change material(NEPCM)compared to conventional PCM,resulting in heat transfer enhancement and a higher melting rate.In addition,the nanofluid heat transfer rate increased and the melting time decreased as the volume fraction of nanoparticles increased.The higher temperature difference between the melting temperature and the hot wall temperature expedited the melting process of NEPCM.展开更多
Obviously, the outside annual climate change caused either by a major solar input during the hottest period or by a temperature drop during the coldest period leads to discomfort in inside buildings. This effect can b...Obviously, the outside annual climate change caused either by a major solar input during the hottest period or by a temperature drop during the coldest period leads to discomfort in inside buildings. This effect can be reduced by storing heat transmitted in phase change materials (PCM) as latent heat, in order to ensure a good situation of thermal comfort during all months of the year. In this work, thermal behavior of two roofing systems is studied. One roof is constituted only by usual materials in building. In the other, two phase change materials (PCM) are introduced according to three configurations. Study is interested to assess incorporation effect of two PCMs within the roof and to evaluate the optimum locations to reduce the energy consumption of air-conditioned room. Mono-dimensional numerical model validated analytically and experimentally, is used to carry out a parametric analyzes to determine characteristics of the layers in which the roofs are formed regardless of external climate effect. Numerical calculations are performed for three configurations of roof. Results show that insertion of phase change materials in roof provides best energy consumption saving regardless annual climate change. Generally, the three configurations lead to different results, depending on the combination of PCMs. This difference becomes less important when selection of PCMs take account the thermal comfort level and temperatures of hottest and coldest periods.展开更多
The Green＇s function method is applied for the transient temperature of an annular fin when a phase change material （PCM） solidifies on it. The solidification of the PCMs takes place in a cylindrical shell storage....The Green＇s function method is applied for the transient temperature of an annular fin when a phase change material （PCM） solidifies on it. The solidification of the PCMs takes place in a cylindrical shell storage. The thickness of the solid PCM on the fin varies with time and is obtained by the Megerlin method. The models are found with the Bessel equation to form an analytical solution. Three different kinds of boundary conditions are investigated. The comparison between analytical and numerical solutions is given. The results demonstrate that the significant accuracy is obtained for the temperature distribution for the fin in all cases.展开更多
A thermal heat storage system with an energy content of 40 kWh and a temperature of 58°C will be presented. This storage system is suitable for supporting the use of renewable energies in buildings and for absorb...A thermal heat storage system with an energy content of 40 kWh and a temperature of 58°C will be presented. This storage system is suitable for supporting the use of renewable energies in buildings and for absorbing solar heat, heat from co-generation and heat pumps or electric heat from excess wind and solar power. The storage system is equipped with a plate heat exchanger that is so powerful that even with small temperature differences between the flow temperature and the storage temperature a high load dynamic is achieved. The storage system has a performance of 2.8 kW at 4 K and 10.6 kW at a temperature difference of 10 K. Thus, large performance variations in solar thermal systems or CHP plants can be buffered very well. Further a storage charge function Q(T, t) will be presented to characterize the performance of the storage.展开更多
文摘针对采用单一冷却方式的锂离子电池模组LIBM(lithium-ion battery module)冷却效果不佳的问题,提出了1种相变材料PCM(phase change material)风冷耦合电池冷却系统。讨论了不同入口空气风速IAV(inlet air velocity)、不同电池间隙BG(battery gap)和不同入口空气温度IAT(inlet air temperature)对LIBM内最高温度和最大温差的影响;以IAV、BG和IAT为设计变量,以最高温度和最大温差为目标函数,通过响应面模型对设计变量与目标函数进行了数值拟合;采用非支配排序遗传算法对响应面模型进行了优化预测;利用计算流体力学仿真对优化预测结果进行了验证。结果表明,经过优化后的冷却系统能将LIBM内的最高温度降低4.68℃(13.8%),最大温差降低0.57℃(30.3%)。
文摘并行I/O技术有效优化了I/O性能,但对访问延迟却难以控制.相变存储器(phase change memory,PCM)作为一种SCM(storage class memory),具有非易失性、随机可读写、低延迟、高吞吐率、体积小和低功耗的特点,为I/O性能优化提供了最直接有效的途径.研究了PCM的特性与存在的问题,总结了目前PCM的应用研究进展,针对高性能计算中的并行I/O问题,提出了一种基于相变存储器PCM的层次式并行混合存储模型,能够有效提高并行文件系统元数据服务效率和并行I/O吞吐率.
基金Funded by the National Key Technologies Research and Development Program of China(No.2006BAJ04A16)
文摘Based on the lowest melting point and Schroeder’s theoretical calculation formula,nano- modified organic composite phase change materials（PCMs）were prepared.The phase transition temperature and the latent heat of the materials were 24℃and 172 J/g,respectively.A new shape-stabilized phase change materials were prepared,using high density polyethylene as supporting material.The PCM kept the shape when temperature was higher than melting point.Thus,it can directly contact with heat transfer media.The structure,morphology and thermal behavior of PCM were analyzed by FTIR,SEM and DSC.
文摘The usage of phase change materials (PCM) to store the heat in the form of latent heat is increased, because large quantity of thermal energy is stored in smaller volumes. In the present experimental investigation, sodium thiosulphate pentahydrate is employed as phase change material and it is stored in stainless steel capsules. These capsules are kept in fabricated tank and hot water is supplied into it. The experimental design is prepared by considering the parameters: flow rate, heat transfer fluid inlet temperature and PCM capsule shape. Experiments are conducted according to the experimental design and responses are recorded. The effect of selected parameters on TES using PCM is studied by analyzing experimental data. The experimental data are also analyzed using Fuzzy Logic to find the optimal values of flow rate, heat transfer fluid inlet temperature and PCM capsule shapes. The present work utilizes Fuzzy Logic to find the optimal parameters for designing the effective Thermal Energy Storage System (TES).
文摘A comprehensive numerical study was conducted to investigate heat transfer enhancement during the melting process in a 2D square cavity through dispersion of nanoparticles.A paraffin-based nanofluid containing various volume fractions of Cu was applied.The governing equations were solved on a non-uniform mesh using a pressure-based finite volume method with an enthalpy porosity technique to trace the solid-liquid interface.The effects of nanoparticle dispersion in a pure fluid and of some significant parameters,namely nanoparticle volume fraction,cavity size and hot wall temperature,on the fluid flow,heat transfer features and melting time were studied.The results are presented in terms of temperature and velocity profiles,streamlines,isotherms,moving interface position,solid fraction and dimensionless heat flux.The suspended nanoparticles caused an increase in thermal conductivity of nano-enhanced phase change material(NEPCM)compared to conventional PCM,resulting in heat transfer enhancement and a higher melting rate.In addition,the nanofluid heat transfer rate increased and the melting time decreased as the volume fraction of nanoparticles increased.The higher temperature difference between the melting temperature and the hot wall temperature expedited the melting process of NEPCM.
文摘Obviously, the outside annual climate change caused either by a major solar input during the hottest period or by a temperature drop during the coldest period leads to discomfort in inside buildings. This effect can be reduced by storing heat transmitted in phase change materials (PCM) as latent heat, in order to ensure a good situation of thermal comfort during all months of the year. In this work, thermal behavior of two roofing systems is studied. One roof is constituted only by usual materials in building. In the other, two phase change materials (PCM) are introduced according to three configurations. Study is interested to assess incorporation effect of two PCMs within the roof and to evaluate the optimum locations to reduce the energy consumption of air-conditioned room. Mono-dimensional numerical model validated analytically and experimentally, is used to carry out a parametric analyzes to determine characteristics of the layers in which the roofs are formed regardless of external climate effect. Numerical calculations are performed for three configurations of roof. Results show that insertion of phase change materials in roof provides best energy consumption saving regardless annual climate change. Generally, the three configurations lead to different results, depending on the combination of PCMs. This difference becomes less important when selection of PCMs take account the thermal comfort level and temperatures of hottest and coldest periods.
文摘The Green＇s function method is applied for the transient temperature of an annular fin when a phase change material （PCM） solidifies on it. The solidification of the PCMs takes place in a cylindrical shell storage. The thickness of the solid PCM on the fin varies with time and is obtained by the Megerlin method. The models are found with the Bessel equation to form an analytical solution. Three different kinds of boundary conditions are investigated. The comparison between analytical and numerical solutions is given. The results demonstrate that the significant accuracy is obtained for the temperature distribution for the fin in all cases.
文摘A thermal heat storage system with an energy content of 40 kWh and a temperature of 58°C will be presented. This storage system is suitable for supporting the use of renewable energies in buildings and for absorbing solar heat, heat from co-generation and heat pumps or electric heat from excess wind and solar power. The storage system is equipped with a plate heat exchanger that is so powerful that even with small temperature differences between the flow temperature and the storage temperature a high load dynamic is achieved. The storage system has a performance of 2.8 kW at 4 K and 10.6 kW at a temperature difference of 10 K. Thus, large performance variations in solar thermal systems or CHP plants can be buffered very well. Further a storage charge function Q(T, t) will be presented to characterize the performance of the storage.
