| Phase change materials?PCMs?can achieve energy storage and release through the endothermic and exothermic behavior in the process of transformation.They can improve energy utilization and reduce waste heat losses so that it has been widely applied in solar energy development,waste heat recovery,refrigeration and so on.Ionic liquids?ILs?is a chemical substance composed of pure ions.It has many singular properties,which is one of the hot target in the field of organic chemistry.In this paper,a series of two element composite phase change energy storage system has been obtained through compound which use organic matter as raw material,while ionic liquid as the additive.Based on the investigation of its phase transition properties,the influence of ionic liquids on thermal properties of organic phase change materials was preliminarily studied,and possible mechanisms were discussed.We were choosed lactate acid and simple amine as raw material,lactate acid ionic liquid were synthesized by one-step method,and selected the myristic acid as the organic phase change material,propylamine lactate-myristic acid?PM?,octylamine lactate-myristic acid?OM?,laurylamine lactate-myristic acid?LM?composite phase change energy storage system were obtained through heating and mechanical mixing method,the performance of which were characterized and analyzed by DSC and thermal conductivity test.The main work were as follows:?1?In PM,its the phase change temperature and latent heat were decreased,the mass ratio of propylamine lactate were increased 1%will caused 0.21?decreased of the phase change temperature and 3.01 J/g decrease of latent heat.The undercooling variation was not obvious,the maximum value could reached 5.4?,the minimum value of 2.6?.Overall,propylamine lactate makes the undercooling of system increased.When the myristic acid compound 40%propylamine lactate,system of heat conduction coefficient reaches the maximum value of 0.2711 W·m-1·K-1,13%higher than myristic acid.After200 thermal cycles,the thermal properties of propylamine lactate-myristic acid composite system could be preserved to some extent,but when the mass ratio of more than 20%,the thermal stability were poor.?2?In OM,when the average mass ratio of octylamine lactate and myristic acid were increased 1%,the phase changen temperature of the system would reduced by 0.23?,and the latent heat of phase change were reduced by 3.61 J/g.When the quality of octylamine lactate with myristic acid ratio was 2.5%,the melting point of myristic acid increased from52.0 to 58.7?.According to the analysis of infrared spectrum and X ray diffraction,it was suggested that the new phase formed.And when Octylamine lactate with myristic acid in the mass ratio of 7.5%,10%,15%,25%,the undercooling of myristic acid were decreased,the minimum value of 2.0?.Adding trioctylamine lactate increased the overall thermal conductivity of the system,when the quality of octylamine lactate with myristic acid ratio were 30%,the thermal conductivity of OM were reached the maximum value of 0.2520W·m-1·K-1.But when the mass ratio achieved 40%,the thermal conductivity of OM were0.2284 W·m-1·K-1,lower than that of myristic acid,which proved that octylamine lactate has made the thermal conductivity of OM reduction.When the mass fraction of Octylamine lactate were less than 7.5%,the thermal stability proved to be good,whose thermal properties of the system were almost no change after 200 cycles of thermal cycling.?3?In LM,the mass ratio of laurylamine lactate lactate were increased 1%will led0.25?decreased of the phase change temperature and 2.32 J/g decreased of latent heat.When laurylamine lactate with myristic acid in the mass ratio of 10%?15%?25%?30%,the undercooling of myristic acid were decreased,the minimum value of 2.0?.It may be related to that the undercooling of laurylamine lactate is low.There were an irregular relationship between the thermal conductivity of the LM and the mass fraction of laurylamine lactate,the maximum value is 0.2657 W·m-1·K-1,the minimum was only0.2301 W·m-1·K-1.In addition,LM exist phase separation phenomena during solidification,resulted in the existence of a significant mismatch between the melting heat and heat of solidification,which were more than 50 J/g.After many thermal cycles,there were great change with latent heat of LM and the application value of it were relatively small.?4?In the three systems,with the increased of the mass fraction of ionic liquids,the phase change temperature and the decrease rate of the latent heat:LM>OM>PM.The effect of reduce undercooling:PM were the largest,and OM and LM just approximately equal.In the enhancement of thermal conductivity,the heat conduction of myristic acid were increased by PM as a whole,and both OM and LM will led to the decreased of thermal conductivity.In terms of thermal stability,PM and OM were the same,LM had phase separation so that its thermal stability were poor.This reflects the effect of the chain length of the ionic liquid cation on the thermal physical property of the system. |
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