Adjustable Insulation For Enhancing The Charging And Discharging Process Of Phase Change Materials

Phase change materials have been widely used in building's envelopes and electronic devices to enable better passively thermal management of buildings or outdoor electronic devices from a variety of aspects.In general,owing to large heat capacities in the form of latent heat,phase change materials over charging and discharging cycles are able to shift nighttime cooling/daytime heating to daytime/nighttime for facilitating building passive cooling or smooth out temperature variations for alleviating temperature rise of outdoor electronic devices.To achieve above objectives,it is critical to deeply understand the effects of charging and discharging cycles of phase change materials in above applications,and develop proper structures of phase-change-material-integrated building envelopes or outdoor electronic devices for enhancing the overall performance with respect to energy conservation.Plenty of previous studies have been focused on the improved structures of the phase-change-material-involved envelopes to manage the charging or discharging process of phase change materials in a better manner.Specifically,in the applications of building energy conservation,previous studies had devoted considerable efforts to enhance the passive cooling of phase change materials during the charging process at nighttime of summer,or alleviate high solar radiation dissipation during the discharging process at daytime.However,recognizing that phase change materials typically have inherently contradictory requirements for the heat transfer rates between the external cooling/heating sources and phase change materials during the charging and discharging processes,synergetic optimization of both processes should be further addressed in depth,which is the focus of the present study.The present study proposes a dynamic control strategy of heat rates by using adjustable insulation between the phase change material layer and the ambience to improve the performance of phase change materials during both charging and discharging processes.To be specific,under the scenarios where the ambience is employed as a passive cooling or passive heating source for charging and discharging phase change materials,the thickness of an air insulation layer is dynamically controlled to adjust the thermal resistance between the phase change material and the ambience.Two application scenarios,i.e.,a roof structure with phase change materials and an outdoor photovoltaic inverter with phase change materials,are employed in the present study to show the effectiveness of the proposed adjustable insulation.The resulting heat fluxes and temperature distributions under fixed and adjustable insulation strategies are studied via a simulative approach.The results show that the adjustable insulation structure applied to the phase-change-material-integrated roof structure can effectively reduce the corresponding cooling and heating load resulting from heat gains or heat losses through the roof and reduce the corresponding energy consumption more than 20% compared to that under the fixed insulation.And the application in the phase-change-material-involved outdoor photovoltaic inverters can effectively reduce the maximum temperature rise of the device by more than 5K.To summarize,the proposed adjustable heat insulation can improve both charging and discharging efficiencies of phase change materials in buildings or outdoor electronic devices and improve the overall performance with respect to passive cooling or heating,which is shown to be a promising technology in the practical applications of phase change materials.