Transpiration Cooling And Waste Heat Harvesting Using Hydrogel

Modern electronics industry is both technology and energy intense.So that the electronics devices have a huge energy density during operation,and most of the energy is eventually converted into thermal energy,which makes the devices face high temperature problems.High temperature not only affects the stability of the device,but also brings safety and service life issues.Solving the high-temperature and advancing energy efficiency of electronics is critical to promote economic prosperity,energy security,and environmental protection.Some limitations of traditional strategies for heat removal on electronics make it difficult to adapt to large-scale applications or portable devices.Hydrogel is a three-dimensional network structure material with high water content,and the latent heat of water is huge.Inspired by the biological regulation of body temperature through transpiration,hydrogel can be applied to the heat dissipation of modern electronics.At present,although many researchers focusing on the temperature control for various heat sources by hydrogel,the research contents are still not comprehensive,and lacks the application of high heat flux heat source.In addition,traditional hydrogels continuously lose water,have no environmental stability,and cannot automatically replenish water.These factors cause the application of hydrogels in heat dissipation is not intelligent enough and is limited in large-scale application.Although the heat generated by modern electronic devices belongs to low-grade heat source,it will cause huge energy waste if the waste heat is not utilized due to its wide range.In considering of the problems above,the mian effort and conclusion of this work are as follows:(1)The characteristics of temperature-sensitive hydrogel to release water at the lower critical solution temperature was used to dissipate heat for virtual reality head-mounted device with high heat flux.The reliability test of hydrogel shows that it has anti-aging and anti-fatigue resistance,and has potential for practical application.The heat dissipation efficiency of the hydrogel was studied by simulation,theory and experiment.The results showed that the hydrogel could not only significantly reduce the temperature of the VR device,but also achieve efficient cooling capacity under different environmental conditions.It is clear that the fundamental reason for the excellent cooling performance of hydrogels is the phase change evaporation of water.The control mechanism of the hydrogel evaporation process and the point where the control mechanism changes are explored through experimental and theoretical research,which provides a meaningful guidance for the future electronic thermal design.(2)A self-adaptive hydrogel was designed to reduce the operating temperature and increase the energy efficiency of the device,and solved the problems of continuous water loss and inability of automatic water replenishment of traditional hydrogels.When attaching the hydrogel onto the electronics,it will absorb the heat from the electronics,and the water molecules will be released and quickly dissipate the waste heat into the ambient air.This can efficiently cool down the electronics for a better working efficiency.In the standby mode,the hydrogel can spontaneously harvest water from its surroundings to regenerate itself.The hydrogel film can be automatically cycled through temperature control and can be reused.At the same time,the internal ion concentration can be adjusted so that the evaporation rate and regeneration rate of the hydrogel reach the ideal working performance.The hydrogel was demonstrated to promote the energy efficiency of a commercial polycrystalline silicon solar cell from 14.5% to 15.5% under one sun and enhanced the maximum power of the simulated chip of a cell phone by 45% with fixed operation temperature.(3)A hydrogel with cooling,waste heat recovery and automatic regeneration capabilities is designed to solve the problem of high temperature and waste heat in electronics.The hydrogel's thermoelectric property allows it to effectively convert low-grade waste heat from a heat source into electricity.In addition,the water inside the hydrogel can evaporate freely to achieve efficient evaporative cooling.The hydrogel can also spontaneously absorb water from the surrounding air to regenerate itself.Based on these properties,the hydrogel can simultaneously heat removal via evaporative cooling and heat recovery through thermogalvanic reactions.the hydrogel film was attached to a cell phone battery during rapid discharge.It successfully decreased the temperature of the battery by 20 ~? and retrieved electricity of 5?W.The application of hydrogel to perovskite solar cell also effectively decreased the temperature of the cell at one sun and converted part of the dissipated heat into electricity.This simple,integrated,and cost-effective hydrogel has a wide range of application prospects,and provides a feasible idea for solving the contradictions of heat dissipation and low-grade thermal energy waste of electronic devices.