• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.274-280
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• 2005

The objective of this study Is to investigate the heat transfer performance of plate discrete fin-and-tube heat exchangers with large fin pitch. In this study, twenty-two heat exchangers were tested with a variation of fin pitch, number of tube row, longitudinal tube pitch and fin alignment. Discrete fin type exchangers improved heat transfer performance more than 10% compared to tile continuous fin type heat exchangers. The air-side heat transfer coefficient decreased with a reduction of the fin pitch and an increase of the number of tube row, The staggered fin alignment improved heat transfer performance more than 6% compared to the inline fin alignment. The effect of longitudinal tube pitch was insignificant on the j-factor and experiments found opposite effects on the j-factor with respect to fin alignment. Heat transfer correlations were developed from the measured data for flat plate discrete fin-and-tube heat exchangers with large fin pitch. The correlations yielded good predictions of the measured data with mean deviations of 1,4% and 0.3% for tire inline and staggered tube alignment, respectively.

• Journal of Mechanical Science and Technology
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• v.16 no.3
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• pp.354-362
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• 2002

In this paper, the heat transfer characteristics of a self-oscillating heat pipe are experimentally investigated for the effect of various working fluid fill charge ratios and heat loads. The characteristics of temperature oscillations of the working fluid are also analysed based on chaotic dynamics. The heat pipe is composed of a heating section, a cooling section and an adiabatic section, and has a 0.002m internal diameter, a 0.34m length in each turn and consists of 19 turns. The heating and the cooling portion of each turn has a length of 70mm. A series of experiments was carried out to measure the temperature distributions and the pressure variations of the heat pipe. Furthermore, heat transfer performance, effective thermal conductivity, boiling heat transfer and condensation heat transfer coefficients are calculated for various operating conditions. Experimental results show the efficacy of this type of heat pipe.

• Journal of ILASS-Korea
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• v.24 no.4
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• pp.203-208
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• 2019

In general, the oxi-nitriding method is well known as such a surface treatment way for substantial enhancement in corrosion resistance, even comparable to that of titanium. However, there are still lacks of information on thermal performance of the oxi-nitriding surface being of additional compound layers on the base substrate. Above all, the quantitative measurement of its thermal performance still was not evaluated yet. Thus, the present study experimentally measures the thermal resistance of the oxi-nitriding surface during droplet evaporation and then estimates heat transfer performance with the use of the onedimensional heat transfer model in vertical direction. From the experimental results, it is found that the total evaporation time slightly increased with the thermal resistance caused by the oxi-nitriding layer, showing a maximum difference of approximately 20% with that of the bare surface. Although the heat transfer performance of oxi-nitriding surface became slightly lower than that of the bare surface, the oxi-nitriding surface exhibits much better heat transfer performance compared to titanium.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1533-1542
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• 2003

In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased, the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio of 40. vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90$^{\circ}$ the pressure wave was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency of pressure oscillation was the highest.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.7
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• pp.642-648
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• 2000

Falling film heat transfer analyses with aqueous lithium bromide solution were peformed to investigate the transfer characteristics of the copper tubes. Finned(knurled) tube and a smooth tube were selected as test specimens. Averaged generation fluxes of water and the heat transfer performances(heat flux, heat transfer coefficient) were obtained. The results of this work were compared with the data reported previously. As the film flow rate of the solution increased, the generation fluxes of water decreased for both tubes. The reason is estimated by the fact that the heat transfer resistance with the film thickness increased as the film flow rate increased. The effect of the enlarged surface area at the knurled tube was supposed to be dominant at a small flow rate. The generation fluxes of water increased with the increasing degree of tube wall superheat. Nucleate boiling is supposed to occur at a wall superheat of 20 K for a smooth tube, and at 10 K for a knurled tube. The heat transfer performance of the falling film was superior to pool boiling at a low wall superheat below 10 K for both tubes tested. The knurled tube geometry showed good performance than the smooth tube, and the increased performance was mainly came from the effect of the increased heating surface area.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.2
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• pp.73-79
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• 2001

Experiment were carried out to investigate the heat transfer characteristics of an aluminum foam block as a porous heat sink on a heat source by a vertical air jet impingement that can be applied for electronics cooling. The performance of the aluminum foam heat sink was evaluated by the convective heat transfer coefficient on the heat source. At a fixed porosity, pore density ($\beta$) of the foam and Reynolds number Re were varied in the range of $\beta$a=10, 20, 40 PPI(Pore Per Inch) and $850\leqRe\leq25000$. A nozzle diameter and the nozzle-to-plate spacing were also varied. It was found that the convective heat transfer was enhanced by the aluminum foam heat sink with lower pore density due to relatively intensified flow through the foam block. The aluminum foam block with much reduced weight shows slightly better performance with larger Nusselt number, compared with the convectional heat sink.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.468-476
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• 2002

This paper deals with heat and mass transfer characteristics and performance evaluation of a counter flow double-tube condenser for a multi-component refrigerant mixture. The local heat and mass transfer characteristics of ternary zeotropic refrigerant mixtures composed of HFC32/HFC125/HFC134a are evaluated for a counter flow double-tube condenser cooled by water. Then, the local values of vapor quality, thermodynamic states at bulk vapor, vapor-liquid interface and bulk liquid, heat flux and condensation mass flux are obtained. The heat exchange performance for ternary zeotropic refrigerant mixtures composed of HFC32/HFC125/HFC134a on the total pressure drop and the heat transfer characteristics are also compared with those for R404A, R410A, R502, R22, R32, Rl23 and R134a.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.2
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• pp.57-62
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• 2017

The heat transfer performance of a multi-heat-source fluidized bed heat exchanger was analyzed. The fluidized bed heat exchanger examined in this study can simultaneously recover the waste heat from gas, water vapor, and hot water. The effects of waste water flow rate, gas flow rate, and cooling water flow rate were examined to find their experimental correlations with the heat transfer coefficient. A computer program using the correlations was developed in this study to predict the thermal performance of the fluidized bed heat exchanger. The calculated heat transfer rates of gas, water vapor, waste water, and cooling water were compared with the measured values. It was found that the error of the calculated values was less than 12%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.2
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• pp.117-124
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• 2005

Aluminum plate heat exchanger, rotary wheel heat exchanger, and heat pipe heat exchanger have been used (or ventilation heat recovery in the air-conditioning system. The purpose of this research is to develop high efficiency plastic plate heat exchanger which can substitute aluminum plate heat exchanger. Because thermal conductivity of plastic is quite small compared to that of aluminum, various heat transfer enhancement techniques are applied in the design of plastic plates. Five types of heat exchanger model are designed and manufactured, which are plate type, plate-fin type, turbulent promoter type, corrugate type, and dimple type. Thermal performance and pressure loss of each heat exchangers are measured in various operating conditions, and compared each other. Test results show that heat transfer performance of corrugate type, turbulent promoter type, and dimple type are increases about $43\%$, $14\%$, and $33\%$ at the equivalent fan power compared to those of plate type, respectively. On the other hand, the heat transfer performance of plate-fin type decreases $9\%$ because fins can not play their own role.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.557-563
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• 2001

Small capacity gas absorption systems for cooling and heating have been favorably considered to reduce the seasonal imbalance of electrical loads and LNG consumption recently. A multifunctional plate-fin heat exchanger was adopted as an absorber and the performance was tested and analyzed to reduce the size and weight of the absorption heat pump. The test was performed using breadboard type ammonia absorption machine. The performance was compared with the plate type absorber and there was little difference in heat and mass transfer characteristics. The heat and mass transfer performance was a function of poor solution and vapor flow rates and the mass transfer was dependent on vapor flow rate more than heat transfer.