Thermochemistry Of Organic Phase Change Materials For Thermal Energy Storage

Thermal energy storage are the technologies that make use of latentheat stored by Phase Change Materials (PCMs). They can reshape patternsof electricity use for day and night. And they can make a full use of solarenergy and are environment-friendly. In this paper, based on the performances evaluation of cool storagemedia PCM, unitary fatty alcohols PCMs are chosen as experimentalobjects. Those performances, such as phase change temperature,super-cooling degree, transition heat and thermal stability of PCMs wereinvestigated. Firstly, on the basis of phase change temperature, six mixtures fromunitary fatty alcohols are obtained, whose temperatures are during 7to 10℃. They are considered appropriate PCMs for cooling application. What'smore, 1-octadecanol for heating application also is attained. Secondly, thetransition heat of PCMs is analyzed using Differential ScanningCalorimeter. The heat of mixtures is smaller than that of the average offatty alcohols, and the former is about 20%of the later. But the transition IV北京化工大学硕士研究生毕业论文heat of 1-octadecanol is large, with 242.85 J·g-1. So it can be used forheating application. About thermal stability, the mixture of 1-decanol and 1-hexadecanolare studied. The deviations of the freezing point and the transition heatfrom the mixture are 0.72% and 0.68% through 50 cooling and heatingcycles. The above results manifest that fatty alcohol PCM has good thermalstability. The organic PCM thermal conductivity is considered low for theapplication of thermal energy storage. So, in this paper, the thermalconductivities character of paraffin 54# with additives are investigatedusing thermal analysis kinetics. The model of Avrami is chosen to describethe crystal process of paraffin 54#. At the temperature of 44℃, the rateconstant of crystallization is calculated as 0.117×10-4min-1. Carbon fiber,electric polymer and nano-sized magnesium hydroxide are added toparaffin respectively, however the results show they are not suitable.Finally, copper wires and aluminum powders are used to improve thethermal conductivities. Compared with the initial rate constant ofcrystallization, it can be confirmed that the both additives are valid. Therate constants of crystallization get larger, with 0.138×10-4min-1 and0.154×10-4min-1, improve by 17.95% and 31.62%, respectively. The resultsshow that copper wires and aluminium powders provide the effectiveadditives in the paraffin.