Numerical Investigation on Heat Transfer Characteristics of Microencapsulated Phase Change Material Slurry in a Rectangular Minichannel

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%.

Hydrodynamic Behavior of Three-Phase Airlift Loop Slurry Reactor

A novel fiber optic probe system and a set of commercial ultrasonic Doppler velocimeters have been used to study the hydrodynamic behavior of a three phase airlift loop (TPAL) slurry reactor. Experiments have been carried out in a loop reactor with 100 mm inner diameter and 2.5 m height, in which air, tap water and silica gel particles are used as the gas, liquid and solid phase, respectively. The radial profile of gas holdup, bubble size, bubble rising velocity, liquid circulating velocity, and the influence of the main operating conditions such as superficial gas velocity and solids concentration have been studied experimentally in the TPAL slurry reactor. The experimental results show that the bubble characteristics are different in various flow regimes and the radial profiles of some hydrodynamic parameters in the TPAL slurry reactor are more uniform than those in traditional three phase reactors. The distribution of the bubble size and bubble rising velocity can be described by a lognormal function. The influence of superficial gas velocity on the hydrodynamic parameters is more remarkable than that of the solids concentration.

Fundamental aspects of phase change slurries:Thermo-fluidic characteristics

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.