• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.12
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• pp.52-58
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• 2019

This study numerically analyzed the icing process in a U-shaped pipe exposed to the outside by considering the mushy zone of freezing water. Numerical results showed that the flow was pulled outward due to the U-shaped bend in the freezing section exposed to the outside, which resulted in the ice wave formation on the wall of the bended pipe behind. At the same time, the formation of a corrugated ice layer became apparent due to the venturi effect caused by the ice. The factors affecting the freezing were investigated, including the change of the pipe wall temperature, the water inflow velocity, and the pipe bend spacing. It was found that, as a whole, the thickness of the freezing layer increased as the pipe wall temperature decreased. It was also found that the freezing layer became relatively thin when the inflow rate of water was increased, and that the spacing of the pipe bends did not significantly impact the change in the freezing layer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.3
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• pp.175-182
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• 1992

Freezing of the binary solution ($H_2O-NaCl$) saturating a packed bed of spheres is investigated experimentally. The system is cooled through its top surface, and the bottom is maintained at a temperature above the liquidus. Experiments are performed on the hypolutectic side, and the cold wall temperature is lower than the eutectic point. The effects of initial mixture concentration, superheat and glass bead diameter on temperature and concentration distributions are investigated. Supercooling was observed only at early times of the freezing process for experiments with 5% initial salt concentration. Flow visualization experiments and mushy-liquid interface position observations revealed natural convection in the liquid region. Remelting phenomena was not observed at both the solid-mushy and mushy-liquid interfaces.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.1
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• pp.114-120
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• 2020

In this study, the process of freezing around two consecutively arranged channel tubes used for evaporator heat exchange was numerically investigated. Numerical results confirmed that the vortex occurred between the front channel and the rear channel and also that the vortex occurred due to the rapid change of the channel at the rear of the rear channel. These vortices were found to play a role in reducing the ice layer to some extent by the growth of the ice layer at the front and rear of the channel tube. The freezing layer showed a tendency to gradually increase as it passed through the channel pipe. As the wall temperature in the channel pipe decreased, the thickness of the freezing layer increased. As the flow rate of water slowed, the thickness of the freezing layer became thicker. In particular, in the case of a slow flow rate of 0.03 m/s, the freezing layers of the front channel pipe and the rear channel pipe were connected to each other. The narrower the channel, the thinner the freezing layer was in both the front and rear channel tubes. It is found that these thin freezing layers are caused by the low thickness of the temperature boundary layer formed around the channel tube.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.8 no.3
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• pp.19-28
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• 2012

In a heat only boiler system of a steam power plant, outdoor air required for combustion is made to pass through indoor space for increasing the boiler efficiency. Due to heat generated by various equipments, temperature of the air that enters the boiler will increase resulting in combustion efficiency. If the outdoor air temperature is low, however, this will cause freezing and bursting of pipes which are filled with water. It is especially fatal to small diameter pipes and pipes connected to measuring instruments. The purpose of this study is find operation and outdoor conditions where this phenomena can happen and also establish preventive measures to avoid this problem.

• International Journal of Highway Engineering
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• v.18 no.2
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• pp.83-90
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• 2016

PURPOSES : Nowadays, cavity phenomena occur increasingly in pavement layers of downtown areas. This leads to an increment in the number of potholes, sinkholes, and other failure on the road. A loss of earth and sand from the pavement plays a key role in the occurrence of cavities, and, hence, a structural-performance evaluation of the pavement is essential. METHODS: The structural performance was evaluated via finite-element analysis using KPRP and KICTPAVE. KPRP was developed in order to formulate a Korean pavement design guide, which is based on a mechanical-empirical pavement design guide (M-EPDG). RESULTS: Installation of the anti-freezing layer yielded a fatigue crack, permanent deformation, and international roughness index (IRI) of 13%, 0.7 cm, and 3.0 m/km, respectively, as determined from the performance analysis conducted via KPRP. These values satisfy the design standards (fatigue crack: 20%, permanent deformation: 1.3 cm, IRI: 3.5 m/km). The results of FEM, using KICTPAVE, are shown in Figures 8~12 and Tables 3~5. CONCLUSIONS: The results of the performance analysis (conducted via KPRP) satisfy the design standards, even if the thickness of the anti-freezing layer is not considered. The corresponding values (i.e., 13%, 0.7 cm, and 3.0 m/km) are obtained for all conditions under which this layer is applied. Furthermore, the stress and strain on the interlayer between the sub-grade and the anti-freezing layer decrease gradually with increasing thickness of the anti-freezing layer. In contrast, the strain on the interlayer between the sub-base and the anti-freezing layer increases gradually with this increase in thickness.

• Solar Energy
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• v.13 no.2_3
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• pp.53-64
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• 1993

This study investigated heat transfer phenomena during the freezing of an initially superheated or non-superheated liquid in a cooled cylinder tube. Numerical and experimental method were performed to obtatin the temperature and velocity distribution, the shape of interface. Natural convection effects in the superheated liquid were confined and moderated a short freezing time. After natural convection ceases, heat conduction dominated in the whole paraffin, so Crystal and much-zone were found out in PCM. Initial superheating of liquid tended to morderatly diminish the frozen layer thickness at short freezing times but little effect on the these quantities at longer times. On the amount of frozen mass, Iintial liquid superheating is less affected than tube wall subcooling.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.10
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• pp.3313-3321
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• 1996

A fundamental study in cooling and solidification process focused on ice storage was performed, including the interesting phenomena of density inversion, supercooling and dendritic ice. A numerical study was performed for natural convection and ice formation in the cooling and freezing processes with supercooling in a space between double cylinders. When water was cooled under the freezing point by a cooling wall in a cavity, solidification was not started at once, but a subcooled region was formed near the wall. Especially, when the cooling rate was low, subcooled region extended to a wide area. However, after a few minutes, supercooling is released by some triggers. Dendritic ice is suddenly formed within a subcooled region, and a dense ice layer begins to be developed from the cooling wall. Due to the difficulties, most previous studies on solidification process with numerical methods had not treated the supercooling phenomena, i.e. the case considering only the growth of dense ice. In this study, natural convection and ice formation considering existence of supercooling and dendritic ice were analyzed numerically with using finite difference method and boundary fixing method. The results of numerical analysis were well compared with the experimental results.

• Korean Journal of Crystallography
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• v.13 no.3_4
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• pp.172-176
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• 2002

Pyroelectric properties and relaxation phenomena in Pb(Mg /sub 1/3/Nb/sub 2/3/)O₃-PbTiO₃ solid solution system were studied to establish the phase relation of the solid solution system. The dielectric constants and the pyroelectric coefficients of (1-x)PMN-xPT (x = 0.1∼0.4) system were investigated in the phase transition temperature range of -40°C∼200°C. The freezing temperature was calculated by fitting the experimental data with the Vogel-Fulcher relation. With all the experimental data, a modified phase diagram of the (1-x)PMN-xPT system was suggested.

• Journal of the Korean Geotechnical Society
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• v.28 no.5
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• pp.85-94
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• 2012

Recently, growing interests in frozen ground have stimulated us to advance fundamental theories and systematic researches on soil behavior under freezing conditions. Unlike the well-established soil mechanics theory, temperature variation and phase change of pore-water cause water migration to cold side, ground heaving, sharp increase in earth pressure, etc., which bring about serious problems in frozen geotechnical structures. Elasto-plastic mechanical constitutive model for frozen/unfrozen soil subjected to fully coupled THM phenomena is formulated based on a new stress variable that is continuous in frozen-unfrozen transitional regions. Numerical simulations are conducted to discuss numerical reliability and applicability of the developed constitutive model: one-dimensional heaving pressure, tri-axial compression test, and one-side freezing tests. The numerical results show that developed model can efficiently describe complex THM phenomena of frozen soil, and they can be utilized to analyze and design the geotechnical structures under freezing conditions, and predict their long-term behavior.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.277-280
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• 2008

Reinforced concrete structures have an excellent durability under a good construction and continuous maintenance. But reinforced concrete construction is influenced by atmospheric phenomena and it is creating a deterioration. One of the deterioration cause on concrete is a freezing and thawing action. Freezing and thawing leads to the reduction in concrete durability by the cracking or surface spalling. If we are carried out freezing and thawing, deterioration of reinforced concrete construction will be reduction. Therefore, this study was performed to investigate the flexural behavior of reinforced concrete beams exposed to freezing and thawing cycles. Thee presence of damage and cycles were considered as variablees in this study.