• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.4
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• pp.552-558
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• 2002

Differentiated services (DiffServ) architecture defines a new framework for the support of quality of service (QoS) in IP-based networks. RIO has received the most attention among all the active queue management mechanisms proposed for assured service in DiffServ environment. The paper proposed the enhanced RIO which could alleviate the impact of flow's packet sire on the realized throughput. The simulation results indicate that this mechanism, when combined with TSW as traffic conditioner, provide better throughput assurance and fair distribution of excess bandwidth independent of packet size of flows in case of well-provisioned network environment.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.560-563
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• 1997

Sound intensity method is well known as a visualization technique of sound field and sound propagation in noise control. Sound intensity is a vector quantity that describes the magnitude and the direction of net flow of acoustic energy at a given position. The current measuring method is expensive and difficult to identify the noise source exactly. In this paper, we have studied the noise source identification and the characteristics of noise source of rotary compressor for air conditioner using complex sound intensity method. The new method for instantaneous sound intensity is also proposed and it is useful for transient state and steady state. The criteria of these states select auto correlation coefficient. The advantage, simplicity and economic attribution of this method are verified by analyzing the characteristics of noise source with instantaneous sound intensity compared to mean sound intensity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.960-963
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• 2003

Sound intensity method is well known as a visualization technique of sound field and sound propagation in noise control. Sound intensity is a vector quantity that describes the magnitude and the direction of net flow of acoustic energy at a given position. The current measuring method is expensive and difficult to identify the noise source exactly. In this paper, we have studied the noise source identification and the characteristics of noise source of rotary compressor for air conditioner using complex sound intensity method. The new method for instantaneous sound intensity is also proposed and it is useful for transient state and steady state. The criteria of these state, select auto correlation coefficient. The advantage, simplicity and economic attribution of this method are verified by analyzing the characteristics of noise source with instantaneous sound intensity compared to mean sound intensity.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.6-8
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• 2002

Generally in solar air conditioning system, the diode rectifier is used to build up DC link voltage from AC source. The diode rectifier is simple and cheap but it brings out the problems of low power factor and plentiful harmonics at the AC source. Also It can degrade the utilization rate of solar energy because the reverse of power flow cannot be made. Hence, in this paper to overcome the peak power problems in summer and to endure good AC input characteristics, solar air conditioning system using the PWM converter is proposed. A high input power factor of 97[%] and an efficiency of 98[%] are also obtained. The harmonic guide lines of proposed rectifier is no interfered with inverter switching, resulting in a simple, reliable and low cost ac to dc converters in comparison with the boost type current improving circuits.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.1 no.1
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• pp.1-14
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• 2000

This paper is concerningon the development of cross-flow fan (CFF) for vehicles. CFF is widely usedhome-appliance products. This work mainly Intends developing CFF only for an automobile. In order to do that, new design involving blade shapes is proposed with enough performance for the operation. Spacially three steeps are proceeded for blade design. injection conditions for manufacturing, and capacity test for fluid mechanics. The present methodologies are to find optimal design for the blades and conditions for the injection process. This project has continued since last two years and finally succeeded.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.103-111
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• 2024

Axial-flow fans are used to transport fluids in relatively low-pressure flow regimes, and a variety of design variables are employed. The tip geometry of an axial fan plays a dominant role in its flow and noise performance, and two of the most prominent flow phenomena are the tip vortex and the tip leakage vortex that occur at the tip of the blade. Various studies have been conducted to control these three-dimensional flow structures, and winglet geometries have been developed in the aircraft field to suppress wingtip vortices and increase efficiency. In this study, a numerical and experimental study was conducted to analyze the effect of winglet geometry applied to an axial fan blade for an air conditioner outdoor unit. The unsteady Reynolds-Averaged Navier-Stokes (RANS) equation and the FfocwsWilliams and Hawkings (FW-H) equation were numerically solved based on computational fluid dynamics techniques to analyze the three-dimensional flow structure and flow noise numerically, and the validity of the numerical method was verified by comparison with experimental results. The differences in the formation of tip vortex and tip leakage vortex depending on the winglet geometry were compared through a three-dimensional flow field, and the resulting aerodynamic performance was quantitatively compared. In addition, the effect of winglet geometry on flow noise was evaluated by numerically simulating noise based on the predicted flow field. A prototype of the target fan model was built, and flow and noise experiments were conducted to evaluate the actual performance quantitatively.

• Journal of Bio-Environment Control
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• v.5 no.2
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• pp.160-166
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• 1996

Objective of this study was to investigate the effects of all current speed on the microclimates above and inside the plug stand under artificial light. Maximum air temperature appeared near the top of the plug stand. Difference in air temperature inside the plug stand increased with the decreasing air current speed. Difference in relative humidity(DRH) to the relative humidity at the Inlet of the main air flow conditioner Inside and above the plug stand decreased with the increasing air current speed. Relative humidity inside the plug stand was 10-15% higher than that above the plug stand. DRH inside a stand of plug at air current speed of 0.3m s$^{-1}$ was about two times as many as that at air current speed of 0.9 m s$^{-1}$ . DRH inside the plug stand was 2.8-6.5% higher at LAI of 2.6 than that at LAI of 0.5. Gradient for the vapour pressure deficit was distinctly appeared at the low air current speed. Direction of vapour pressure flux is from the medium surface upwards. Difference in vapour pressure(DVPD) to the vapour pressure deficit at the inlet of the main air flow conditioner inside and above the plug stand decreased with the increasing height above the medium surface. DVPD inside the plug stand was 0.3-0.4㎪ higher at air current speed of 0.9m s$^{-1}$ than that at air current speed of 0.3m s$^{-1}$ . Results for the effects of air current speed on the relative humidity and vapour pressure deficit indicated that the microclimates above and inside the plug stand at the rear region in plug trays were slightly unfavorable compared to those at middle region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.821-828
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• 2012

Increasing heat generation in CPUs can hamper effective recirculation and by-pass because of the large temperature difference between the exhaust and the intake air through a server room. This increases the overall temperature inside a data center and decreases the efficiency of the data center's cooling system. The purpose of the data center's cooling system is to separate the intake and exhaust air by controlling the computer room air-conditioner(CRAC). In this study, ICEPAK is used to conduct a numerical analysis of a data center's cooling system. The temperature distribution and the entire room are analyzed for different volumetric flow rates. The optimized volumetric flow rate is found for each CPU power. The heat removal and temperature distribution for CPU powers of 100, 120, and 140 W are found to be the best for a volumetric flow rate of $0.15m^3/s$. The numerical analysis is verified through RTI indicators, and the results appear to be the most reliable when the RTI value is 81.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.8
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• pp.5045-5050
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• 2015

As modern houses are constructed with high-density and high-insulation, there is benefit to reduce energy consumption, but there are many side effects raised from polluted air. To solve the problem, a ventilation system is used to improve a indoor air quality. In this study, we tested the parallel flow type heat exchanger used in a heat exchanger of an automotive air conditioner. And we experimentally estimate ventilation performance of HRV(heat recovery ventilator) with heat-pipe according to working fluid filling quantity and ventilation. The working fluid was R22, which was filled from 40 to 60 (%vol.) by 10(%vol.). Ventilation based on the front velocity was measured from 0.3 m/s to 1.5 m/s by 0.3 m/s intervals. Refrigerant filling quantity with the highest efficiency was found to depend on the ventilation. From this study the optimal refrigerant filling quantity in accordance with the ventilation of the detachable heat pipes was found experimentally.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.435-449
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• 1995

In this paper, pressure drop through a capillary tube is modeled to determine the length of a capillary tube for a given set of conditions. HCFC-22 and its alternatives, HFC-134a, R407B, and R410A are used as working fluids. The conditions on which the model is tested are as follows : condensing temperature; 40.0, 45.0, 50.0, $55.0^{\circ}C$, degree of subcooling;0.0, 2.5, $5.0^{\circ}C$, capillary tube exit condition;choked flow, capillary tube diameter;1.2~2.4mm, mass flow rate;5.0~50.0g/sec. The results justify the use of Stoecker's model which yields the results very close to the values in ASHRAE handbook. While McAdams' method yields much better results than Duckler's in calculating the viscosity of the fluid in 2-phase, the friction factor suggested by Stoecker seems to be the best for capillary tubes of large diameter used in residential air conditioners. For each refrigerant, 372 data with various variables are calculated by the model. The results show that capillary tube length varies very uniformly with changes in condensing temperature and degree of subcooling. Based on this fact, regression analysis is performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and degree of subcooling. Thus determined correlation yields a mean deviation of 2.36% for 1,488 data, showing an excellent agreement.