The heat transfer coefficient and pressure drop during g as cooling process of CO(R-744)in a horizontal tube were investigated experimentally. The experiments were conducted withoutoil in the refrigerant loop. The mai...
The heat transfer coefficient and pressure drop during g as cooling process of CO(R-744)in a horizontal tube were investigated experimentally. The experiments were conducted withoutoil in the refrigerant loop. The main components of the refrigerant loop are a receiver, avariable-speed pump, a mass flow meter, a pre-heater and a gas cooler(test section). The waterloop consists of a variable speed pump, an isothermal tank, and a flow meter. The refrigerant,circulated by the variable-speed pump, condenses in the inner tube while water flows in theannulus. The gas cooler is 6000 mm in length, and it is divided into 12 subsections. The pressuredrop of CO in the gas cooler shows a relatively good agreement with those predicted byBlasius’s correlation. The local heat transfer coefficient of CO agrees well with the correlationby Bringer-Smith. However, at the region near Pseudo -critical temperature, the experimentsindicate higher values than the Bringer-Smith correlation. Based on the experimental datapresented in this paper, a new correlation to predict the heat transfer coefficient of supercriticalCO during in-tube cooling was developed. The deviation between the experimental values andthe values predicted by the new correlation is within 18%.
<正> Among the most widely used characteristics of asphalt mixture are Marshall stability and indirect tensile strength (ITS). This study examines importance of conditioning temperature and period before measuring...
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<正> Among the most widely used characteristics of asphalt mixture are Marshall stability and indirect tensile strength (ITS). This study examines importance of conditioning temperature and period before measuring these properties. Marshall specimens are conditioned by submerging in 60℃ water for 30 rain before loading. It was observed that ifthe specimen is cured in a lower (or higher) than normal lab temperature (25℃) before submerging, the measured values were not consistent. If the specimen is cured in lower temperature than normal, it should be submerged longer than 30 min at 60℃ for Mar- shall test. In ITS test on the specimens which were cured at different temperatures, it was found that keeping the temperature at 25℃ is very important in final result. Although there is no regulation specifying how long the specimen should be conditioned before testing, the specimen should be conditioned long enough time to secure it to be at 25℃. It was also found that if lab air temperature is lower or higher than normal, mixture was not properly cured, and test results were not reliable.
A robust approach for the derivation of closed-form Green’s functions is considered based upon a three level approximation procedure, which can give more accurate evaluation of the spatial Green’s fu
A robust approach for the derivation of closed-form Green’s functions is considered based upon a three level approximation procedure, which can give more accurate evaluation of the spatial Green’s fu
<正>Spraying is one of the most efficient methods for pesticide and insecticide control. Generally, Speed Sprayer (Air carrier sprayer) is used for spraying in Korea when Speed Sprayer is used but chemical deposit...
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<正>Spraying is one of the most efficient methods for pesticide and insecticide control. Generally, Speed Sprayer (Air carrier sprayer) is used for spraying in Korea when Speed Sprayer is used but chemical deposition amount on crops is only 20% of total spraying amount. Agricultural chemicals which fail to reach the crops not only cause environmental contamination but losses of agricultural chemicals by lower deposition efficiency. In this research, laboratory test was carried out to determine the optimum design conditions of electrostatic agricultural nozzles for orchard applications. Parameters studied were type of electrode, the diameter of nozzle, and tilt angle of metal leaf. The results showed that the coverage area ratios and number of droplets for electrostatic nozzle were increased proportionally with the charging voltage. However, it appeared those electrical potentials higher than 4.5kV caused electrical discharge between nozzle body and electrode. Electrostatic nozzles resulted in significantly higher coverage area ratios than that of conventional nozzles. The optimum nozzle diameter and charging voltage in pin type electrode were found to be 0.59 mm and 4.0 kV, respectively.
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