Determination Of Phase Change Temperature Range And Latent Heat Based On T-history

Phase change materials can absorb or release a large amount of heat in a small temperature range and have the function of storing energy and controling temperature.The most important properties of the phase change materials are latent heat and phase change temperature range.This paper focuses on the determination of latent heat and phase change temperature range,Capric acid,octadecane,the compounds calcium chloride hexyhydrate(YP-24)and paraffin wax were choosen as tested materials.They represented single molecule organic substances existing or not existing supercooling.salt hydrate and polymolecular organic phase change materials.respectively.The temperature-time curves of phase change materials were obtained based on T-history,meanwhile,the cutting points were selected through the first and second derivatives of temperature and the phase change temperatue ranges were determined by tangent method.During cooling,the temperature curves of capric acid,octadecane and paraffin existed the inflection point,the minimum value point of the first derivative and the max point of second derivative,and the temperature curves of YP-24 existed supercooling,During heating,the temperature curves of capric acid and octadecane existed the second derivative of minimum value point and inflexion point and the maximum value point of the first derivative,and the temperature curves of YP-24 and paraffin existed the maximum value point of the first derivative and inflexion point and reference point.The phase change temperature ranges of capric acid,octadecane,YP-24,and paraff-in wax were tested by modified T-history method,the results show that the cry'stallization ranges were 31-29?,29-26?,20-24-22?,27-23?,and the melting range were 29-32?,27-30?,22-27?,22-27?,respectively.Their enthalpy-temperature curves were obtained and can reflect the supercooling of octadecane and YP-24.The enthalpies of four kinds of materials were obtained by enthalpy-temperature curves and temperature change ranges.The crystallization enthalpy of capric acid,octadecane,YP-24,paraffin wax were 179.1 J/g.200,1 J/g,140.9 J/g and 135.6 J/g,and the melting enthalpy were 169 J/g,205,9 J/g.145 J/g and 112,8 J/g,respectively.The standard rates of both crystallization and melting enthalpy were less than 10%.Introduced 12.6 J/(g·?)as threshold of heat capacity,equivalent specific heat of tested materials on special temperature range was higher than threshold during either cooing or heating.Modified T-history method can be used to test the phase change temperature range and enthalpy.In order to verify modified T-history method,the phase change temperature ranges and enthalpies of decanoic acid,octadecane,YP-24 and paraffin wax were tested by DSC.The crystallization temperature ranges of capric acid,octadecane.YP-24,paraffin wax were 28-27?.28-27?,21-17?,26-22? and the melting temperature range were 31-33?,28-30?,22-26? and 23-28?,respectively.Phase change temperature ranges tested by modified T-history method were broader than that of DSC.The crystallization enthalpies of capric acid,octadecane,YP-24,paraffin wax tested by DSC were 161.2 J/g,234.2 J/g,116.1 J/g and 108.9 J/g,and the melting enthalpies of capric acid,octadecane,YP-24,paraffin wax tested by DSC were 158.5 J/g,225 J/g,07 J/g and 110.2 J/g,respectively.The enthalpies tested by modified T-history method were higher than that of DSC except octadecane.The effect of testing volume reflected in broader phase change temperature range and higherenthalpy.The effect of the mass fraction of CaCl2,SrCl2·6H2O and Nano-SiO2 on supercooling and energy storage of CaCl2·6H2O was studied by T-history method and orthogonal analysis.The results showed that the effect of CaCl2·6H2O mass fraction on supercooling degree and energy storage is larger than nano-SiO2 and SrCl2·6H2O.