• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.10
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• pp.852-859
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• 2003

R407C is considered as an alternative refrigerant of R22 for air conditioners. An experiment was carried out to investigate the characteristics of the evaporation heat transfer and pressure drop for refrigerant R407C flowing in a fin-and-tube heat exchanger used for commercial air-conditioning unit. The experimental data were useful in analyze the effects of the temperature glide and superheat for R407C. Test were conducted at the conditions of inlet refrigerant evaporation temperature of 7$^{\circ}C$, inlet air relative humidity of 50%, and refrigerant mass fluxes varying from 150 to 250 kg/m$^2$s. Representative results show that the heat exchanger performance for R407C evaporation is significantly affected by the change of the flow pattern from two-phase to super-heated vapor flow.

• Journal of the Korean Ceramic Society
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• v.30 no.8
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• pp.678-684
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• 1993

Alumina composite membranes were prepared by chemical vapor deposition and evaporation-oxidation process. For CVD process, deposition was carried out using aluminum-tri-isopropoxide at 35$0^{\circ}C$, 2 torr by heterogeneous reaction, and for evaporation-oxidation process, alumina composite membranes were prepared by evaporation of aluminum and dry oxidation at 80$0^{\circ}C$. As deposition time increases, water flux and N2 gas permeability of the composite membranes prepared by both processes were reduced. Applying gas permeation model, permeability and cracking possibility of top layer were evaluated.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.3
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• pp.297-305
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• 2005

The evaporation heat transfer coefficient of $CO_2$ (R-744) in a horizontal 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 consists of a smooth. horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500\;kg/m^{2}s$. saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$. and heat flux of 10 to $40\;kW/m^2$. The test results showed the evaporation heat transfer of $CO_2$ has greatly 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 heat transfer coefficient of $CO_2$ is very larger than that of R-22 and R-134a. In making a comparison between test results and existing correlations. the present experimental data are the best fit for the correlation of Jung et al. But it was failed to predict the evaporation heat transfer coefficient of $CO_2$ using by the existing correlation. Therefore. it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.4
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• pp.167-174
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• 2005

The evaporation heat transfer coefficient of $CO_2$ (R-744) in a horizontal 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 consists of a smooth horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500kg/m^2s$, saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$, and heat flux of 10 to $40kW/m^2$. The test results showed the evaporation heat transfer of $CO_2$ has greater effect on nucleate boiling than convective boiling. The evaporation heat transfer coefficient of $CO_2$ is highly dependent on the vapor quality, heat flux and saturation temperature. The evaporation heat transfer coefficient of $CO_2$ is very larger than that of R-22 and R-134a. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Jung et al. But the existing correlations failed to predict the evaporation heat transfer coefficient of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• Journal of ILASS-Korea
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• v.12 no.1
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• pp.30-37
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• 2007

Dimethyl ether (DME) as an alternative fuel for compression ignition engine was investigated by measuring spray development processes, injection rate profiles, engine performance, and exhaust emission characteristics. The results of DME fueled engine were compared with those obtained by fueled with diesel. The experimental results showed that DME has approximately 0.03ms shorter injection delay and higher maximum injection rate than those of diesel fuel at a constant injection pressure of 50MPa. The spray visualization indicates that DME has shorter spray tip penetration due to its low density and faster evaporation. The combustion characteristics of DME operated engine provided faster ignition delay and three times shorter combustion duration. It is believed that the better evaporation and atomization characteristic of DME contributes the faster combustion. At all operating condition, soot emission was not detected due to the clean combustion of DME.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.5B
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• pp.445-458
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• 2010

The effects of geographical and climatic factors on annual and monthly pan and Penman evaporation were analyzed. 52 climatological stations were selected and trend analyses were performed. Furthermore, cluster analysis and multiple linear regression analysis were performed to understand the effects of geographical and climatic factors on pan and Penman evaporation. Based on stepwise multiple linear regression analysis, annual pan evaporation is proved to be mainly controlled by urbanization as geographical factor, and annual pan evaporation is also controlled by temperature, relative humidity, wind speed, and solar radiation as climatic factor. Especially wind speed is considered to be most significant climatic factor which affects pan evaporation. Meanwhile, Penman evaporation is not affected by geographical factors but it is affected by climate factors such as temperature, relative humidity, wind speed, and solar radiation except precipitation. Furthermore, the study results show that only proximity to coast affects pan evaporation trend on July; however, geographical and climatic factors do not affect pan evaporation trends in annual basis and monthly basis (January, April, and October). On the other hand, Penman evaporation trends were not affected by geographical factors in annual and monthly basises.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1078-1087
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• 2003

Kimchi refrigerator is a household electric appliance developed with the wholly domestic technology for maturing and keeping kimchi. However, the principle of keeping is not yet revealed obviously. This numerical study has been conducted to investigate the flow and heat transfer characteristics in a kimchi refrigerator. The effects of arrangement variation of a evaporation tube are examined. Also, the heat transfer characteristics through the insulation material are discussed in detail. The flow and temperature field was simulated using the commercial code of CFX-5.3. A natural convection flow is formed through about 5/6 region from the bottom within the keeping space and accordingly, the 90% region of kimchi containers satisfies the temperature requirement with 0$\pm$0.5$^{\circ}C$. The stagnant flow exists in the upper 1/6 region of the keeping space and accordingly, the stratified high temperature distributions appear in the upper region of kimchi containers. The upward shift of the start location of a evaporation tube improves the temperature concentration toward $0^{\circ}C$ but the pitch variation is of no effect. The heat fluxes on the insulation surfaces show two-dimensional distributions with being higher toward the center. Through the variation of insulation thickness, 3.5% saving of insulation material is obtained under the same heat transfer rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.12 s.243
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• pp.1360-1368
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• 2005

This study investigates the characteristics of spray, such as evaporation rate and spray trajectory, for a 4-hole injector which is applied to a 4-valve motorcycle gasoline engine. Three dimensional, unsteady, compressible flow and spray within the intake-port and cylinder have been simulated using the VECTIS code. Spray characteristics were investigated at 6000 rpm engine speed. Furthermore, we visualized fuel behavior in the intake-port using a CCD camera synchronized with a stroboscope in order to compare with the analytical results. Boundary and intial conditions were employed by complete 1-D simulation of the engine using the WAVE code. Fuel was injected into the intake-port at two time intervals relative to the position of the intake valves so that the spray arrived when the valves were closed and fully open. The results showed that the trajectory of the spray was directed towards the lower wall of the port with injection against the closed valves. With open valve injection, a large portion of the fuel was lifted by the co-flowing air towards the upper half of the port and this was confirmed by simulation and visualization.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.4
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• pp.290-299
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• 2008

Evaporation heat transfer characteristics of $CO_2$/propane mixtures in horizontal smooth and micro-fin tubes have been investigated by experiment. The experiments were carried out for several test conditions of mass fluxes, heat fluxes, compositions of $CO_2$/propane refrigerant mixtures and tube geometries. Direct heating method was used for supplying heat to the refrigerant where the test tube was uniformly heated by electric current which was applied to the tube wall. Heat transfer coefficient data during evaporation process of $CO_2$/propane mixtures were measured for 5 m long smooth and micro-fin tubes with outer diameters of 5 mm, respectively. The tests were conducted at mass fluxes of 318 to 997 $kg/m^2s$, heat fluxes of 6 to 20 $kW/m^2$ and for several mixture compositions (100/0, 75/25, 50/50, 25/75, 100/0 by wt% of $CO_2$/propane). The differences of heat transfer characteristics between smooth and micro-fin tubes for various compositions of $CO_2$/propane refrigerant mixtures and the effect of mass flux, and heat flux on enhancement factor (EF) and penalty factor (PF) were presented.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2172-2174
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• 2005

MgO has been used as the material of the protecting layer for AC PDP. AC PDP is influenced by characteristics of the surface glow discharge on the MgO thin film. Because MgO thin film is practically discharge electrodes, the discharge characteristics of MgO thin film should be varied with the method of deposition. In this study, changing order and time of deposition, we use electron beam evaporation system and R.F reactive magnetron sputtering system in the MgO deposition. Particularly, after using electron beam evaporation system, we use R.F. reactive magnetron sputtering system in the MgO deposition, then we could get lower amount of charge and higher luminance efficiency than only using electron beam evaporation system.