• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.11
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• pp.3706-3713
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• 1996

A numerical study on natural convection induced by free surface heat flux and cold left and hot right walls in glass melting furnaces has been performed. A function of heat flux derived from the combustion environments of actual glass melting furnace is applied to thermal boundary condition at free surface. Fundamentally there exist two flow cells in cavity (left counterclockwise one and right clockwise one). The effects of heat flux and Rayleigh number are investigated through two-dimensional steady-state assumption. The convection strength of two flow cell located in left region continuously increases. In the mean time the strength of flow cell in right region increases and then decreases. Critical Rayleigh number in which two flow cells take place above and below show linear dependence on the free surface heat flux. To maintain the traditional flow pattern (left and right flow cells) in glass melting furnace, Rayleigh number is recommended to be below 10$^{5}$ .

• The Journal of Natural Sciences
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• v.10 no.1
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• pp.1-7
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• 1998

A Lennard-Jones fluid layer adsorbed on a smooth solid surface was studied at coverages $\theta$ ~ 0.8 to 1.8 on an isotherm by performing intensive grand canonical Monte Carlo simulations. The results clearly show a picture of two-step melting process which used to be observed in recent thermodynamic measurements of argon monolayer melting on graphite. The observed melting process consist of an abrupt density change followed by a gradual transition. Snapshots of monolayer configurations indicate that the creation and dissociation of a dislocation pair are involved in the melting mechanism. Taking the effect of system size into account, it is suggested that, while the abrupt density change may be not related to the theory of Kosterlitz, Thouless, Halperin, Nelson, and Young (KTHNY), the second gradual transition is probably a KTHNY-type melting transition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.4
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• pp.547-555
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• 1995

Melting process of ice in a rectangular cavity with different temperature walls has been studied experimentally. Front shape of ice and melting rate were affected by initial temperature of ice and variation of temperature distribution and density gradient. When the hot wall temperature was below $8^{\circ}C$, the melting rates were higher at the bottom than those of at the top due to the density inversion, but with increasing the hot wall temperature the melting rates at the top were affected by hot wall and were higher than those of at the bottom. When the initial temperature of ice was low, melting rates were low, but with increasing the time melting rates were almost the same with those of each initial temperature of ice.

• Journal of the Korean Society of Visualization
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• v.22 no.1
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• pp.6-17
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• 2024

This study examined the natural convection heat flow characteristics of the melting process of PCM (palm oil) inside a liquid flexitank(bag) for a cargo container. A film heating element was installed on the bottom of the container, and numerical analysis was performed under heat flux conditions of 1,000 to 4,000 W/m². As a result, the melt interface of the PCM rises to a nearly horizontal state over time. In the initial stage, conduction heat transfer dominates, but gradually waves at the cell flow and melt interfaces are formed due to natural convection heat transfer. As melting progresses, the Ra number increases parabolically, and the Nu number increases linearly and has a constant value. The Nu number rises slowly under low heat flux conditions, whereas under high heat flux conditions, the Nu number rises rapidly. As the heat flux increases, the internal temperature oscillation of the liquid phase after melting increases. However, under high heat flux conditions, excess heat exceeding the latent heat is generated, and the temperature of the molten liquid is raised, so the increase in melting rate decreases. Therefore, the appropriate heating element specification applied to a 20-ton palm oil container is 2,000 W/m².

• Solar Energy
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• v.9 no.3
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• pp.44-54
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• 1989

Heat transfer phenomena during inward melting process of the phase change material were studied experimentally. N-docosane paraffin [$C_{22}H_{46}$] is used for phase change material and its melting temperature is $42.5^{\circ}C$. Experiments were performed for melting of an initially no-sub cooled or subcooled solid in a horizontal cylinder, in order to compare and investigate the radial temperature distribution, ratio of melting and melted mass, various energy components stored from the cylinder wall, figure of the melting front in the horizontal cylinder. The solid-liquid interface motion during phase change was recorded photographically. The experimental results reaffirmed the dominant role played by the conduction at early stage, by the natural convection at longer time during inward melting in the horizontal cylinder. Ratio of melting and melted mass are more influenced by wall temperature, rather than by the initial temperature of solid. The latent energy is the largest contributor to the total stored energy.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.12
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• pp.1266-1274
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• 2001

Heat transfer phenomena during melting process of the phase change material (ice) was studied by numerical analysis and experiments. In a horizontal ice storage tube, the natural convection caused an increase in melting rate. However, the reduction of the heating surface area caused a decrease in melting rate. Therefore, during the melting process of ice in a horizontal cylinder, the reduction of the heating surface area should be considered. Under the same heating wall and initial water temperature condition, the melting rate became higher for $V_s/V_tot/=0.545 \;than \;that\; for\; V_s/V_tot$/=1.00 due to the difference in the reduction of heating surface area. A modified melting model considering the equivalent thermal conductivity of liquid phase and volume reduction was proposed. The results of the model were compared with the measured values and found to be in good agreement.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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• pp.13-19
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• 2014

Urea-SCR system is the selective catalytic reduction to reduce nitrogen oxides ($NO_x$) emitted from diesel vehicles. The objective of this study is numerical analysis of 3-dimensional unsteady melting problems of frozen urea by using an electric heater. It can be applied to determine capacity of power with respect to time and the location of the urea suction pipe in urea storage tank. The study includes the change of liquid volume fraction, temperature profiles and a influence of natural convection by using the commercial software STAR-CCM+(v7.06). The accuracy of the numerical analysis is estimated by comparisons with experimental data. After validation, a numerical analysis for freezing urea is conducted with four different heating power. From the results, it was found that relation of velocity of phase interface and amount of melting urea by increasing heating power in a container. There is also a difference in trend between velocity of phase interface and amounts of melting urea because of effect of natural convection.

• Journal of the Korean Society of Visualization
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• v.1 no.2
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• pp.52-57
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• 2003

The present paper investigated the effect of ultrasonic vibrations on the melting process of a phase-change material (PCM). The melting process in the square cavity with a heated vertical wall has been studied in terms of acoustic streaming. In the present study, applying with ultrasonic vibrations to the liquid were found to induce acoustic streaming which was clearly observed using by a particle image velocimetry (PIV) and a thermal infrared camera. The experimental results revealed that acoustic streaming could accelerate the melting process as much as 2.5 times, compared to the rate of natural melting (i. e., the melting without acoustic streaming). In addition, temperature and Nusselt numbers over time provided conclusive evidence of the important role of the acoustic streaming on the melting phenomena of the PCM.

• Solar Energy
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• v.12 no.3
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• pp.60-69
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• 1992

Heat transfer characteristics and heat storage rate for vertical cylinder packed with paraffin as a latent heat storage material were theoretically studied. Conduction and convection mechanism were applied to the solid and liquid phase, respectively, and the results were compared with that of pure conduction model. The effects of heating temperature, initial solid temperature and aspect ratio on rate of storage were also studied. In the initial stage of melting, the natural convection is nearly restricted by the friction at the wall and the phase boundary. But it is generated when about 40% of solid melts and again it shrinks by the hot liquid situated on the upper part of the cylinder. So overall melting rate is higher then that for pure conduction model. The increase in heating temperature and aspect ratio activates the natural convection, so melting rate becomes higher. And the larger the aspect ratio, the greater the difference between upper and lower size of the solid. In the initial stage of melting, the initial temperature of solid paraffin has great effect on the melting rate, but as melting proceeds its effect lessens gradually.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.1
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• pp.23-29
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• 2002

Solid-liquid phase change (i.e. melting or solidification) occurs in a number of situations of practical interest. Some common examples include the melting of edible oil, metallurgical process such as casting and welding, and materials science applications such as crystal growth. Therefore, due to the practical importance of the subject, there have been a large number of experimental and numerical studies of problems involving phase change during the past few decades. Also, this study presented the effective way to enhance phase change heat transfer.