• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.12
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• pp.3317-3328
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• 1995

The objective of the present study is to predict the characteristics of heat and mass transfer around an evaporative condenser. Numerical calculations have been performed using multi-zone method to investigate heat transfer rate and evaporation rate with the variation of inlet condition(velocity, relative humidity and temperature) of the moist air, the flow rate of the cooling water and the shape of the condenser tube. From the results it is found that the profile of heat flux is the same as that of evaporation rate since heat transfer along the gas-liquid interface is dominated by the transport of latent heat in association with the vaporization(evaporation) of the liquid film. The evaporation rate and heat transfer rate is increased as mass flow rate increases or relative humidity and temperature decrease respectively. But the flow rate of the cooling water hardly affect the evaporation rate and heat flux along the gas-liquid interface. The elliptic tube which the ratio of semi-minor axis to semi-major axis is 0.8 is more effective than the circular tube because the pressure drop is decreased. But the evaporation rate and heat flux shown independency on the tube shape.

• International Journal of Air-Conditioning and Refrigeration
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• v.14 no.1
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• pp.19-27
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• 2006

The characteristics of heat transfer and pressure drop have been investigated experimentally during gas-cooling process of carbon dioxide. The results of this study are useful information in the design of a heat exchanger of $CO_2$ refrigerator. The test section consists of 6 series of copper tube, 4.15 and 2.18mm ID, respectively. The inlet temperature, the operating pressure, and the mass flux are varied in the range of $80{\sim}120^{\circ}C,\;{7\sim}10MPa,\;and\;400{\sim}1,900kg/m^2s$, respectively. The heat transfer coefficient of $CO_2$ is affected by temperature, inlet pressure, and mass flux of $CO_2$. At the maximum HTC, the temperature of $CO_2$ nearly accords with the psuedocritical temperature. It is found that the pressure drop is substantially affected by mass flux and inlet pressure of $CO_2$ . The results have been compared with those of previous work. The heat transfer correlation at the gas-cooling process has been also suggested which predicts within the error of 20%.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.2
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• pp.145-151
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• 2007

The evaporation heat transfer coefficient of $CO_2$(R-744) in a horizontal tube was investigated experimentally. The main components or 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 inner diameter of 4.57 mm. The experiments were conducted at mass flux of 200 to $500\;kg/m^2s$, saturation temperature of -5 to $5^{\circ}C$, and heat flux of 10 to $40\;kW/m^2$. The test results showed the heat transfer of $CO_2$ has a greater effect on nucleate boiling more than convective boiling. Mass flux of $CO_2$ does not effect nucleate boiling too much. 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 existing correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develope reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1137-1146
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• 2002

An experiment has been conducted on the flow and heat transfer characteristics of film coolant injected from a row of five holes with compound angle orientations of 35$^{\circ}$ inclination angle and 45$^{\circ}$ orientation angle. The Reynolds number based on the mainstream velocity and injection hole diameter 3.58${\times}$10$^4$. Three-dimensional velocity, film cooling effectiveness and heat transfer coefficient data are presented at three different mass flux ratios of 0.5, 1.0 and 2.0. Flow entrainment has been found between the vortices generated by adjacent injectants. The injectant with compound angle orientation entrains not only the mainstream boundary layer flow but also the adjacent injectant. Because of the flow entrainment, the injectant. With compound angle orientation is characterized by a single vortex while two bound vortices are usually observed in the case of simple angle injection. The strength of the secondary flow depends strongly on the mass flux ratio, which shows significant influence on the film cooling effectiveness and heat transfer coefficient.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.4
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• pp.503-510
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• 2011

Ammonia in water which is toxic to human, its concentration is regulated below 0.5 mg/L in drinking water. Current study aimed to develop appropriate models for ammonia stripping using hollow fiber membrane contactor. Two different models were developed during the study. Model 1 was assumed only free ammonia ($NH_3$) transfer in stripping process, whereas the Model 2 was assumed with total ammonia ($NH_3+{NH_4}^+$) transfer. Ammonium chloride ($NH_4CI$), sodium hydroxide(NaOH) were used to make ammonia solution, which was concentration of 25 mg as N/L at a pH of 10.5. The experimental conditions were such that, the liquid flow was in tube-side in upward direction and t he gas flow was on shell-side in downward direction a t room temperature. The experimental and modeling results showed that marginal difference were observed at low gas flux. However the difference between the both models and experimental value were increased when the gas flux was increased. The study concludes that the Model 1 with free ammonia is more appropriate when both models were compared and useful in ammonia stripping process at low gas flux.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.245-254
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• 2009

Efficiency of landfill liners system is usually evaluated based on leakage rate and mass flux. In this study, composite liner systems including the GCL(geosynthetic clay liner) composite liner, the Subtitle D liner, the Wisconsin NR500 liner, and the recently utilized double composite liner, which is a combination of the GCL composite liner and Subtitle D-type liner, have been examined. The leakage rate through circular and long defects in the geomembrane (GM) of the liner system was analyzed with the aids of analytical and numerical methods. For the mass flux criterion, contaminant transport through defects in the GM of landfill liners can be evaluated based on the calculated leakage rates. The diffusion rate of volatile organic compounds through intact landfill liners was evaluated by performing a one-dimensional numerical model. Cadmium and toluene were adoptted in the analyses as typical inorganic and organic substances, respectively, which will be chemical species encountered during landfill operation. The performance-based evaluation indicates that the double composite liner systems are superior to the other types of liner.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.2
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• pp.106-112
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• 2008

In this paper, the experimental results on evaporation heat transfer characteristics were reported for a micro-fin tube using $CO_2$. An experimental refrigerant loop had been established to measure the evaporation heat transfer coefficient and pressure drop of $CO_2$. Experiments were conducted for mass fluxes, heat fluxes, saturation temperatures and PAG oil concentrations. With increasing the heat flux and the saturation temperature, the evaporation heat transfer coefficient increased. At the higher mass flux, however, the exit vapor quality of the micro-fin tube was to be lower. The peak of the heat transfer coefficient was shifted toward low quality region. The evaporation pressure drop increased as the mass flux increased and the saturation temperature decreased. As PAG oil concentration increased, the evaporation heat transfer coefficient decreased and the dryout was delayed by oil addition.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1130-1137
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• 1988

Heat transfer characteristics of evaporative transpiration cooling was investigated experimentally in the range of coolant mass flux, 0.002kg/m$^{2}$.sec~0.015m$^{2}$.sec. Glass beads, sand and copper particles were used as porous media and distilled water was used as a conant. The existence of evaporation zone was confirmed on this experimental conditions and its length increases with increasing article size and with decreasing mass flux. In order to get the low surface temperature, porous materials with high thermal conductivity is preferred when the panicle sizes are same, and small particles with low porosity is effective in case of the same material. Due to the relatively small coolant mass flux, evaporative transpiration cooling system could be stable by the capillary effect.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2011-2017
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• 2023

Gas submerged jet is an outstanding thermohydraulic phenomenon in pool scrubbing of fission products during a severe nuclear accident. Experiments were performed on the hydraulic characteristics in the ranges of air mass flux 0.1-1400 kg/m²s and nozzle diameter 10-80 mm. The results showed that the dependence of inlet pressure on the mass flux follows a power law in subsonic jets and a linear law in sonic jets. The effect of nozzle submerged depth was negligible. The isolated bubbling regime, continuous bubbling regime, transition regime, and jetting regime were observed in turn, as the mass flux increased. In the bubbling regime and jetting regime, the air volume fraction distribution was approximately symmetric in space. Themelis model could capture the jet trajectory well. In the transition regime, the air volume fraction distribution loses symmetry due to the bifurcated secondary plume. The Li correlation and Themelis model showed sufficient accuracy for the prediction of jet penetration length.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
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• 2003.09a
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• pp.115-128
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• 2003

o What is the flux \ulcorner Flux is the transfer of a quantity per unit area per unit time. The quantities are mass, heat, moisture, momentum and pollutant in micrometeorology. Kinematic flux (Fluid). The reduction in wind speed due to frictional drag transfers momentum from the atmosphere to the surface, creating turbulence that mixes the air and transports heat and water from the surface into the lower atmosphere. (omitted)