• Journal of the Korean Society of Clothing and Textiles
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• v.20 no.6
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• pp.1071-1083
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• 1996

This study was carried out to obtain some fundamental data for designing thermally comfortable Korean folk clothes (KFC) which were classified into 4 groups according to seasons and materials. It was conducted to find the relationship among structural, thermal, and moisture transfer properties, and then the properties of heat and mositure transfer while changing thickness of air layer of selected similar fabrics with various thickness were examined. The summarized results of this study were as follows ; 1. The relationship between the structrual and thermal properties showed high positive correlation with thickness SE thermal insulation value (TIV), porosity & TIV. 2. The relationship between the structural and mositure transfer properties showed high negative correlation with thickness & moisture vapor permeability (Mp), porosity & Mp respectively. 3. The relationship between the heat and moisture transfer properites showed high negative correlation with qmax, air permeability (Ap), Mp & TIV while showed high positive with Ap & Mp respectively. 4. Resistance to dry heat transfer according to thickness of air layer for KFC was increassed rapidly up to 2 mm and above this increasing rate was reduced. Resistance to evaporative heat transfer was remarkable changes in 6∼8 mm but slowly in 6∼8 man. 5. Mioisture permeability index (i) according to thickness of air layer for KFC showed the greatest value at 2 mm but had not difference between groups according to thickness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.363-372
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• 2000

An experiment was carried out to evaluate the heat transfer enhancement and the pressure drop characteristics for liquid nitrogen using wire-coil-insert technique under horizontal two-phase conditions. The tube inner diameters were 8 mm and 15 mm, respectively and the tube length was 4.7 m. The helix angle of the wire coil insert was $50^{\circ}$ and its length was 4.7 m. Heat transfer coefficients for both the plain and the enhanced test tubes were calculated from the measurements of temperatures, flow rates and pressure drops. A correlation in a power-law relationship of the Nusselt number, Reynolds number and Prandtl number for the heat transfer was proposed which can be available for design of cryogenic heat exchangers. The correlation showed that heat transfer coefficients for the wire-coil inserts were much higher than those for plain tubes, increased by more than $1.8{\sim}2.0$ times depending upon the range of the equivalent Reynolds number. The correlation was compared with other various correlations in the turbulent flow conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.730-740
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• 1996

Boiling heat transfer coefficients of pure refrigerants (R22, R32, R134a, R125, R290, and R600a) and refrigerant mixtures (R32/Rl34a, R290/ R600a, and R32/R125) are measured experimentally and compared with Chen's correlation. The test section is a seamless stainless steel tube with inner diameter of 7.7mm and uniformly heated by applying electric current directly to the tube. Heat fluxes range from 10 to 30kW$^2$. Mass fluxes are set to 424 ~ 742kg/m$^{2}$s for R22, R32, R134a, R32/R134a, and R32/Rl25 ; 265 ~ 583kg/m$^{2}$s for R290, R600a, and R290/R600a. Heat transfer coefficients depend strongly on heat flux at a low quality region and become independent as quality increases. Convective boiling term in the Chen's correlation predicts experimental data of the pure refrigerants fairly well (relative error of 12.1% for the data of quality over 0.2). The correlation for pure substances overpredicts the heat transfer coefficients for nonazeotropic refrigerant mixtures.

• Nuclear Engineering and Technology
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• v.28 no.6
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• pp.532-541
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• 1996

Theoretical and numerical study on heat transfer and evaporation in the vertical channel has been carried out and basic correlations have been derived for the heat transfer evaluation of PCCS. Analysis program was developed with low-Reynolds-number k-$\varepsilon$ model and surface transfer rates were calculated for the turbulent natural convection in the vertical channel. In relation to dry cooling by buoyancy-driven air, first, the system parameters which govern overall heat transfer rate are determined through the adequate nondimensionalization procedure. After comparison with existing experimental data, numerical results are used to derive heat transfer correlation by sensitivity calculations. In relation to wet cooling by falling water film, numerical analysis are carried out for evaporation process with real film surface conditions and evaporation correlation is derived through analogy concept and correction factors.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.9
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• pp.768-778
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• 2003

Numerical analysis has been carried out to investigate laminar convective heat transfer in a tube for supercritical water near the thermodynamic critical point. Fluid flow and heat transfer are strongly coupled due to large variations of thermodynamic and transport properties such as density, specific heat, viscosity, and thermal conductivity near the critical point. Heat transfer characteristics in the developing region of the tube show transition behavior between liquid-like and gas-like phases with a peak in heat transfer coefficient distribution near the pseudocritical point. The peak of the heat transfer coefficient depends on pressure and wall heat flux rather than inlet temperature and Reynolds number, Results of the modeling provide convective heat transfer characteristics including velocity vectors, temperature, and the properties as well as the heat transfer coefficient. The effect of proximity to the critical point is considered and a heat transfer correlation is suggested for the peak of Nusselt number in the tube.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.4
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• pp.206-216
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• 2005

Numerical analysis has been carried out to investigate laminar convective heat transfer at zero gravity in a tube for supercritical water near the thermodynamic critical point. Fluid flow and heat transfer are strongly coupled due to large variation of thermodynamic and transport properties such as density, specific heat, viscosity, and thermal conductivity near the critical point. Heat transfer characteristics in the developing region of the tube show transition behavior between liquid-like and gas-like phases with a peak in heat transfer coefficient distribution near the pseudo critical point. The peak of the heat transfer coefficient depends on pressure and wall heat flux rather than inlet temperature and Reynolds number. Results of the modeling provide convective heat transfer characteristics including velocity vectors, temperature, and the properties as well as the heat transfer coefficient. The effect of proximity on the critical point is considered and a heat transfer correlation is suggested for the peak of Nusselt number in the tube.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.15 no.2
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• pp.182-187
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• 1986

Experimental measurements of the heat transfer and heat flux to a jet impinging on a heated surface were obtained in the nucleate boiling regimes. Tes-variables were jet at velocity and aspect ratio ($b/\ell$) of the heated surface. A slope of nucleate boiling curve increased with increasing the aspect ratio of the heated surface, namely approaching a rectangular square, and it is shown that surface tension has an important role for the onset of nucleate boiling heat transfer. A generalized correlation of the jet nucleate boiling heat transfer. A generalized correlation of the jet nucleate boiling heat transfer was found using a pi theorem.

• Journal of Energy Engineering
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• v.23 no.3
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• pp.191-197
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• 2014

To increase the heat transfer rate of the air pre-heating heat exchanger used for the condensing boiler, We investigated condensation heat transfer coefficients through plasma surface treatment. The hydrophilic surface showed about 10% increase in heat transfer rate than original plate. It shows that Shah correlation can be used to predict the condensation heat transfer coefficient on the original surface within 10% error range after the compatison between Shah correlation and the condensation heat transfer coefficients measured on the hydrophilic surface and original surface. Therefore, we have shown that Shah correlation is available when designing the air pre-heating heat exchanger using the original surface in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1069-1078
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• 2013

Recently, condensation heat exchangers have been studied for applications to the passive cooling systems of nuclear plants. To design vertical-type condensation heat exchangers in secondary passive cooling systems, TSCON (Thermal Sizing of CONdenser), a thermal sizing program for a condensation heat exchanger, was developed at KAERI (Korea Atomic Energy Research Institute). In this study, the existing condensation heat transfer correlation of TSCON was evaluated using 1,157 collected experimental data points from the heat exchanger of a secondary passive cooling system for the case of pure steam condensation. The investigation showed that the Shah correlation, published in 2009, provided the most satisfactory results for the heat transfer coefficient with a mean absolute error of 34.8%. It is suggested that the Shah correlation is appropriate for designing a condensation heat exchanger in TSCON.

• Solar Energy
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• v.19 no.2
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• pp.29-36
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• 1999

Heat transfer characteristics of a low temperature latent heat storage system during the heat storage stage was examined for the circular finned tubes using fatty acid which shows the big density difference during melting as phase change materials. The heat storage vessel has the dimension of 530 mm height, 74 mm inside diameter and inner heat transfer tube is 480 mm in height and 13.5 mm outside diameter. Hot water was employed as the heat transfer fluid. During the heat storage stage, it was found that both conduction and natural convection were the major heat transfer mechanism. It was also found that the effect of natural convection on the heat transfer was more significant for the unfinned tube system than that for the finned tube system. The experimentally determined overall heat transfer coefficients were in the range of $50{\sim}250W/m^2K$ and the correlation for natural convection heat transfer as a function of Nusselt and Rayleigh number was proposed.