Papers by Keyword: Phase Change Temperature

Abstract: Temperature and enthalpy of phase changes taking place in PCM (Phase Change Material)-modified plasters within their heating and cooling exposure are studied in the paper. The studied plasters are composed of hydrated lime, pozzolan admixture, silica sand, water, and encapsulated parrafinic wax that is used as PCM. The studied materials are characterized by bulk density, matrix density, and total open porosity. The temperature of phase changes, heat of fusion and crystallization are evaluated by DSC (Difference Scanning Calorimetry) analysis that is performed in inert nitrogen atmosphere. Experimental data reveal a substantial improvement of heat storage capacity of PCM-modified plasters as compared to the reference material without PCM.

Abstract: This paper investigated the thermal performance of shape stabilized phase change paraffin and shape-stabilized phase change fatty acid. And the PCMs are mixtures of 60% 46# paraffin and 40% liquid paraffin, 65 % 48# paraffin and 35% liquid paraffin,30%capric acid and 70% lauric acid, 30%capric acid and 70% myristic acid. Support material is high-density polyethylene. The results in this paper show that: Thermal stability of both of the two types of phase change materials are good, thermal stability of shape stabilized phase change fatty acid is better than that of paraffin. Results in this paper can provide references and basis for the application of phase change material walls in the practice building.

Abstract: The problems such as poor oxidation resistant properties at high temperatures and abated thermal storage capacities after repeated thermal cycles still exist in heat storage alloys. In order to alleviate these problems, orthogonal experiment was used to design nine Al-Si-Mg-Cu alloys in this work. An SII TG/DTA6300 differential thermal analyzer was used to determine the heat storage properties of these alloys. After integrating a series of factors, Al-12Si-2Mg-15Cu alloy was selected as the heat storage alloy. The oxidation test of this alloy at the temperature of 650 °C for 300 h was carried out, and the oxidation kinetics curve was obtained. The results showed that the oxide film was of good protection. This alloy exhibited a good thermal stability in view of the latent heat of fusion decreased 3.53%, the initial phase transition temperature decreased 0.1 °C, and terminated phase transition temperature increased 3.1 °C after 150 times of thermal cycles. The photomicrograph was used to discuss the reasons of the performance changes of this alloy.

Abstract: Paraffin and modified inorganic porous materials composites as phase change energy storage materials were prepared by absorbing paraffin in porous network of inorganic materials. In composite materials, paraffin was used as phase change material (PCM) for thermal energy storage, and γ-Al2O3 acted as supporting material, ethanol was solvent. A series of characterization were conducted to analyse and test the performance of the composite materials, and differential scanning calorimeter (DSC) results showed that the PCM-3 composite has the melting latent heat of 115.9 kJ/kg with melting temperature of 63.0°C. Due to the capillary and surface tension forces between paraffin and γ-Al2O3, the leakage of melted paraffin from the composites can be prevented. Several kinds of paraffin mixtures were also studied by adsorbing into the supporting materials, so that the composite energy storage materials with different phase change temperature can be used in the building wall to storage thermal of different regions. In a word, the paraffin/γ-Al2O3 composites have a good thermal stability and can be used repeatedly.

Abstract: Nano-aluminum, which has high thermal conductivity and good compatibility, was added into paraffin to improve its thermal conductivity. Surface modified technology was adopted and dispersant was used to prepare uniform and stable organic phase-change nano-fluid of paraffin and nano-aluminum. Experiments were conducted to test the phase-change temperature and latent heat of the prepared organic phase-change nano-fluid. Results show that the addition of nano-aluminum has no effect on phase-change temperature, but it changes phase-change latent heat of the prepared organic phase-change nano-fluid. Reduced degree of the latent heat is nearly proportional to the quantity of the added nano-aluminum.

Abstract: Ice storage system that water is used as low temperature latent heat storage material, refrigerator capacity is increased and COP is decreased because refrigerator is operated at low temperature due to supercooling of water in the course of phase change from solid to liquid. This study is investigated the cooling characteristics of the TMA-water clathrate compound including TMA (Tri-methyl-amine, (CH3)3N) of 20~25 wt% as a low temperature latent heat storage material at -5°C, cooling source temperature. The results showed that the phase change temperature, the specific heat is increased and the supercooling degree is decreased as the weight concentration of TMA became higher. Especially, low temperature latent heat storage material containing TMA 25 wt% has the average of phase change temperature of 5.8°C, supercooling degree of 8.0°C and specific heat of 4.099kJ/kgK in the cooling process. Phase change temperature higher than that of water and inhibitory effect against supercooling can be confirmed through experimental study on cooling characteristics of TMA-water clathrate compound.

Abstract: This study aims to find out cooling characteristics of TMA 25wt%-water clathrate compound with ethanol such as supercooling, phase change temperature and specific heat. For this purpose, ethanol is added as per weight concentration and cooling experiment is performed at -6
, -7
and -8
, cooling heat source temperature, and it leads the following result. (1) Phase change temperature is decreased due to freezing point depression phenomenon. Especially, it is minimized as 5.1
and 5.0, 3.8
according to cooling source temperature in case that 0.5wt% of ethanol is added. (2) If 0.5wt% of ethanol is added, average supercooling degree is 0.9
and minimum supercooling is 0.8, 0.7
according to cooling heat source temperature. The restraint effect of supercooling is shown. (3) Specific heat shows tendency to decrease if ethanol is added. It is 3.013~3.048 kJ/kgK according to cooling heat source temperature if 0.5wt% of ethanol is added. Phase change temperature higher than that of water and inhibitory effect against supercooling can be confirmed through experimental study on cooling characteristics of TMA 25wt%-water clathrate compound by adding additive, ethanol.