• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.189-194
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• 2005

The evaporation heat transfer and pressure drop of $CO_2$ in a small diameter tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section was made of a horizontal stainless steel tube with the inner diameter of 4.57 mm, and length of 4 m. The experiments were conducted at mass flux of 200 to 700 $kg/m^2s$, saturation temperature of $0^{\circ}C$ to $20^{\circ}C$, and heat flux of 10 to 20 $kW/m^2$ . The test results showed the evaporation heat transfer of $CO_2$ has great effect on more nucleate boiling than convective boiling. The evaporation heat transfer coefficients of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. The evaporation pressure drop of C02 are highly dependent on the mass flux. In comparison with test results and existing correlations, correlations failed to predict the evaporation heat transfer coefficient and pressure drop of $CO_2$, therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient and friction pressure drop of $CO_2$ in a horizontal tube.

• Journal of Welding and Joining
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• v.15 no.3
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• pp.36-46
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• 1997

Dynamics of molten drop detachment in the Gas Metal Arc (GMA) welding is investigated using the Volume of Fluid(VOF) method. The electromagnetic effects are included in the formulation of the VOF method which has been widely used to analyze the dynamics of the fluid having a free surface. The molten drop geometry, pressure and velocity profiles within the drop are calculated numerically in the cases of globular and spray transfer modes. It appears that the velocity and current distribution affect metal detachment. It is found that the taper is formed and maintained during the spray transfer by the electromagnetic force. Predicted results show reasonably good agreement with the available experimental data which validates the application of the VOF method to metal transfer analysis.

• Journal of Fisheries and Marine Sciences Education
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• v.14 no.2
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• pp.177-190
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• 2002

An experimental study was carried out to make clear heat transfer characteristics in flow boiling of binary mixtures of refrigerants R134a and R123 in a uniformly heated horizontal tube. Experiments were run at a pressure of 0.6 MPa both for pure fluids and mixtures in the ranges of heat flux $10{\sim}50{kW/m}^2$, vapor quality 0~100% and mass flux 150-600 $kg/m^2s$. Heat transfer coefficients of mixtures were reduced compared to the interpolated values between pure fluids both in the low quality region where the nucleate boiling is dominant and in the high quality region where the convective evaporation is dominant. Total pressure drop during two-phase flow boiling in a horizontal tube consists of the sum of two components, that is, the frictional pressure drop and pressure drop due to acceleration. The frictional pressure drop is the most difficult component to predict, and makes the most important contribution to the total pressure drop. On the other hand, the acceleration pressure drop resulting from the variation of the momentum flux caused by phase change is generally small as compared to the frictional pressure drop. There is no significant difference in measured pressure drop between mixtures and pure fluids. The correlation of Martinelli and Nelson predicted most of the present data both for pure and mixed refrigerants within 30%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.12
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• pp.915-923
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• 2008

The performance experiments for a microchannel printed circuit heat exchanger (PCHE) of high-performance and high-efficiency on the two technologies of micro photo-etching and diffusion bonding were performed in this study. The microchannel PCHE were experimentally investigated for Reynolds number in ranges of 100 $\sim$ 700 under various flow conditions in the hot side and the cold side. The inlet temperatures of the hot side were conducted in range of $40^{\circ}C\;{\sim}\;50^{\circ}C$ while that of the cold-side were fixed at $20^{\circ}C$. In the flow pattern, the counter flow was provided 6.8% and 10 $\sim$ 15% higher average heat transfer rate and heat transfer performance than the parallel flow, respectively. The average heat transfer rate, heat transfer performance and pressure drop increases with increasing Reynolds number in all the experiment. The increasing of inlet temperature in the experiment range has not an effect on the heat transfer performance while the pressure drop decrease slightly with that of inlet temperature. The experimental correlations to the heat transfer coefficient and pressure drop factor as a function of the Reynolds number have been suggested for the microchannel PCHE.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.4
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• pp.188-198
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• 2003

R410A and R407C are considered to be alternative refrigerants of R22 for the air-conditioners. An experimental study is carried out to investigate the effect of the change of mass flow rate on the characteristics of heat transfer and pressure drop in three row slit finned-tube heat exchanger for R407C, R410A and R22. R407C, a non-azeotropic refrigerant mixture, exhibited a quite different condensation phenomenon from those of R22 and R410A and its condensation heat transfer coefficient was much lower than that of R22 and R410A. On the other hand, the condensation heat transfer coefficient of R410A, near-azeotropic refrigerant mixture, was a little higher than that of R22. R410A also showed the lowest condensation pressure drop across the test section. For all refrigerants, the condensation heat transfer coefficient and pressure drop increase as the mass flux increases. The condensation heat transfer coefficient correlation proposed by Kedzierski shows the best agreement with the experimental data within $\pm$20%.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.283-292
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• 1999

Temperature prediction model was developed for on-line application to plate rolling mills of POSCO. The adequate boundary conditions of heat transfer coefficients were obtained by comparing the predicted temperature with the measured temperatures taken by measuring system in plate rolling mill of POSCO. In obtaining the boundary condition which minimize the mean and standard deviation of the difference between prediction and measurement, orthogonal array for experimental design was used to reduce the calculation time of large data set. To predict the temperature drop at four edge of plate in one dimensional model, the energy change by heat transfer though directions perpendicular to thickness direction was treated like that by deformation. And the heat transfer through four edge directions was inferred from that through thickness direction with two coefficients of depth and severity of temperature drop at the edge. The boundary condition for the depth and severity of temperature drop were also determined using the measured temperature.

• Journal of Environmental Science International
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• v.6 no.4
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• pp.391-397
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• 1997

The study was carried out to demonstrate the superiority of used packing in view of energy saving and efficiency of mass transfer, comparing with conventional packing. The results are as follows : 1. Owing to low Pressure drop under high load. 25mm NSW-ring, pp. can cause energy saving 2. The unique magnitudes of used packing are as follows $C_G$=5.78, m=0.67, n=0.46 3. Used packing can make high efficiency including energy saving because of low pres sure drop per the number of transfer unit. To rate the characteristic of packing, It should be carried out that the measurement of pressure drop per packing height and per the number of transfer unfit. This study demonstrated the superiority of used packing by carring out above experiment and could be used as basic reference for design and predicting efficiency of packing tower which is tilled with same packing.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.37-42
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• 2003

An experiment was performed to study heat transfer characteristics between corrugated heat exchanger and flat plate type one. While heat capacity(13.86kW) was provided constantly and the flow speed was varied from 2.8 to 17.9m/s, The temperature and the pressure drop were measured. Furthermore, Heat transfer coefficient, Colburn factor and Nusselt number were calculated using them. With increase of the flow speed for both exchangers, the coefficient and the pressure drop increased, but Colburn factor decreased. The coefficient, pressure drop and Colburn factor of the corrugated type were all higher than those of the flat one, which is due to the flow interruption with recirculation and reattachment of the corrugated type. The empirical correlations of Nusselt number were suggested for the tested two heat exchangers.

• Journal of Welding and Joining
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• v.13 no.2
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• pp.115-121
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• 1995

As the metal transfer in the GMAW process affects the weld quality and productivity, the mechanism of molten formation and detachment has been investigated at various welding conditions. The force balance and pinch instability models have been widely used to analyze the metal transfer in the globular and spray modes, respectively A new approach is proposed in this work by minimizing the energy of molten drop system. Effects of the surface tension, gravity, electromagnetic and drag forces are considered with no presumed molten drop geometry. Effects of various welding conditions on the metal transfer are explained. The results show that the proposed mode can be applied to the globular and spray transfer modes. When compared with other models, results of the proposed model show better agreements with the available experimental data, which demonstrates the validity of the present model.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.522-530
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• 2004

Single-phase heat transfer coefficients and pressure drops of R-718 were measured in smooth, horizontal copper tubes with inner diameters of 3.36 ㎜, 5.35 ㎜. 6.54 ㎜ and 8.12 ㎜, respectively. The experiments were conducted in the closed loop, which was driven by a magnetic gear pump. Data are presented for the following range of variables : Reynolds from 1000 to 20000. Single-phase heat transfer coefficients increased by 10∼30 % as the inner diameter of tube was reduced and it was found that a well-known previous correlation, Gnielinski's correlation was not suitable for the small diameter tubes. But the pressure drop in the small diameter tubes have been shown slightly deviations with Blauius' correlation. Based on an analogy between heat and mass transfer. the new heat transfer correlation is proposed to predict the experimental data successfully.