• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.2
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• pp.189-199
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• 2000

This paper investigates the thermodynamic performance of latent heat thermal energy storage system using two phase change materials(2-PCM system). The thermodynamic merit of using 2-PCM is clear in terms of exergetic efficiency, which is substantially higher than that of 1-PCM system. Optimum phase change temperature to maximize the exergetic efficiency exists for each case. The heat transfer area ratio of high temperature storage unit, X, becomes another important parameter for 2-PCM system if the phase change temperatures of given materials are different from those of optimum conditions. It is a good approximation for X$_{opt}$ to be 0.5 when optimum phase change temperatures are used. Otherwise X$_{opt}$ is determined differently as a function of given phase change temperatures.res.

• Resources Recycling
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• v.8 no.1
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• pp.23-28
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• 1999

Firing characteristics, transverse rupture strength, and heat capacity were studied of the heat-reservoir refractory materials made of red-firing clay, mill scale, and water glass. The firing shrinkage increased with increase of the clay proportion in samples. The volume of fired bodies showed shrinkage by drying up to $300^{\circ}C$, steady expansion in the 300-$700^{\circ}C$ range due to phase transition of iron oxides. and drastic expansion above $1200^{\circ}C$. Flexural strength decreased from 5.6 Mpa to 2.35 Mpa with the decrease of the ratio of clay to mill scale from 1:1 to 1:3 Heat capacities changed from 1.1 Joul/g$^{\circ}$C to 1.35 Joul/g$^{\circ}$C with the ratio of millscale to clay ratio from 1:1 to 1:3. Mill scale in the specimen appears to exist as liquid phase during firing. Firing the specimens in air leads to the eruption of the molten mill scale to the sample surfaces. Contrarily, firing samples in a refractory sagger with a cover suppressed the eruption of the molten mill scale to the surfaces. The addition of mill scale gave rise to porous sintered bodies which would delay cooling rates of heat-reservoir brick.

• Journal of Energy Engineering
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• v.5 no.2
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• pp.115-122
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• 1996

Heat transfer characteristics of low temperature latent heat storage systems have been examined for the circular finned and unfinned tubes using Na$_2$B$_4$O$\_$7/10H$_2$O as a phase change material. In order to reduce the supercooling of PCM, 3 wt% of Na$_2$B$_4$O$\_$7/10H$_2$O was added as the nucleating agent and 2.2 wt% of acrylic acid sodium sulfate was used as the thickener. The heat storage vessel has dimension of 530 mm height, 74 mm 1.D. and inner heat transfer tube is 480 mm height and 13.5 mm O.D. Water was employed as the heat transfer fluid. During the heat recovery experiment, the heat recovery rate was affected by the flow rates and inlet temperature of heat transfer fluid. The enhancement of heat transfer by fins over the unfinned tube system was found to be negligible in the thin finned tube systems, whereas the heat transfer coefficient in the thick finned tube system is approximately 60% higher than that in the unfinned lobe system. The experimentally determined heat transfer coefficient for the unfinned tube and thick finned tube systems are 150-260 W/㎡$^{\circ}C$ and 230-530 W/㎡$^{\circ}C$, respectively. The fin efficiency based on the heat transfer coefficient and area increased by fins was found to be 0.05 and 0.26 for the thin and the thick finned tube systems.

• Journal of Energy Engineering
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• v.8 no.2
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• pp.224-232
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• 1999

Latent heat storage system using micro-encapsuled phase change material is effective method for floor heating of house and building. The temperature profile in capsule block and flow rate of hot water are important parameters for the development of heat storage system. In the present study, a mathematical model based on 3-D, non-steady state, Navier-Stokes equations, scalar conservation equations and turbulence model ($\kappa$-$\varepsilon$), is used to predict the temperature profiles in capsule and the velocity vectors in hot water pipe. The multi-block grids and fine grids embedding are used to join the circle in hot water pipe and square in capsule block. The phase change process of the capsule is quite complex not only because the size of phase change material is very small, but also because phase change material is mixed with the cement to form thermal storage block. In calculation, it's assumed that the phenomena of phase change is limited only the thermal properties of phase change material and the change of boundary is not happened in capsule. The purpose of this study is to calculate the temperature profiles in capsule block and velocity vectors in hot water pipe using the numerical calculation. Two kinds of thermal boundary condition were considered, the first (case 1) is the adiabatic condition for the both outside surfaces of the wall, the second (case 2) is the case in which one surface is natural convection with atmosphere and another surface is adaibatic. Calculation results are shown that the temperature profile in capsule block for case 1 is higher than that for case 2 due to less heat loss in adaibatic surface. Specially, in the domain of near Y=0, the difference of temperature is greater in case 1 than in case 2. The detailed experimental data of capsule block on the temperature profile and the thermal properties such as specific heat and coefficient of heat transfer with the various temperature are required to predict more exact phenomena of heat transfer.

• Journal of Energy Engineering
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• v.2 no.3
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• pp.258-267
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• 1993

A mathematical model has been developed to describe heat transfer phenomena in a PCM (phase change material) module for development of an energy recovery system. The PCM module, melting point of which is around 1673 K, consists of silicon(96.8%), aluminium(2.7%) and marginal amounts of impurities such as Ca, Fe and Ti. The module is covered by a capsule that consists of SiC(58%) and graphite(42%). Physical properties that are required for model predictions were cited from the references. The apparent capacity method and the postiterative method wert used in the mathematical model to describe the phase changing mechanism. Temperature and velocity of fluid are the major variables in the model calculation. For the gas temperature of 1773 K that simulates real operating conditions, the prediction shows that PCM is rapidly melted to axial direction. However, for the gas temperature of 3000 K that is higher than the real conditions, PCM is melted rapidly to the radial direction. The gas velocity has no influence on the melting phenomena of the PCM except when the gas velocity is relatively low. At the low gas velocity asymmetry of the temperature profiles in PCM is obtained.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.10 no.1
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• pp.12-21
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• 1981

The Enthalpy Model was verified in order to analyze two- dimensional phase change problems. By using the Enthalpy Model, interface locations, frozen fraction rates, heat flux distribution rut cooled surfaces, and surface-integrated heat flux were purely numerically calculated in rectangular thermal storage units, whose initial condition was saturated liquid and phase change material was cooled on its boundaries by convective heat transfer. The calculations were performed for various Stefan numbers and Biot numbers. The effect on those dimensionless numbers were explained.

• Solar Energy
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• v.17 no.2
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• pp.67-74
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• 1997

Spherical shape of phase change material(PCM) has been prepared by using sodium acetate trihydrate as a latent heat storage medium. Gelatin was used as an effective thickener to prevent undesirable phase separation. Sodium pyrophosphate decahydrate was used as nucleator to decrease the degree of supercooling in the thickened phase change material. Spherical PCM particles of 3-3.5 mm in diameter continuously manufactured with molten PCM with those conditions. The particle size of PCM was not affected by the effluent velocity of molten PCM in range of 1.3-1.8 ml/min. DSC, SEM and XRD were also used to characterize the properties of PCM particles.

• Solar Energy
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• v.19 no.2
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• pp.57-65
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• 1999

In this study $H_2O$-NaCl mixture was selected as a cold thermal storage material and its phase change temperature($liquid{\Leftrightarrow}solid$) was controlled with the molar concentration of NaCl. Ion dipole interaction mechanism and the fusion and crystallization structure of $H_2O$-NaCl were visualized with the low and high concentration of NaCl in the heating and cooling processes. In this study, the original cause of the appearance of two steps phase change period in heating and cooing processes were found by the visualization of the ion dipole interaction mechanism of $H_2O$-NaCl, and the theoretical equation of the phase change temperature variation in the NaCl high molar concentration was rearranged.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.06a
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• pp.207-207
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• 2011

본 논문은 공장 등에서 버려지는 중온온도영역($100{\sim}250^{\circ}C$)에서의 패열을 잠열축열 시스템에서 유용하게 사용을 목적으로 잠열축열재인 에리스리톨와 만니톨 그리고 이것들을 혼합한 혼합물에 대한 조사에 관한 것이다. 또한, 만니톨에 에리스리톨을 첨가하는 것에 의해 융해 응고온도가 조정의 가능성에 대해서도 조사한다. 이때 에리스리톨과 만니톨 그리고 이것들의 혼합물의 융점과 잠열량은 시차주사열량계(DSC)를 이용하여 측정되며, 시험관안에 상변화물질을 충전하여 융해 응고거동을 디지털 카메라를 이용하여 관찰 된다. DSC측정결과에서는 만니톨의 함유량이 50~60mass%에서는 3개의 융점, 70~90mass%에서는 2개의 융점을 나타내는 것을 확인할 수 있었다. 또한 시험관을 이용한 실험결과에서는 만니톨의 함유량에 따라서 각 각 다른 융해 응고거동이 일어나는 것을 확인할 수 있었다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.7
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• pp.301-307
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• 2014

This paper presents a numerical study on the constrained melting of a phase change material inside various capsule containers, using water and HDPE (High Density Polyethylene) as a PCM and a capsule material, respectively. The computations are based on an iterative, finite-volume numerical procedure that incorporates a single-domain enthalpy formulation for simulation of the phase change phenomenon. Using the enthalpy method, various capsule configurations, such as a capsule from E company, an isochoric cylinder capsule, an equivalent diameter sphere capsule, and an isochoric sphere capsule, are used to investigate the effect of capsule configurations on the charging and discharging performance. A transient three-dimensional model is used for each case. The simulation results show that the capsule from E company results in a higher melting and solidification rate of the PCM, than the other capsule configurations considered in this research.