• 한국유체기계학회 논문집
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• 제4권3호
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• pp.39-45
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• 2001

It is reported recently that the pump head deterioration near the best efficiency point, from single-phase flow to the choke due to air entrainment became less in a screw-type centrifugal pump than in a general centrifugal pump. Moreover, at a narrow tip clearance, the pump head became partially higher in two-phase flow than that in single-phase flow. However, the internal pressure fluctuations on this pump due to air entrainment have not been studied yet. For that reason, we have examined the influences of void fraction, flow coefficient and impeller tip clearance on pressure fluctuations in the casing. The void fraction became larger, the influence of tip clearance on pressure distribution became less.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.221-221
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• 2000

The heat exchange part in a modern multi-type air-conditioning system employs multiple-pass heat exchangers. The heat-transfer performance of an each pass in such an exchanger depends strongly on the length of the two-phase region and the mass flow of the refrigerant. The total length and diameters of the pipes, the exit conditions, and the arrangement of each pass as well as the geometrical shape of the distributor at the branching sections are considered to be major factors affecting the heat-transfer performance. The refrigerant commonly used in these systems is HCFC-22. The two objectives of this paper are to investigate the characteristics of the refrigerant flow rate and the superheat in the evaporator of a multi-type air-conditioning system for a single or simultaneous operating conditions and to control the superheat and the refrigerant flow rate of the evaporator.

• 한국가시화정보학회지
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• 제4권2호
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• pp.81-87
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• 2006

In this paper, we present flow patterns around and performance of an air-flow separator by using the numerical analysis. With this separator, particles of different density are to be separated by using the drag force from the air flow. The low-density particles are designed to be separated by using inhalation through holes on a rotating drum. To obtain the flow informations needed for determining the proper design parameters, we have performed numerical simulations by using a commercial code, ANSYS CFX. Various parameter set was tested and it was found that depending on the design of drums there exist critical parameter set regarding the attachment of light particles on the drum, which is prerequisite for the separation of materials. We present here the possibility of using the present design in separation of particles mixed in the clod for use in recycling.

• 한국기계가공학회지
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• 제13권4호
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• pp.113-120
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• 2014

To ventilate indoor spaces, axial single-blade fans are widely used in various areas, such as schools, houses, offices, and restaurants. Recently, axial single-blade fans were developed to realize energy efficiency and noise reduction improvements. Here, an experimental study of the air flow characteristics of an axial dual-blade fan is conducted. The characteristics of the axial dual-blade fan were tested via an air flow analysis and with prototypes. For the performance of the fan, the flow rate, power consumption, and noise were evaluated. The result showed that the axial dual-blade fan uses less power and produces less noise in comparison with an axial single-blade fan.

• 한국가시화정보학회지
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• 제16권3호
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• pp.59-64
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• 2018

Numerical simulations were carried out to analyze the flow characteristics of the wind tunnel. Flow field characteristics with velocity uniformity at the test sections are largely affected by inlet conditions of air flow rate and temperature. Axial average velocity of the flow field inside the test area was almost linearly decreased by 0.026% each 1m. The uniformity distributions of axial velocity showed the highest reduction rate of about 24% between nozzle outlets 1 ~ 2m. In addition, average velocity and the uniformity are increased with air temperature in the wind tunnel due to density variation. The results of this paper are expected to be useful for the basic design of wind tunnel and to be used for efficient design.

• 한국전산유체공학회지
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• 제17권4호
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• pp.93-102
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• 2012

Once the condensation of water vapor in moist air around a thin airfoil occurs, liquid droplets nucleate. The condensation process releases heat to the surrounding gaseous components of moist air and significantly affects their thermodynamic and flow properties. As a results, variations in the aerodynamic performance of airfoils can be found. In the present work, the effects of upstream Mach number and thickness ratio of airfoil on the transonic flow of moist air around a thin airfoil are investigated by numerical analysis. The results shows that a significant condensation occurs as the upstream Mach number is increased at the fixed thickness ratio of airfoil($\epsilon$=0.12) and as the thickness ratio of airfoil is increased at the fixed upstream Mach number($M_{\infty}$=0.80). The condensate mass fraction is also increased and dispersed widely around an airfoil as the upstream Mach number and thickness ratio of airfoil are increased. The position of shock wave for moist air flow move toward the leading edge of airfoil when it is compared with the position of shock wave for dry air.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.304-309
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• 2008

The heating and cooling performances of system multi-air conditioner for various refrigerant flow rates with high-head and long-line conditions are experimentally investigated. The maximum head and tube length were 110 m and 1000 m, and the two different adjustments of refrigerant flow rates were +20 % and -20 %, respectively. The experimental system was composed of 4 outdoor units with module systems, and 13 indoor units which were joined with the mode change unit by single-tube circuit. Field tests without indoor and outdoor temperature control were performed in a general office building with two different refrigerant flow rates. Especially, the oil level in the compressor was normally maintained at the safety zone. Experimental results were prepared on the p-h diagram.

• Journal of Mechanical Science and Technology
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• 제17권3호
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• pp.429-439
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• 2003

Counter-current two-phase flows of air- water in narrow rectangular channels with offset strip fins have been experimentally investigated in a 760 mm long and 100 mm wide test section with 3.0 and 5.0 mm gap widths. The two-phase flow regime, channel-average void fractions and two-phase pressure gradients were studied. Flow regime transition occurred at lower superficial velocities of air than in the channels without fins. In the bubbly and slug flow regimes, elongated bubbles rose along the subchannel formed by fins without lateral movement. The critical void fraction for the bubbly-to-slug transition was about 0.14 for the 3 mm gap channel and 0.2 for the 5 mm gap channel. respectively. Channel-average void fractions in the channels with fins were almost the same as those in the channels without fins. Void fractions increased as the gap width increased, especially at high superficial velocity of air. The presence of fins enhanced the two-phase distribution parameter significantly in the slug flow, where the effect of gap width was almost negligible. Superficial velocity of air dominated the two-phase pressure gradients. Liquid superficial velocity and channel gap width has only a minor effect on the pressure gradients.

• 한국안전학회지
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• 제27권5호
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• pp.35-41
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• 2012

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to complement the previous experimental results of the bluff body stabilized flames [1]. For both fuel ejection configurations against an oxidizer stream, the flame stability was affected mainly by vortex structure and mixing field near bluff body. FDS(Fire Dynamic Simulator) based on the LES(Large Eddy Simulation) was employed to clarify the isothermal mixing characteristic and wake flow pattern around bluff body. The air used atmosphere and the fuel used methane. The result of counter flow configuration shows that the flow field depends on air velocity but the mixing field is influenced on the fuel velocity. At low fuel velocity the fuel mole fraction is below the flammable limit and hence the mixing is insufficient to react. Therefore, as the result, the flame formed at low fuel velocity is characterized by non-premixed flames. For the flow field of co-flow configuration, flame stability was affected by fuel velocity as well as air velocity. the vortex generated by fuel stream has counter rotating direction against the air stream. Therefore, the momentum ratio between air and fuel stream was important to decide the flame blow out limit, which is result in the characteristic of the partially premixed reacting wake near extinction.

• 한국유체기계학회 논문집
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• 제9권3호
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• pp.36-43
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• 2006

Recently, micro hydropower and it's useful utilization are taking a growing interest as a countermeasure of global worming by carbon dioxide and exhaustion of fossil fuel. The purpose of this study is to investigate the possibility of extracting micro hydropower wasted by a valve in water supply system using micro cross-flow hydraulic turbine. In order to fulfill the functions of controlling flow rate and pressure in substitute for the valve, air and water are supplied into an air suction hole which is installed on the side wall of micro cross-flow hydraulic turbine. The results show that in case of supplying a lot of air into the air suction hole, about 50% of flow rate and relatively high value of loss coefficient are controlled by the turbine. Moreover, including high possibility of applying the micro cross-flow turbine to water supply system, extended application of the turbine to the water discharge system of drainage and irrigation canal.