Research On The Heat Transfer And Thermal Control Performance Of Paraffin Phase Change Material

The continuous increase in energy demand and low energy efficiency make the shortageof energy supply. In order to increase the energy efficiency and protect the environment, heatstorage technology was used to solve those energy problemse. Paraffin has a high thermalenenry density with a nearly isothermal operation temperature. However, its thermalconductivity is low, and its traditional packing will lead to form a solid film on the containerwall in the solidification process of the phase change materials, which increases the theramalresistance and reduces the heat transfer rate of the device. Hence, these devices with paraffinphase change materials will be costly and heavy and their application is limited.To overcome these disadvantaes of paraffin, a paraffin with appropriate phase-changetemperature was select as phase change material and the expanded graphite (EG) was selectedas the inorganic supporting material. Paraffin/expanded graphite composite phase changematerials were prepared by the physical adsorption method. The composite phase changematerials were characterized by different scanning calorimeter (DSC), scanning electronicmicroscope (SEM), polarization optical microscope (POM), Hot Disk thermal analysiser andthermocycling experiment. The results show that the shape-stabilized phase change materialshave form-stable, high thermal conductivity and heat heat storage capacity, excellent thermalstability and service life.The shape-stabilized phase change materials that containing80%of paraffin was chosento be placed on the simulative chip directly. The temperature variations of the simulative chipsurface under constant heating power and ON/OFF duty cycle were measured to investigatethe cooling performance of the simulative chip with shape-stabilized phase change materials.At the same time, the impacts of composite PCM dosage (thickness) and environmenttemperature on the performance of simulative chip were also studied. The experimentalresults show that the chip with shape-stabilized PCM has better performace of heat dissipationand resistance to heat shock than the origin one at the same conditions. It can efectivelyreduce the temperature rise rate and range of the simulative chip surface and extend the timeof thermal control.The Fluent software was used to simulate the melting process of phase change material,the results proved that the natural convection in the melting process of paraffin can’t beignored. The coupled calculation model of a VOF sub-model with an enthalpy-porousmedium one can completely reflect the characteristics of paraffin in various aspects during its phase change. The apparent heat capacity and the enthalpy-porous medium was respectivelyused to simulate the melting of shape-stabilized PCMs, the results show that they areconsistent, in other words, the apparent heat capacity can replace the enthalpy-porous mediumunder certain conditions.