• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.2
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• pp.119-126
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• 1990

In this study, the overall heat transfer coefficients are calculated on fluidized bed double pipe heat exchanger and single phase double pipe heat exchanger at the same condition. The effect of the particle size, its material, fluidizing velocity and static bed height on overall heat transfer coefficient has been investigated. The main conclusions obtained from the experiment are as follows. 1. The overall heat transfer coefficient of the fluidized bed heat exchanger is higher than that of single phase forced convective heat exchanger (maximum 2.3 times) 2. The value of the overall heat transfer coefficient increase with an increase in static bed height and decrease with an increase in particle size. 3. For the same particle size, the particle of low density can obtain higher overall heat transfer coefficient than that of high density.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.419-424
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• 2008

Heat transfer and pressure drop characteristics of welded plate heat exchanger are studied to apply it for the solution heat exchanger of 210RT absorption system. This study quantifies the effect of mass flow rate and strong solution concentration on the heat transfer coefficient and pressure drop in the plate heat exchanger. The concentration of weak solution is fixed at 55% and the strong solution varies 55%, 57%, and 59% in mass. The results show that the overall heat transfer coefficient and pressure drop increase linearly with increasing Reynolds number. It is also found that the heat transfer coefficient of hot side increases with increasing the concentration of strong solution while the strong solution concentration has no effect on heat transfer coefficient of cold side.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.5
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• pp.754-761
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• 2004

In this paper, evaporating heat transfer characteristics in the refrigeration and air-conditioning facilities were studied using the environmentally friendly refrigerants R-1270 (Propylene). R-290 (Propane). R-600a (Iso-butane) and HCFC refrigerant R-22 The test tube was surrounded by an annulus with water flowing counter to the refrigerant. The tube is copper. with an outside diameter of 12.7mm and the wall thickness of 1.315mm. The test results showed that the local evaporating heat transfer coefficients of hydrocarbon refrigerants were superior to that of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-1270. The average evaporating heat transfer coefficient increased with the increase of the mass velocity and it showed the higher values in hydrocarbon refrigerants than R-22 Comparing the heat transfer coefficient of experimental results with that of other correlations. the presented results had agood agreement with the Kandlikar's correlation. This results form the investigation can be used in the design of heat transfer exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.425-429
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• 2004

In real design of the high & interim pressure turbine casing, it is one of the important things to figure out its thermal strain exactly. In this paper, with the establishment of the new concept for the heat transfer coefficient of steam that is one of the factors in analysis of the thermal stress for turbine casing, an analysis was done for one of the high & interim pressure turbine casings in operating domestically. The sensitivity analysis of the heat transfer coefficient of steam to the thermal strain of the turbine casing was done with a 2-D simple model. The analysis was also done with switching of the material properties of the turbine casing and resulted in that the thermal strain of the turbine casing was not so sensitive to the heat transfer coefficient of steam. On the basis of this, 3-D analysis of the thermal strain for the high and interim pressure turbine casing was done.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.294-302
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• 1997

Falling-film evaporation experiments for aqueous solution of lithium bromide (LiBr) were performed on a horizontal smooth 19.05-mm-dia copper tube. Average heat transfer coefficients were obtained with varied film Reynolds numbers, system pressures, LiBr concentrations and degrees of wall superheat. Heat transfer coefficients increase with increasing system pressure and decreasing concentration. For degrees of wall superheat, the heat transfer coefficient did not't show the distinct trend. For this experimental ranges, heat transfer coefficients showed maximum values at an optimal film Reynolds number. The results of this work were compared with pool boiling data reported previously, and it was shown that the heat transfer performance is superior to the pool boiling.

• Journal of Mechanical Science and Technology
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• v.14 no.5
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• pp.537-546
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• 2000

The heat transfer characteristics of refrigerant-oil mixture for horizontal in-tube evaporator have been investigated experimentally. A smooth copper tube and a micro-fin tube with nominal 9.5 mm outer diameter and 1500 mm length were tested. For the pure refrigerant flow, the dependence of the axial heat transfer coefficient on quality was weak in the smooth tube, but in the micro-fin tube, the coefficients were 3 to 10 times greater as quality increases. Oil addition to pure refrigerant in the smooth tube altered the flow pattern dramatically at low mass fluxes, with a resultant enhancement of the wetting area by vigorous foaming. The heat transfer coefficients of the mixture for low and medium qualities were increased at low mass fluxes. In the micro-fin tube, however, the addition of oil deteriorates the local heat transfer performance for most of the quality range, except for low quality. The micro-fin tube consequently loses its advantage of high heat transfer performance for an oil fraction of 5%. Results are presented as plots of local heat transfer coefficient versus quality.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.15-16
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• 2014

With the increasing trend in CFB(Circulating Fluidized Bed) boiler scale, the EHE(External Heat Exchanger) must be adopted to the large-scale boilers to recover insufficient heat transfer surface. In this study, the numerical analysis model for EHE in commercial 300MWe CFB boiler was developed with the inclusion of mechanistic model, which enables the heat transfer prediction. Finally, the calculated absorbed heat and derived heat transfer coefficient are evaluated through the verification with experimental data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.2
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• pp.106-112
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• 2008

In this paper, the experimental results on evaporation heat transfer characteristics were reported for a micro-fin tube using $CO_2$. An experimental refrigerant loop had been established to measure the evaporation heat transfer coefficient and pressure drop of $CO_2$. Experiments were conducted for mass fluxes, heat fluxes, saturation temperatures and PAG oil concentrations. With increasing the heat flux and the saturation temperature, the evaporation heat transfer coefficient increased. At the higher mass flux, however, the exit vapor quality of the micro-fin tube was to be lower. The peak of the heat transfer coefficient was shifted toward low quality region. The evaporation pressure drop increased as the mass flux increased and the saturation temperature decreased. As PAG oil concentration increased, the evaporation heat transfer coefficient decreased and the dryout was delayed by oil addition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.11
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• pp.718-725
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• 2011

Characteristics of flow boiling heat transfer in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having 205 ${\mu}m$ of bottom width, 800 ${\mu}m$ of depth, $3.6^{\circ}$ of sidewall angle, and 7 cm of length. Tests were performed with R113 over a mass velocity range of 150~920 $kg/m^2s$, heat flux of 10~100 $kW/m^2$ and inlet pressures of 105~195 kPa. Flow boiling heat transfer coefficient in microchannels was found to be dominated by heat-flux. However the effect of mass velocity was not significant. Contrary to macrochannel trends, the heat transfer coefficient was shown to decrease with increasing thermodynamic equilibrium quality. A new correlation suitable for predicting flow boiling heat transfer coefficient was developed based on the laminar single-phase heat transfer coefficient and the nucleate boiling dominant equation. Comparison with the experimental data showed good agreement.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.3
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• pp.174-183
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• 2001

Experimental study has been carried out on the characteristics of pressure drop and heat transfer of brazed plate heat exchangers using R-404A. Data are presented for the following range of variables: the mass flux ($20~80kg/m^2s$), chevron angle($20^{circ}C,\;35^{circ}C,\;45^{circ}C$) and inlet pressure of he refrigerant (1.4 and 1.6 MPa). for both subcooled and tow-phase flow, as chevron angle increases, pressure drop and heat transfer coefficient decrease. Condensation hat transfer coefficient and pressure drop was compared with the previously proposed correlations. Among them, Traviss correlation agreed with experimental results within -35~82% for heat transfer coefficient and -73~93% for pressure drop.