• Proceedings of the KSME Conference
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• 2000.04b
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• pp.90-95
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• 2000

Condensation heat transfer experiments for R-22 and R-407C refrigerants mixed with mineral oil and POE oil respectively were performed in straight and U-bend sections of a microfin tube. Experimental parameters were an oil concentration from 0 to 5%, a mass flux from 100 to $400 kg/m^2s$ and an inlet quality from 0.5 to 0.9. The enhancement factors for R-22 and R-407C refrigerants at the first straight section decreased continuously as the oil concentration increased. They decreased rapidly as the mass flux decreased and inlet quality increased. The heat transfer coefficients in the U-bend were the maximum at the $90^{\circ}$ position. The heat transfer coefficients at the second straight section within the dimensionless length of 48 were larger by a maximum of 33% than the average heat transfer coefficients at the first straight section.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.93-96
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• 2006

The heat transfer enhancement by pulsatile flow in the plate heat exchanger has been investigated numerically in the present study. The numerical study was performed in the range of the mass flux from 0.04 to 0.12 kg/s. The results showed that the pulsatile flow produces resonating vortex shedding at the groove sharp edges and a strong transient vortex rotation within the grooved channels. As a result, the mixing between the trapped volume in the grooved cavity and the main stream was enhanced. Good agreements between the predictions and measured data are obtained in steady flow. And the heat transfer of pulsatile flow is about 2.4 times than steady flow when frequency is 10 Hz and the mass flux of cold side is 0.04 kg/s.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.346-350
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• 2005

Effects of the changes of a film cooling mass flow rate and operating conditions on the heat flux characteristics of the subscale calorimeter were studied. A film cooling ring with twelve orifices is inserted between the injector head and the calorimeter. The calorimeter is composed of nineteen cooling channels. When a mass flow rate of film cooling is 10.5 % of a main fuel mass flow rate, maximum heat flux at the nozzle throat is decreased by 30% compared to that without film cooling. In the OD3(of-design point) test result, maximum heat flux at the nozzle throat is increased by 31% compared to that of the DP(design point) test when a film cooling flow rate is zero.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3962-3973
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• 2022

Several critical heat flux (CHF) correlations including the look-up table in the MARS code have been assessed for the prediction of CHF in a downward-flow narrow rectangular channel. For the assessment, we built an experiment database that covers pressures between 1.01 and 39.0 bar, gap sizes between 1.09 and 6.53 mm, mass fluxes up to 25,772 kg/m²s, and under one-sided and two-sided heating conditions. The results of the assessment showed that the Kaminaga correlation has the best overall prediction compared to others. However, because the correlation uses global variables, such as inlet and outlet subcooling and total heat transfer area, it is difficult to use in a system code. A new CHF correlation is then proposed by replacing the global variables in the Kaminaga correlation with local ones and adding correction factors to consider the effect of gap size, mass flux, and the number of heating walls. Additional correction factor is added to consider the effect of inlet subcooling. It is shown that the new one is better than the Kaminaga correlation and it is easy to implement to any system code.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.1
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• pp.55-65
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• 2006

The air and water flow distribution are experimentally studied for a round header - flat tube geometry simulating a parallel flow heat exchanger. The number of branch flat tube is thirty. The effects of tube outlet direction, tube protrusion depth as well as mass flux, and quality are investigated. The flow at the header inlet is identified as annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted configuration, most of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, however, most of the water flows through rear part of the header. The protrusion depth, mass flux, or quality does not significantly alter the flow pattern. Possible explanations are provided based on the flow visualization results. Negligible difference on the water flow distribution was observed between the parallel and the reverse flow configuration.

• Journal of Power System Engineering
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• v.12 no.4
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• pp.26-31
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• 2008

The evaporation heat transfer coefficient and pressure drop of R-22 and R-407C in a small diameter copper tube were investigated experimentally. The main components of the refrigerant loop are a receiver, a compressor, a mass flow mete, a condense and a double pipe type evaporate (test section). The test section consists of a smooth copper tube of 4.3 mm inner diameter. The refrigerant mass fluxes were varied from 100 to $300[kg/m^{2}s]$ and the saturation temperature of evaporator were $5[^{\circ}C]$. The evaporation heat transfer coefficients of R-22 and R-407C increase with the Increase in mass flux and vapor quality. The evaporation heat transfer coefficient of R-22 is about $7.3\sim47.1%$ higher than that of R-407C. The evaporation pressure drop of R-22 and R-407C increase with the increase of mass flux. The pressure drop of R-22 is about $8\sim20%$ higher than that of R-407C.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.216-221
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• 2005

The heat transfer coefficient and pressure drop during gas cooling process of carbon dioxide in a helically coiled tube were investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a double pipe type heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. It was made of a copper tube with the inner diameter of 4.85 [mm], the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were 200${\sim}$600 [kg/$m^2$s] and the average pressure varied from 7.5 [MPa] to 10.0 [MPa]. The main results were summarized as follows: The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.228-233
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• 2000

An experimental study has been performed regarding heat and mass transfer in a falling film absorber of domestic small-sized absorption chiller/heater. Components were concentrically arranged in cylindrical form : from the center, with a series of low temperature generator, absorber and evaporator. The arrangement of such helical-typed heat exchangers allows to make the system more compact as compared to conventional one. Experimental measurements were conducted with a helical absorber using $LiBr+LiI+LiNO_3+LiCl$ and LiBr solutions. As a result, the heat and mass flux performance of $LiBr+LiI+LiNO_3+LiCl$ solution shows the tendency of $2{\sim}5%$ increase. Therefore, $LiBr+LiI+LiNO_3+LiCl$ solution can be taken consideration into applying to small-sized absorption chiller/heater because of using without crystal through high concentration as 4wt% comparing with LiBr solution.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.1
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• pp.25-33
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• 2007

The investigation has been made into the prediction of heat exchange performance of a counter flow type double-tube condenser for natural refrigerant mixtures composed of Propane/n-Butane or Propane/i-Butane in a smooth tube and micro-fin tube. Under various heat transfer conditions, mass flux, pressure drop and heat transfer coefficient of the mixed refrigerants were calculated using a prediction method, when the length of condensing tube, total heat transfer rate, mass flux and outlet temperature of coolant were maintained constant. Also, the predicted results were compared with those of HCFC22. The results showed that the mixed refrigerants of Propane/n-Butane or Propane/i-Butane could be substituted for HCFC22, while the pressure drop and overall heat transfer coefficient of the refrigerants were evaluated together.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.12
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• pp.663-670
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• 2009

Two-phase flow boiling heat transfer of R-410A in horizontal small tubes was reported in the present experimental study. The local heat transfer coefficients were obtained over a heat flux range of 5 to 40 kW/$m^2$ a mass flux range of 170 to 600 kg/$m^2s$, a saturation temperature range of 3 to $10^{\circ}C$, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5 and 3.0 mm, and lengths of 330 and 3000 mm, respectively. The test section was heated uniformly by applying a direct electric current to the tubes. The effects on heat transfer of mass flux, heat flux, inner tube diameter, and saturation temperature were presented. The experimental heat transfer coefficients are compared with six existing heat transfer coefficient correlations. A new boiling heat transfer coefficients correlation based on the superposition model for R-410A in small tubes was developed with mean deviation of 10.13%.