• Journal of the Korean institute of surface engineering
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• v.25 no.2
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• pp.73-81
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• 1992

The composite coating of suspended inert particles $\alpha$-Al2O3 and copper from acid sulphate bath was investigated at the Rotating Disk Electrode. Effects of rotation speeds of electrode, physical properties of electrolyte, the size and concentration of suspended particles on the codeposition ratio of Al2O3 and the enhancement of mass transfer of copper ions were examined. Particularly, new experimental method for the measurement of the codeposition ratio was suggested and also the characteristics of the composite coating layer were measured by Rutherford Backscattering Spectrometry. Mass transfer of suspended particles system were increased up to 40% more than those of without suspended particles system. Optimum conditions of current density, hydrodynamics of RDE, and particles concentration showing maximum codeposition ratio were appeared in our experimental ranges. It was shown that the suspended inert particles were codeposited mainly near the surface of the composite coating layer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.10
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• pp.825-832
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• 2002

The present study investigated the enhancement of the absorption performance by the spring wrapped around the outer surface of the vertical falling film absorber tube. Heat and mass transfer enhancements were experimentally investigated, and flow visualization was performed to observe the wettability and flow pattern of the solution. The key experimental parameters were spring diameter (0.5, 1.0 mm) and spring pitch (1, 3, 10 mm), film Reynolds number (50~150), and concentration of LiBr-$H_2O$ solution (55, 60, 65 wt%). As the spring diameter was increased, the absorption mass flux, Sherwood number, Nusselt number, heat flux, and heat transfer coefficient were increased The Nusselt and Sherwood numbers showed the maximum at the spring pitch of 3mm, and the ratio of pitch to diameter of approximately 3 and 6 for the spring diamter of 0.5 mm, respectively.

• KSBB Journal
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• v.8 no.5
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• pp.417-423
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• 1993

The effect of moisture content of biocatalyst on the performance of a gas phase continuous bioreactor was investigated along with study on the mass transfer limitation. The biocatalysts whose moisture contents are 46.2% and 37.2%, respectively were prepared by immobilization of alcohol oxidase on Amberlite IRA-400, following by slow dehydration method, and packed into a column. Relative production rate (RPR), acetaldehyde composition ($X_p$) and conversion (X) of biocatalysts (37.2%) are better than those of biocatalysls (46.2%), and it was considered that these are attributed to the mass transfer enhancement in the gas phase compared with the aqueous phase.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.4
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• pp.534-541
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• 2008

This paper deals with the heat transfer characteristics of R-290 (Propane), R-600a (Iso-butane) and R-1270 (Propylene) as an environment friendly refrigerant and R-22 as a HCFC's refrigerant for evaporating. The experimental apparatus has been set-up as conventional vapor compression type refrigeration and air-conditioning system. The test section is a horizontal double pipe heat exchanger. Evaporating heat transfer measurements were performed for smooth tube with the outer diameters of 12.70, 9.52 and 6.35 mm and micro-fin tube 12.70 mm, respectively. For the smooth and micro-fin tubes measured in this study, the evaporating heat transfer coefficient was enhanced according to the increase of the mass flux and decrease of the tube diameter. The local evaporating heat transfer coefficients of hydrocarbon refrigerants were superior to those of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-1270. The average evaporating heat transfer coefficients in hydrocarbon refrigerants showed 20 to 28% higher values than those of R-22. Also, the evaporating heat transfer coefficients of R-22 in the tube diameter of the 12.70 mm smooth and micro-fin tube were compared. Generally, the local heat transfer coefficients for both types of tubes increased with an increase of the mass flux. The heat transfer enhancement factor (EF) between smooth and micro-fin tube varied from 1.9 to 2.7 in all experimental conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.12
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• pp.1113-1122
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• 2005

The experimental heat transfer coefficients have been measured for two-phase convective boiling in two circular microtubes with inner diameters of $430{\mu}m\;and\;792{\mu}m$. While the heat transfer was greatly affected by the heat flux in the low quality region, the mass flux played a role in the high quality region. The smaller microtube had greater heat transfer coefficients. When the heat flux is varied from $20kW/m^2\;to\;30kW/m^2\;at\;G=240kg/m^2s$, the difference between the average heat transfer coefficients of the test tube $A(D_i=430{\mu}m)$ and the test tube $B(D_i=792{\mu}m)$ changes from $32.5\%\;to\;52.1\%$. At $G=370kg/m2^s$, the difference between the average heat transfer coefficients changes from $47.0\%\;to\;53.8\%$. A new correlation for the evaporative heat transfer coefficients in microtubes was developed by considering the following factors; the laminar flow heat transfer coefficient of liquid-phase flow, the enhancement factor of the convective heat transfer, and the nucleate boiling correction factor. The correlation developed in this study predicts the experimental heat transfer coefficients within an absolute average deviation of $8.4\%$.

• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1159-1167
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• 2000

Particles in liquid-solid suspension flow might enhance or suppress the rate of heat transfer and turbulence depending on their size and concentration. The heat transfer characteristics of liquid-solid suspension in turbulent flow are not well understood due to the complexibility of interaction between solid particles and turbulence of the carrier fluid. In this study, the heat transfer coefficients of liquid-solid mixtures are investigated using a double pipe heat exchanger with suspension flows in the inner pipe. Experiments are carried out using spherical fly ash particles with mass median diameter ranging from 4 to $78{\mu}m$. The volume concentration of solids in the slurry ranged from 0 to 50% and Reynolds number ranged from 4,000 to 11,000. The heat transfer coefficient of liquid-solid suspension to water flow is found to increase with decreasing particle diameter. The heat transfer coefficient increases with particle volume concentration exhibiting the highest heat transfer enhancement at the 3% solid volume concentration and then gradually decreases. A correlation for heat transfer to liquid-solid flows in a horizontal pipe is presented.

• Journal of Power System Engineering
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• v.12 no.3
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• pp.19-25
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• 2008

This paper deals with the heat transfer and pressure drop characteristics of R-290 (Propane), R-600a (Iso-butane) and R-1270 (Propylene) as an environment friendly refrigerant and R-22 as a HCFC's refrigerant for condensing. The test section is a horizontal double pipe heat exchanger. Condensing heat transfer and pressure drop measurements were Peformed for 12.70 mm micro-fin tube and compared with the results in smooth tube. The local condensing heat transfer coefficients of hydrocarbon refrigerants were superior to those of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-600a. The average condensing heat transfer coefficients in hydrocarbon refrigerants showed 20 to 28% higher values than those of R-22. Hydrocarbon refrigerants have a higher pressure drop than that of R-22 with respect to refrigerant qualify and mass flux. Also, the condensing heat transfer coefficient and pressure drop of working fluids in smooth and micro-fin tube were compared. The heat transfer enhancement factor (EF) between smooth and micro-fin tube varied from 2.2 to 2.6 in all experimental conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.6
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• pp.533-540
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• 2000

Condensation heat transfer characteristics have been investigated experimentally when a water vapor is condensed on the outside of a horizontal copper tube in a condenser. This problem is of particular interest in the design of a LiBr-water absorption system. Hydrophilic surface modification was performed to increase the wettability on the copper tube. The optimum hydrophilic treatment condition using acethylene and nitrogen as reaction gas is also studied in detail. The results obtained indicate that the optimum reaction gas ratio of acethylene to nitrogen for hydrophilic surface modification was found to be 7 : 3 for the best condensation heat transfer. In the wide ranges of coolant inlet temperatures, and coolant mass flow rates, both the condensation heat transfer rate and the condensation heat transfer coefficient of a hydrophilic copper tube are increased substantially, compared with those of a conventional copper tube used in a condenser. It is also found that the condensation heat transfer enhancement by the hydrophilic surface modification still emains even after a hundred cycles of wet/dry processes.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.440-445
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• 2008

The present study was investigated the effect of the driving condition on the performance of a louver fin and tube type heat exchanger under frosting condition. Heat transfer rate and pressure drop by frost were experimentally investigated. Effects of the wet blub temperature and the shape of a fin on heat transfer performances has been also investigated. The key parameters were fin type(louver and corrugate fin) and the wet blub temperature of air (0.5, 1.0, $1.5^{\circ}C$). The heat transfer performance of the louver fin and tube type heat exchanger was higher by 0.89% than the corrugate fin type. As the wet blub temperature of air were increased, the heat transfer rate, pressure drop and mass of frost of three test models(Type A, B, C) were increased. Especially, the maximum heat transfer rate and maximum pressure drop were shown for the louver fin and tube type heat exchanger. As a experimental result, the enhancement factor(EF) of louver fin and tube type heat exchanger was $0.2{\sim}0.4$ due to the high pressure drop.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.8
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• pp.692-700
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• 2001

Flow boiling heat transfer coefficients(HTCs) of R22, R134a, R407C, and R410A were measured experimentally for a horizontal plain and a microfin tube. Experimental apparatus was composed of 3 main parts: a refrigerant loop, a water loop and a water-glycol loop. The test section in th refrigerant loop was made of a copper tube of 9.52 mm outer diameter and 1 m length for both tubes. The refrigerant was heated by passing hot water through an annulus surrounding the test section. Tests were performed at a fixed refrigerant saturation temperature of $5^{\circ}C$ with mass fluxes of 100~300 kg/$m^2$s. Test results showed that at similar mass flux the flow boiling HTCs of R134a were similar to those of R22 for both plain and microfin tube. HTCs of R407C were similar to those of R22 for a plain tube but lower than those of R2 by 25~48% for a microfin tube. And HTCs of R410A were higher than those of R2 by 20~63% for a plain tube and were similar to those of R22 for a microfin tube. In general, HTCs of a microfin tube were 1.8~5.7 times higher than those of a plain tube.