Preparation And Thermal Properties Of Decanoic Acid-paraffin-expanded Graphite Composite Phase Change Heat Storage Material

With the aggravation of the global energy crisis,more and more attention has been paid to the utilization and development of solar energy,but solar energy has the shortcomings of instability and intermittence.Combining phase change materials with solar energy storage technology and applying them to floor radiation heating system can effectively improve the utilization of solar energy and the temperature conditions of application environment.At present,composite phase change materials have become a research hotspot.Because the application of single phase change materials has limitations,and composite phase change materials can effectively adjust the phase change temperature,expand the application temperature range,and overcome the shortcomings of phase change leakage and low thermal conductivity,so it is of great significance to study composite phase change heat storage materials.The preparation and formability analysis of a new type of composite phase change material(CA-PW-EG)with decanoic acid,paraffin and expanded graphite(CA-PW-EG)were carried out through experiments.The main research work and conclusions of this paper are as follows:Expanded graphite was prepared by different methods,and its microstructures were analyzed by specific surface area and porosity tester and SEM(scanning electron microscopy).The results show that 32 mesh expansible graphite was expanded for 5 seconds at 900 0C,and the product is a good support material with good adsorption and thermal conductivity.The binary eutectic mixture with mass ratio of CA:PW=92.8:7.2 was prepared by melt mixing method using decanoic acid and paraffin 52 as phase change materials.The theoretical phase transition temperature was 28.96 0C.DSC(Differential Scanning Calorimeter)analysis showed that the mixture was in a low eutectic state.The melting and solidification temperatures were 30.05 and 27.41 'C,respectively.The melting and solidification enthalpies were as high as 146.53J·g-1 and 148.1398J·g-1,which were ideal phase change cores.Composite phase change materials with different decanoic acid-paraffin content were prepared by physical adsorption method.Their microstructures and phase were characterized by SEM and XRD.Their thermal storage capacity and thermal stability were tested by DSC,TG and thermal cycle test.The experimental results show that the composite phase change material with 80%decanoic acid-paraffin content has almost no phase change leakage.After 150 thermal cycles,the thermal weight loss rate is 0.69%,and the adsorption effect of expanded graphite is better.The results show that the samples with this ratio only have physical adsorption among the raw materials.The melting temperature and latent heat are 29.75? and 117.9275J·g-1,respectively.The solidification temperature and latent heat are 24.84? and 119.2193J·g-1,respectively.The samples have good thermophysical properties,and begin to lose weight at 65.32?.They have good thermal stability.After 150 thermal cycles,the reduction rates of melting and solidification latent heat were 10.26%and 7.16%respectively.The heat storage and exothermic properties experiments show that the heating and cooling rates of the composite phase change materials are 73.0%and 70.0%higher than that of the phase change cores,respectively,and the phase change rate is 86.5%higher.The thermal conductivity of the composite phase change materials is obviously improved.The formability of the composite phase change materials was analyzed.It was found that when the content of decanoic acid and paraffin was 65%,there was almost no phase change leakage in the prepared samples.After 150 thermal cycles,the weight loss rate of the sample is 0.64%,the expansion rate of diameter and thickness is 0.48%and 0.53%,respectively,which has good thermal stability.The composite phase change material with 80%decanoic acid and paraffin content was applied to floor radiant heating system.The Fluent software was used to simulate its heat storage and release performance.The results show that the composite phase change material can be heated for more than 6 hours after 8 hours,and its performance is good.