In order to solve the flow mismatch problem between pumping source output and workload demand,a novel configuration of D + A combined multi-pump controlled hydraulic system,similar to a pump-controlled system,is propo...In order to solve the flow mismatch problem between pumping source output and workload demand,a novel configuration of D + A combined multi-pump controlled hydraulic system,similar to a pump-controlled system,is proposed for a large power hydraulic system in this study. This novel configuration consists of several parallel fixed displacement pumps of different sizes and proportional variable displacement pumps,which is controlled by digital signal( on/off) and analog signal respectively( D + A pumps). The system flow is divided into two parts,one is the total flow from fixed displacement pumps,and the other is the rest desired flow supplied by variable displacement pumps to smooth and improve the demand flow. First,basic design principles and evaluation indicators of the proposed system are introduced. Then,a flow state matrix of the binary-coding digital pumps( 1: 2: 4) is obtained to provide the control signals of pumps. Experimental results show that the system output flow tracks well with acceptable flow deviation,though a little lag behind input signal.展开更多
There is a critical need to develop advanced high-temperature thermal storage systems to improve efficiencies and reduce the costs of solar thermal storage system.In this work,two typical systems composed with Cu as m...There is a critical need to develop advanced high-temperature thermal storage systems to improve efficiencies and reduce the costs of solar thermal storage system.In this work,two typical systems composed with Cu as matrix and Sn as the phase change material(PCM)are explored,namely,the 3-deimentional(3D)structure system by embedding Sn particles into Cu matrix and the 2-deimentional(2D)structure system by embedding Sn wires into Cu matrix.Given the thermophysical properties of a nanomaterial could be importantly different from that of a bulk one,we thus firstly derive the thermophysical properties of PCM and matrix theoretically,like the thermal conductivity by kinetic method and the specific heat capacity based on Lindemann’s criterion.And then,these properties are utilized to estimate the energy storage ability in both 3D and 2D structure system,and the influence of structure on heat transfer efficiency is theoretically investigated in both 3D and 2D structure system.Results turn out that 3D structure system is a better choice than a 2D structure system,because of larger specific surface area,a larger sensitive heat capacity and a larger thermal conductivity.When the feature size of the PCM decreases to be less than a critical value which is about 500 nm for Sn,the thermal conductivity of the system decreases exponentially while the heat storage capacity increases lineally.Moreover,when the feature size of Sn geometry is less than a critical value,which is 15 nm for 3D structure system and 25 nm for 2D structure,the Cu matrix can’t play a role in improving the effective thermal conductivity of the whole system.展开更多
Thermal energy storage(TES) is an attention-gaining technology which is useful to improve the energy efficiency as well as to balance the energy supply and demand. Until recently, the latent heat TES(LHTES) technology...Thermal energy storage(TES) is an attention-gaining technology which is useful to improve the energy efficiency as well as to balance the energy supply and demand. Until recently, the latent heat TES(LHTES) technology has been promoted quite fast mainly due to the large heat storage/release capacity that takes place at nearly constant temperature. The phase change slurry(PCS) prepared by dispersing phase change materials(PCMs) into carrying fluid can serve not only as the energy storage media, but also as the heat transfer fluid(HTF). Compared with the conventional PCM which needs additional HTF, the PCS provides superior performance and has the great potential to upgrade the current TES systems. This paper reviews the latest investigations of the micro-encapsulated PCM(MPCM) and shape-stabilized PCM(SSPCM) slurries. A brief introduction of the preparation methods of the two types of the PCSs is summarized. And a comprehensive review of the flow and heat transfer characteristics of the PCSs, particularly in various tube-based geometries and heat exchangers, is conducted for a better understanding of the mechanism and further utilization of the next-generation TES systems.展开更多
基金Supported by the National Natural Science Foundation of China(No.51575471)the Key Project of Natural Science Foundation of Hebei Province(No.E2016203264)
文摘In order to solve the flow mismatch problem between pumping source output and workload demand,a novel configuration of D + A combined multi-pump controlled hydraulic system,similar to a pump-controlled system,is proposed for a large power hydraulic system in this study. This novel configuration consists of several parallel fixed displacement pumps of different sizes and proportional variable displacement pumps,which is controlled by digital signal( on/off) and analog signal respectively( D + A pumps). The system flow is divided into two parts,one is the total flow from fixed displacement pumps,and the other is the rest desired flow supplied by variable displacement pumps to smooth and improve the demand flow. First,basic design principles and evaluation indicators of the proposed system are introduced. Then,a flow state matrix of the binary-coding digital pumps( 1: 2: 4) is obtained to provide the control signals of pumps. Experimental results show that the system output flow tracks well with acceptable flow deviation,though a little lag behind input signal.
基金supported by the Fundamental Research Funds for the Central Universities(2020ZDPY0215)。
文摘There is a critical need to develop advanced high-temperature thermal storage systems to improve efficiencies and reduce the costs of solar thermal storage system.In this work,two typical systems composed with Cu as matrix and Sn as the phase change material(PCM)are explored,namely,the 3-deimentional(3D)structure system by embedding Sn particles into Cu matrix and the 2-deimentional(2D)structure system by embedding Sn wires into Cu matrix.Given the thermophysical properties of a nanomaterial could be importantly different from that of a bulk one,we thus firstly derive the thermophysical properties of PCM and matrix theoretically,like the thermal conductivity by kinetic method and the specific heat capacity based on Lindemann’s criterion.And then,these properties are utilized to estimate the energy storage ability in both 3D and 2D structure system,and the influence of structure on heat transfer efficiency is theoretically investigated in both 3D and 2D structure system.Results turn out that 3D structure system is a better choice than a 2D structure system,because of larger specific surface area,a larger sensitive heat capacity and a larger thermal conductivity.When the feature size of the PCM decreases to be less than a critical value which is about 500 nm for Sn,the thermal conductivity of the system decreases exponentially while the heat storage capacity increases lineally.Moreover,when the feature size of Sn geometry is less than a critical value,which is 15 nm for 3D structure system and 25 nm for 2D structure,the Cu matrix can’t play a role in improving the effective thermal conductivity of the whole system.
基金supported by the National Natural Science Foundation of China(Grant Nos.51676122,51311140169 and 51176109)
文摘Thermal energy storage(TES) is an attention-gaining technology which is useful to improve the energy efficiency as well as to balance the energy supply and demand. Until recently, the latent heat TES(LHTES) technology has been promoted quite fast mainly due to the large heat storage/release capacity that takes place at nearly constant temperature. The phase change slurry(PCS) prepared by dispersing phase change materials(PCMs) into carrying fluid can serve not only as the energy storage media, but also as the heat transfer fluid(HTF). Compared with the conventional PCM which needs additional HTF, the PCS provides superior performance and has the great potential to upgrade the current TES systems. This paper reviews the latest investigations of the micro-encapsulated PCM(MPCM) and shape-stabilized PCM(SSPCM) slurries. A brief introduction of the preparation methods of the two types of the PCSs is summarized. And a comprehensive review of the flow and heat transfer characteristics of the PCSs, particularly in various tube-based geometries and heat exchangers, is conducted for a better understanding of the mechanism and further utilization of the next-generation TES systems.
