Phase change microcapsules can carry large amounts of heat and be dispersed into other mediums either as a solid composite or as slurry fluids without changes to their appearance or fluidity. These two standout featur...Phase change microcapsules can carry large amounts of heat and be dispersed into other mediums either as a solid composite or as slurry fluids without changes to their appearance or fluidity. These two standout features make phase change microcapsules ideal for use in thermal energy applications to enhance the efficiency of energy utilisation. This review paper includes methods used for the encapsulation of phase change materials, especially the method suitable for large scale productions, the trends of phase change microcapsule development and their use in thermal energy applications in static and dynamic conditions. The effect of phase change microcapsules on convective heat transfer through addition to thermal fluids as slurries is critically reviewed. The review highlighted that so far the phase change microcapsules used mainly have polymeric shells, which has very low thermal conductivities. Their enhancement in convective heat transfer was demonstrated in locations where the phase change material experiences phase change. The phase change results in the slurries having higher apparent local specific heat capacities and thus higher local heat transfer coefficients. Out of the phase change region, no enhancement is observed from the solid microcapsule particles due to the low specific heat capacity and thermal conductivity of the phase change microcapsules compared to that of water, which is normally used as slurry media in the test. To further the research in this area, phase change microcapsules with higher specific heat capacity, higher thermal conductivity and better shape stability need to be applied.展开更多
Microencapsulation phase change material slurry(MEPCMS) becomes a potential working fluid for cooling high energy density miniaturized components,thanks to the latent heat absorption of particles in the heat transfer ...Microencapsulation phase change material slurry(MEPCMS) becomes a potential working fluid for cooling high energy density miniaturized components,thanks to the latent heat absorption of particles in the heat transfer process.In this work,the Discrete Phase Model(DPM) based on the Euler-Lagrangian method is used to numerically investigate the convective heat transfer characteristics of MEPCMS flowing through a rectangular minichannel with constant heat flux.The results show that particles of MEPCMS are mainly subjected to drag force during the flow.Even so,they can migrate from the high-temperature region to the low-temperature region driven by the thermophoretic force,affecting the particle distribution and phase change process.Moreover,the Nux of the MEPCMS fluctuates due to particle phase change with varying specific heat capacities.Specifically,the value increases first,then decreases,and eventually increases again until it approaches the fully developed value of the pure base fluid as the particles gradually melt.Furthermore,the heat transfer performance of the MEPCMS is influenced by the combination of fluid inlet temperature fluid inlet velocity(v),and mass concentration(c_(m)) of MEPCM particles.The result shows that the maximum reduction of the maximum bottom wall temperature difference(ΔT_(w)) is 23.98% at T_(in)=293.15 K,v=0.15 m·s^(-1),c_(m)=10%.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
文摘Phase change microcapsules can carry large amounts of heat and be dispersed into other mediums either as a solid composite or as slurry fluids without changes to their appearance or fluidity. These two standout features make phase change microcapsules ideal for use in thermal energy applications to enhance the efficiency of energy utilisation. This review paper includes methods used for the encapsulation of phase change materials, especially the method suitable for large scale productions, the trends of phase change microcapsule development and their use in thermal energy applications in static and dynamic conditions. The effect of phase change microcapsules on convective heat transfer through addition to thermal fluids as slurries is critically reviewed. The review highlighted that so far the phase change microcapsules used mainly have polymeric shells, which has very low thermal conductivities. Their enhancement in convective heat transfer was demonstrated in locations where the phase change material experiences phase change. The phase change results in the slurries having higher apparent local specific heat capacities and thus higher local heat transfer coefficients. Out of the phase change region, no enhancement is observed from the solid microcapsule particles due to the low specific heat capacity and thermal conductivity of the phase change microcapsules compared to that of water, which is normally used as slurry media in the test. To further the research in this area, phase change microcapsules with higher specific heat capacity, higher thermal conductivity and better shape stability need to be applied.
基金the financial support of the National Natural Science Foundation of China (No.U20A20299)the Natural Science Foundation of Guangdong Province (No.2019A1515012119)。
文摘Microencapsulation phase change material slurry(MEPCMS) becomes a potential working fluid for cooling high energy density miniaturized components,thanks to the latent heat absorption of particles in the heat transfer process.In this work,the Discrete Phase Model(DPM) based on the Euler-Lagrangian method is used to numerically investigate the convective heat transfer characteristics of MEPCMS flowing through a rectangular minichannel with constant heat flux.The results show that particles of MEPCMS are mainly subjected to drag force during the flow.Even so,they can migrate from the high-temperature region to the low-temperature region driven by the thermophoretic force,affecting the particle distribution and phase change process.Moreover,the Nux of the MEPCMS fluctuates due to particle phase change with varying specific heat capacities.Specifically,the value increases first,then decreases,and eventually increases again until it approaches the fully developed value of the pure base fluid as the particles gradually melt.Furthermore,the heat transfer performance of the MEPCMS is influenced by the combination of fluid inlet temperature fluid inlet velocity(v),and mass concentration(c_(m)) of MEPCM particles.The result shows that the maximum reduction of the maximum bottom wall temperature difference(ΔT_(w)) is 23.98% at T_(in)=293.15 K,v=0.15 m·s^(-1),c_(m)=10%.
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.
