Plastic Crystal Neopentyl Glycol/Multiwall Carbon Nanotubes Composites for Highly Efficient Barocaloric Refrigeration System

Plastic crystal neopentyl glycol(NPG)exhibits colossal barocaloric effect with high entropy changes.However,their application is restricted in several aspects,such as low thermal conductivity,substantial supercooling effect,and poor springback properties.In this work,multi-walled carbon nanotubes(MWCNTs)with ultra-high thermal conductivity and high mechanical strength were selected for performance enhancement of NPG.The optimal mixing ratio was determined to be NPG with 3 wt%MWCNTs composites,which showed a 6K reduction in supercooling without affecting the phase change enthalpy.Subsequently,comprehensive performance of the composites with optimal mixing ratio was compared with pure NPG At 40 MPa,390J·K^(-1)·kg^(-1)change in entropy and 9.9 K change in temperature were observed.Furthermore,the minimum driving pressure required to achieve reversible barocaloric effect was reduced by 19.2%.In addition,the thermal conductivity of the composite was increased by approximately 28%,significantly reducing the heat exchange time during a barocaloric refrigeration cycle.More importantly,ultra-high pressure release rate resulted in a73.7%reduction in the springback time of the composites,offering new opportunities for the recovery of expansion work.

A Novel Asymmetric Check Microvalve for Suppressing Flow Boiling Instability in Microchannels

Flow boiling in microchannels has attracted wide attention due to its excellent heat transfer capability,but flow boiling instability is a huge challenge limiting its application.Instability can lead to a series of problems,such as uneven flow distribution,temperature and pressure drop oscillations.This work proposes a novel asymmetric check microvalve(ACMV)structure,exhibiting high ratio of resistance between the reverse and forward flow.The results show the reverse pressure drop of the ACMV structure is 2.06 times that of the forward pressure drop,and the forward flow resistance of the ACMV structure is 16%smaller than that of the conventional inlet restrictor.In addition,bubble dynamics of an isolated bubble in the generated channel under dual outlet condition was numerically investigated.It is found that the bubble grows symmetrically in the rectangular channel upstream and downstream.The distance of bubble movement downstream in the microchannel with ACMV is three times that of the microchannel with inlet restrictor.The microchannel with ACMV can suppress the backflow of isolated bubble better than microchannel with inlet restrictor.Moreover,the growth of the bubble downstream extends the effective evaporation domain,which contributes to the enhanced bubble growth rate.The ACMV is expected to be a potential replacement for the conventional inlet restrictor,which provides a novel and efficient solution for future heat dissipation from high power devices.

基于遗传算法的光伏-热电耦合系统多目标优化研究

多因素共同作用下的系统优化设计是光伏-热电耦合系统研究的难点之一。本文建立了光伏-热电耦合系统与单一光伏系统的理论模型,以最高耦合效率与相对于单一光伏系统的最大效率差值为优化目标,采用多目标遗传算法,开展了耦合系统优化设计研究。结果表明,最高耦合效率与最大效率差值两个优化目标是负相关的,且其负相关性是由光伏参考效率所导致,需综合考虑系统经济性,确定最高耦合效率和最大效率差值的折中方案,从而获得耦合系统最佳设计。