Research On Microencapsulation Of Paraffin Based Core With Calcium Carbonate Shell For Temperature Regulation And Heat Transfer Enhancement

New energy vehicles have been developed rapidly as the pressure of energy and environment crisis,thereinto power battery thermal management become a key problem need to be solved.Phase change materials(PCM)is one of the best thermal control technologies as its high latent heat and small temperature changes during a phase change.PCM can absorb/release heat when the battery temperature is too high/low,which helps maintain battery temperature within a safe range.However,PCM suffer leakage during the melting process and poor in heat transfer,which largely restricts their further applications.Hence,encapsulation and heat transfer enhancement of PCM are vital for the battery thermal management system.In this paper,novel PCM with improved thermal stability,temperature regulatory and thermal conductivity is developed,the mechanism of temperature regulatory and heat transfer enhancement are studied as well.1.RT42 paraffin is encapsulated by calcium carbonate shell and its thermo-physical properties are analyzed.The results show that the thermal stability and thermal conductivity of the microencapsulated phase change materials(MEPCM)are improved due to the presence of calcium carbonate shell.The as-prepared MEPCM have a spindle morphology and compact surfaces with diameter ranging from 1 to 6 ?m,the latent heat is 143.6 J/g when phase change occurred at 48 °C.Besides,the thermal conductivity of the microcapsules was enhanced by 2.06~2.92 times compared to the pure paraffin.Since the low costs and outstanding properties of MEPCM,it exhibits a good prospect when assisted in battery thermal management.2.Novel microencapsulated phase change materials with calcium carbonate shell and paraffin-based binary cores were prepared via self-assembly method.The phase change temperature of the microcapsules could be adjusted from 20 to 48 °C by changing the weight ratio of binary cores.The thermal conductivity of the microcapsules was enhanced by 2.25~2.54 times compared to the pure paraffin.Besides,mass loss of the microcapsules was between 5% and 28% when heated to 400 °C.Hence,it could broaden the phase change temperature range effectively,which is advantageous to low temperature starting and high temperature cooling of battery.3.Different mass fractions of flaked graphite(FG),expanded graphite(EG)and graphite nanosheets(GNS)as heat transfer promoter were added in the MEPCM respectively.The phase change composites(PCC)with double-layer network possess enhanced thermal conductivity and thermal stability.The influences of graphite additives morphology and size on thermal conductivity are analyzed comparatively.The influencing factors of the thermal conductivity and thermal conductive network forming conditions are explored.As a result,a carbon network structure in PCC was observed with 20wt%,20wt% and 5wt% of FG,EG and GNS respectively.The corresponding thermal conductivities was increased up to 4.31 times,20.23 times and 69.95 times of the pristine paraffin,when the contents of graphite packing are 20wt%.Therefore,the significant enhancement on thermal properties of the PCC is a promising and effective route to reduce the risk of thermal runaway of power battery.4.An effective modified model based on the thermal conductivity of MEPCM/EG composites was presented.The theoretical results agree well with the experiments and the average deviation is only 9.6%.The results suggest that the modified theoretical model proposed in this study is simple and with high accuracy,which can largely save the time and cost.So it can be generalized to predict the effective thermal conductivity of such kind of MEPCM based composites.