• 설비공학논문집
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• 제17권4호
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• pp.347-354
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• 2005

This paper compared vertical temperature distribution between the existing balcony model without ventilator facilities and the improved balcony model with ventilator facilities using differential equation. As the air inside of balcony is heated by solar radiation this heated air is not exhausted in the existing balcony, remaining stagnant. The air temperature distribution was $26.7{\sim}29.3^{\circ}C$ in balcony without natural ventilator system. This heated air affected the rising air temperature of adjacent spaces such as living room and bedroom in the existing balcony. But, as the heated air inside of the improved balcony model is exhausted through natural ventilator facilities in summer, the air temperature in balcony has fallen. The air temperature distribution in improved balcony was $24.8{\sim}26.7^{\circ}C$ for the inlet air speed of 1 m/s and $24.6{\sim}26.7^{\circ}C$ for the inlet air speed of 3 m/s. The energy consumption of the improved balcony is 2.5 times less than of the existing balcony. The improved balcony with the closed damper makes a roll as the existing balcony in the aspect of the heating effect. When the heated air in the improved balcony is supplied, the air temperature is raised and the ventilation effect in adjacent spaces was improved.

• International Journal of Air-Conditioning and Refrigeration
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• 제6권
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• pp.158-167
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• 1998

Natural convection heat transfer in a rectangular enclosure is investigated numerically for low aspect ratio(height/width) cavities. Numerical results are obtained for aspect ratios between ${10}^{-2}$ and ${10}^0$, Rayleight numbers from ${10}^3$ to ${10}^7$ and Prandtl numbers from 10$^{-2}$ to 10$^3$. Results are compared with existing analytical and experimental results. A heat transfer correlation is developed to predict the mean Nusselt number as a function of the three governing dimensionless parameters: Rayleigh number, aspect ratio and Prandtl number.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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• pp.376-381
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• 2012

Natural gas is converted in to LNG by chilling and liquefying the gas to the temperature of $-162^{\circ}C$, when liquefied, the volume of natural gas is reduced to 1/600th of its standard volume. This gives LNG the advantage in transportation. The pressure dorp of the cascade liquefaction cycle was investigated and simulated using HYSYS software. The simulation results showed that the pressure drop in the LNG heat exchanger is set to 50 kPa considering the increase in the compressor work of cryogenic cascade liquefaction cycle.

• 설비공학논문집
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• 제6권3호
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• pp.315-324
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• 1994

The energy recovery efficiency(ERE) of an aquifer thermal energy storage system was calculated using curvilinear coordinate. The results of the calculation were compared with the experimental results, and agreed within 11% of the discrepancy. The variation of ERE was investigated as a function of the underground water natural velocity, the amount of the stored energy, and period of the energy recovery. The slower the natural velocity and shorter the recovery period, the higher ERE was yielded. Also it was found that increase in the amount of energy storage yields higher ERE, and carries out less influential ERE to the natural velocity. Reiterative usage of the aquifer as a thermal storage tends to gradually increase ERE. The result of this study implements that the aquifer thermal energy storage system is suitable for large cooling/heating loads, such as district cooling/heating.

• 설비공학논문집
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• 제12권5호
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• pp.476-485
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• 2000

This study numerically investigates thermal comfort in a space cooled by the floor-supply air conditioning system, in which three different supply-return locations, one floor supply-ceiling return and two floor supply-floor returns, are treated. A complementary experiment is peformed to validate the present numerical analysis, and the prediction agrees favorably with the measured data. In the numerical procedure, a simplified model mimicking the inlet flow through the diffuser is developed for efficient simulations. The calculated results show that the ceiling return type is far better in thermal comfort than the floor return ones within the extent of this study, which seems to be caused by effective vertical penetration of the supply air against natural convection. It is also revealed that the arrangement of port locations in the floor supply-floor return system has insignificant effect on the cooling performance. For selecting a proper system, other characteristics including the heating performance should be accounted for simultaneously with the present estimation.

• 설비공학논문집
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• 제17권4호
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• pp.333-340
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• 2005

Horizontal air-jet effect has been utilized in some air conditioning systems in order to control the contaminated air indoor. In the present study, the flow and heat transfer of the contaminated air from a range hood system has been investigated with or without horizontal air-jet effect when the hood fan is on or off. For the present numerical experiment, PAT Flow code has been used. From the present numerical simulations, it has been shown that the air jet of a range hood generates coanda effect confining the contaminated air in a certain region. Furthermore, the qualitative relation between the flow rate of the capture air jet and the distribution pattern of the contamination has been discussed.

• International Journal of Air-Conditioning and Refrigeration
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• 제14권3호
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• pp.102-109
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• 2006

Experimental results for heat transfer characteristics and pressure gradients of HCs refrigerants R-290, R-600a, R-1270 and HCFC refrigerant R-22 during evaporating inside horizontal double pipe heat exchangers are presented. The test sections which has one tube diameter of 12.70 mm with 0.89 mm wall thickness, another tube diameter of 9.52 mm with 0.76 mm wall thickness are used for this investigation. The local evaporating heat transfer coefficients of hydrocarbon refrigerants were higher than that of R-22. The average evaporating heat transfer coefficient increased with the increase of the mass flux, with the higher values in hydrocarbon refrigerants than R-22. Hydrocarbon refrigerants have higher pressure drop than R-22. Those results from the investigation can be used in the design of heat exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.

• 설비공학논문집
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• 제13권3호
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• pp.160-166
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• 2001

A numerical analysis has been performed for natural convection in an air conditioner duct system. The governing equations were solved a finite volume method using a SIMPLE algorithm. In the calculation mode of duct, the room temperature was preserved at $25.0^{\circ}C$ and duct wall temperature had a temperature of 15, 20.0, 22.5, 23.75, 26.25, 27.5 30 and $35^{\circ}C$. The results of velocity vectors and contours have been represented for various parameters. Based on the numerical data, the relationships between temperature difference and flow rate into room was represented. In the case of $T_\gamma>T_\omega$, the equation for temperature difference and flow rate was $Q=0.0285\triangleT^0.4005$, and in the case of $T_\gamma>T_\omega$, the equation was $Q=0.0099\triangleT^0.4752$. The duct system has an important relation to room temperature and duct wall temperature.

• 설비공학논문집
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• 제13권11호
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• pp.1114-1124
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• 2001

The application of carbon dioxide as an attractive natural working fluid in air cooling and heating system is increasingly important in view of the CFC substitution problem. The thermal performance of compact evaporator was analyzed using section-by-section method. The effects of the two-dimensional nonuniformity of air flow through the evaporator is presented. The detrimental effect of the aid flaw nonuniformity on the thermal performance of the evaporator is found to be significant for many typical applications. It is shown that total heat transfer rate of evaporator using $CO_2$ is higher than that using R134a at the simulation conditions.

• 설비공학논문집
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• 제14권7호
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• pp.543-551
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• 2002

Gravity ventilators allow the escape of the warm air and air contaminants due to both (either) buoyancy and (or) convection. As a natural ventilation strategy, various gravity ventilators can be installed on the roof. Ventilation efficiency could be affected by various parameters, such as, area of openings, wind velocity and incidence angle, temperature difference between inside and outside, and shape of ventilator. Especially, the shape of roof gravity ventilator might be one of influencing factors for the effective ventilation. The window type gravity ventilators are frequently installed instead of general (standard) gravity ventilator. However, the ventilation efficiencies of them were not proved yet. To compare the ventilation efficiency, general type ventilator and two window type ventilators were numerically tested. Mean age of air, temperature and CO concentration were predicted by using commercial CFD code, AIRPAK (Ver. 2.0) with various conditions. The predicted result showed that general type ventilator is more effective for natural ventilation than window type ventilators.