Phase Change Mechanism And Thermal Properties Of Stearic Acid Based PCM

Phase change energy storage technology has been widely used in social communication,construction,textile and other fields,because of its high energy storage density,high flexibility,low cost,easy to promote,and as a result,the development and study of phase change materials has become a hot research topic in the field of energy.However,the current study of phase change materials work mainly focused on the ascension of thermal performance and the improvement of engineering properties,but the phase transformation mechanism study is very little and a heated controversy existing..This paper mainly study the soild-liquid phase transformation mechanism of stearic acid by means of variable-temperature FT-IR spectroscopy and ultraviolet-visible absorption spectra(UV-Vis)with stearic acid as the research object.We first put forward the phase transition mechanism of stearic acid combining previous research results to,then,,qualitative pointed out the source of stearic acid phase change latent heat according to the phase transformation mechanism proposed in this paper;lastly,put forward two ways to improve stearic acid phase change latent heat based on the correctness of the proposed mechanism and it is proved by the result of experiment.This paper mainly includes the following aspects.Firstly,we tested the variable temperature FT-IR and UV-VIS spectrum of stearic acid before and after phase change in order to analysis the molecular structure change,accordingly speculated that phase transformation mechanism is as follows: there are three kinds of dimmers exists in the stearic acid solid,and the methylene exists as all-trans conformation;When heating temperature to melt point,alkyl chain conformation became to linear chain,and the proportion of three kinds of dimers in stearic acid has changed;carboxyl dimers double hydrogen bond is weakened in the process of transformation,besides.So,stearic acid phase change latent heat derived from the rollover of alkyl chain conformation,dispersion force between methyl and methylene,the weakened of hydrogen bond on carboxyl dimmers.Secondly,SA/alpha-CNTs composite phase change materials was prepared,in considerision of the high thermal conductivity properties of carbon nanotubes,it can be used to improve the thermal conductivity of SA,what's more,the polarity of carboxyl distribution in carbon nano tube wall is contribute to reshape the SA molecular arrangement,FT-IR spectrum test comfirmed the modification mechanism we proposed.Performance test results show that the SA/?-CNTs materials thermal conductivity performance improved significantly,phase change temperature decreased 5 ? and phase change latent heat increaseed nearly 10%;SA/?-CNTs/PMMA phase change microcapsules is preparated by in-situ polymerization method with SA/?-CNTs composite material as the core material and the methyl methacrylate(MMA)as shell material.SEM and TEM images show that the microstructure of the material showing spherical connected by carbon nanotube,verify test scanning calorimeter(DSC)show that the phase change latent heat of 125J/g,and phase transition temperature reduced to 50 ?,which satisfy the applications of room temperature,the thermal decomposition temperature increasesed nearly 30 ?,promoting its engineering properties.Thirdly,we preparated SA/PEG binary organic phase change system in melt-biending method,the results of FT-IR spectra of test show that in the SA/PEG system,a fourth existing status SA molecules was occured in the phase transformation process,HNMR and UV spectrum further verifiedour judgment of SA/PEG molecular structure;The melt-point of SA/PEG treated by hexadecafluoro-heptan,and the phase change latent heat have a 8% ascension.We also found that the pretreatment of perfluorinated-heptane is good for euutectic crystallization.Cooling curve results show that the SA/PEG material behave better than SA on temperature control performance.