Preparation Of Phase-Change Paraffin Emulsion And The Mechanism Of Subcooling

Phase change paraffin emulsion is a novel multi-functional fluid,which has the ability to store and transfer heat simultaneously.It has potential applications in various industries,such as the storage of solar energy and recovery of industrial waste heat.However,the application of phase change paraffin emulsion suffers from undercooling phenomenon,which reduces the ability of phase change paraffin emulsion to store and transfer heat remarkably.In order to reveal the mechanism of subcooling and to study the preparation method of the paraffin emulsion without subcooling,suitable surfactants and co-surfactants were selected in this work to prepare phase change paraffin emulsions with different particle sizes at certain emulsification temperature and stirring speed.The particle size distribution and particle size of paraffin emulsions were measured with a Malvern laser particle size analyzer;the morphology of the droplets of paraffin emulsions was observed by scanning electron microscopy?SEM?and transmission electron microscopy?TEM?;the stability of paraffin emulsions was evaluated by an all-round stability analyzer.;the rheological measurements were performed by a rheometer;and the thermodynamic properties,including melting point,freezing point and enthalpy value,were measured using a differential scanning calorimeter.The experimental results were as follows:?1?The phase change paraffin emulsion was prepared by the phase transformation method,in which paraffin wax was used as the oil phase,Span-80 and Tween-80 as the compound emulsifier,and n-butanol as the co-emulsifier.During the preparation,the contents of paraffin wax and n-butanol were constant at 10 wt.%and 2.0 wt.%respectively while the different emulsifier contents of 3.0,4.0,5.0,6.0 and 7.0 wt.%were employed with a certain mass ratio of Span-80 to Tween-80 equal to 7:8.The emulsification temperature of 80 ?,stirring speed of 1000 rpm and emulsification time of 40 min were used.Stabilized paraffin emulsions with average particle sizes of 330,257,217,173 and 147 nm were obtained finally.And the resulting emulsions exhibited a shear thinning behavior of non-Newtonian fluid and good flowability.?2?The DSC results showed that subcooling phenomenon appeared apparently with the decrease in temperature of the phase change paraffin emulsion.The subcooling degree of paraffin emulsions increased linearly with increasing cooling rate.There was no significant difference in inherent subcooling degree of phase change paraffin emulsions with different particle sizes,which was approximately 15.0 ?.The reason for the subcooling phenomenon which the crystallization of the paraffin in the emulsion is mainly based on homogeneous nucleation.?3?The subcooling of phase change paraffin emulsions can be effectively inhibited by introducing solid particles and inducing paraffin crystallization in heterogeneous nucleation.The stable Paraffin Pickering Emulsion without subcooling phenomenon was prepared by mechanical stirring method and[Mg₆Al₂?OH?_i6CO₃]·4H₂O?MAH?emulsifier.The viscosity of the emulsion was moderate.Three parameters of oil-water ratio,content of MAH and agitation rate were optimized with orthogonal experimental design.The optimal preparation process was selected.The results revealed that the best ratio of oil-water was 1:8,the best content of MAH was 4.0 wt.%and the best stirring rate was 6000 rpm.