Papers by Keyword: Supercooling

Abstract: In its use, reefer containers require a lot of energy to operate to cool the cargo inside. Because the cooling system in the reefer container must operate continuously to maintain the temperature in the container. To reduce the operation of the cooling system, reefer containers are equipped with PCM (phase change material) as thermal energy storage which can store heat energy longer to create a lag time for the operation of the cooling system. In previous research, the use of PCM in cold storage can save the cost of using cold storage. From this research, the use of PCM in reefer containers was developed. The eutectic mixture used as PCM is NaCl-H2O with additional ingredients is propylene glycol. Before being applied to the reefer container, the mixture was tested using the cooling chamber methods to determine its thermophysics. The presence of additives in the PCM eutectic mixture is expected to reduce the supercooling phenomenon, reduce corrosive properties and increase the use of PCM based on NaCl-H2O.

Abstract: It is reported actual volume fraction of the primary phase in alloys is larger than the equilibrium value. Larger volume fraction of the primary phase may cause shrinkage cavities and surface or internal cracks. Although control of the solidified structure is important for the quality of cast products, this problem has not been fully elucidated. Taking these results into account, this study has been carried out in order to comprehend the phenomenon of larger volume fraction of primary phase. The Sn-Pb alloy has been used as a test alloy to examine the relation between supercooling for nucleation and the volume fraction of primary phase. Actually, the volume fraction of the primary phase in Sn-Pb alloy is larger than that of the lever rule. It was also observed that the volume fraction of β-Sn decreases with decreasing the supercooling in the early stage of solidification. In the final stage of solidification, however, the effect of supercooling on volume fraction of primary phase is small. Futhermore, when the supercooling was low, the volume fraction of primary phase slowly increased.

Abstract: The method of perturbed angular correlation (PAC) was used to determine lattice locations of ¹¹¹In impurity probe atoms present in extreme dilution in the intermetallic compound FeGa₃. In slightly Ga-poor samples, probes were found to strongly prefer one of two inequivalent Ga-sites. In slightly Ga-rich samples at room temperature, 293 K, the PAC spectrum exhibited an unperturbed quadrupole interaction signal that is consistent with indium probes dissolved in small liquid pools of the excess Ga. A myriad of such pools are probably located along grain boundaries in the sample. Cooling from 293 K down to 12 K, the site fraction of indium in liquid decreased, being offset by the increase in a signal attributed to indium solutes in precipitates with other impurities at the sides of the Ga pools. However, these changes were completely reversible upon heating, and no crystallization of the liquid gallium pools was observed down to 12 K. This is attributed to the extraordinarily small volumes for the pools, which, while not measured directly, are orders of magnitude smaller than cubic microns. The measured temperature dependence of the site fraction of indium in the liquid was used to extend the metastable solubility curve for indium in liquid gallium down to a temperature of 150 K, much lower than the eutectic temperature of Ga-In at 288.5 K.

Abstract: The dehydration kinetics of phase change material KAl(SO₄)₂•12H₂O was studied under non-isothermal conditions and the Kissinger’s method was applied to analyze the TG and DSC data in order to calculation of activation energies and pre-exponential factors for different heating rates. It was concluded that dehydration of KAl(SO₄)₂•12H₂O occurred in three steps. The activation energies and pre-exponential factors were calculated as 95.9 kJ/mol and 1.95×1010min-1 for step I, 128.8kJ/mol and 3.67×1012 min-1 for step II, 159.6kJ/mol and1.92×1013min-1 for step III, respectively. In addition, various materials have been tested to prevent the KAl(SO₄)₂•12H₂O supercooling.

Abstract: Inorganic salt hydrates as a new type of clean and renewable energy storage materials are widely used in a variety of fields due to their high volumetric latent storage density. However, the supercooling and phase separation effects limit their applications. In this paper, the characteristics of inorganic salt hydrates as PCMs were introduced, and the supercooling and phase separation for inorganic salt hydrates as PCMs were summarized in details. Then, some new approaches of nucleating and thickening agents to overcome the supercooling and phase separation were presented. Finally, the prospects and new trends of salt hydrates as PCMs in the future were also demonstrated.

Abstract: Magnesium chloride hexahydrate (MgCl2•6H2O), which has a melting temperature of 389.7 K and latent heat of 168.6 kJ/kg, is one of the cheapest materials used as the thermal energy storage material. Like most hydrated salts, MgCl2•6H2O also has the problems of supercooling and phase segregation to limit its application. In this paper, some new progresses on magnesium chloride hexahydrate as phase change materials are summarized, and the new trend in the future is pointed out.

Abstract: Traditional casting usually solidifies one homogeneous liquid by removing heat from liquid surface, by which the microstructure solely depends on the heat removal rate for the given alloy composition. The newly developed two-liquid composite simultaneous casting concept raises an alternative to control microstructure. The concept introduces the solidification while mixing technique so that the microstructure depends not only on the heat-removing from liquid surface but also the heat transfer from one liquid to another. The paper reports the experimental validation of the concept by two-liquid casting of Sn-Pb alloys. Reduced grain size, increased microhardness, rougher and more fractal grain surfaces are observed for the alloy solidified by two-liquid casting in comparison of the microstructure obtained by conventional solidification techniques.

Abstract: Directional solidification technique permits materials to grow along specific orientation, in order to obtain mechanical and/or physical anisotropy. The present research attempts to introduce the research work in the field of processing of some advanced materials by innovative directional solidification techniques performed at State Key Laboratory of Solidification Processing and with author’s intended research work. The paper deals with the specific topics on state of the art of directional solidification: single crystal superalloy and Nd-Fe-B alloys under high thermal gradient, Cu-Ni alloys under deep supercooling of the melt. The relevant solidification phenomena, such as morphological evolution, crystal growth for multi-phases in the processing of directional solidification, are discussed briefly. The trends of developments of directional solidification techniques are also prospected.

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.