• The KSFM Journal of Fluid Machinery
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• v.15 no.2
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• pp.57-62
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• 2012

The constant air volume flow fan can maintain constant flow rate to the wide range of exit pressure. Therefore, the use of this fan is increasing recently for ventilation of high building. Brushless DC motor is adopted to this fan because that has advantages of compactness and performance. But this type of motor protrude from impeller hub side to fan inlet. The Impeller inlet flow is influenced by size of this obstacle called hub. In this paper, the influence of hub shape on the fan performance characteristics are experimentally and numerically analyzed. CFX 12.0 is used to perform the fan internal flow analysis and numerical results are compared with the experiments. Depending on hub shape, internal loss is generated and the performance and efficiency are reduced. The best performance is occurred around $h/b_1$ = 0.25. The results of this study will be contribute to initial design of constant air volume flow fan development.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.285-293
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• 1997

Numerical calculations has been performed for the flow and heat transfer to a circular cylinder from a hot circular impinging air jet. The characteristics of the flow and heat transfer are investigated and compared with the two-dimensional flow. The present study lays emphasis on the investigation on the flow and heat transfer of the three-dimensionality. The effects of the buoyancy force and the size of jet are also studied. The noticeable difference between the three and the two-dimensional cases is that there is axial flow of low temperature into the center-plane of the cylinder from the outside in the recirculation region. Local Nusselt number over the cylinder surface has higher value for the large jet as compared with that of the small jet since the energy loss of hot jet to the ambient air decreases with increase of the jet size. As buoyancy force increases the flow accelerates so that the period of cooling by the ambient air is reduced, which results in higher local Nusselt number over the surface.

• Journal of the Korean Society of Visualization
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• v.7 no.1
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• pp.3-8
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• 2009

Most vehicles have a heating, ventilating and air conditioning (HVAC) device to control the thermal condition and to make comfortable environment in the passenger compartment. The improvement of ventilation flow inside the passenger compartment is crucial for providing comfortable environment. For this, better understanding on the variation of flow characteristics of ventilation air inside the passenger compartment with respect to various ventilation modes is strongly required. Most previous studies on the ventilation flow in a car cabin were carried out using computational fluid dynamics (CFD) analysis or scale-down water-model experiments. In this study, whole ventilation flow discharged from the air vent of a real passenger car was measured using a special PIV (particle image velocimetry) system for large-size FOV (field of view). Under real recirculation ventilation condition, the spatial distributions of stream-wise turbulence intensity and mean velocity were measured in the vortical panel-duct center plane under the panel ventilation mode. These experimental data would be useful for understanding the detailed flow structure of real ventilation flow and validating numerical predictions.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.6
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• pp.825-832
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• 2010

The objective of this study is to investigate flow behaviors of polluted air in order to prevent the impact of disaster in a tunnel. This paper presents the experimental results qualitatively in terms of flow characteristics in two kinds of rectangular tunnel models in which each distance from the centerline above the inlet vent to the exhaust vent is 0 and 60 mm, respectively. The olive oil is used as the tracer particles. The flow is tested at the flow rate of $14.16{\times}10^{-4}\;m^3/s$ and the inlet vent velocity of 1.1 m/s with the kinematic viscosity of air. The aspect ratio of the model test section is 10. The average velocity vectors, streamlines, and vorticity distributions are measured and analyzed by the Flow Manager in a particle image velocimetry(PIV) system. The PIV technology gives three different velocity distributions according to observational points of view for understanding the polluted air flow characteristics. The maximum value of mean velocity generally occurs in the inlet and outlet vent regions in the tunnel models.

• The KSFM Journal of Fluid Machinery
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• v.7 no.6 s.27
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• pp.28-37
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• 2004

An experimental study is conducted to investigate flow characteristics on a small axial-type turbine which is applied as the rotating part of air tools. It operates in a partial admission due to consumption restriction of the high pressure air. In this operating condition, it is necessary to understand flow characteristics for obtaining the high specific output power. Tested turbine consists of two stages and the mean radius of flow passage is less than 10mm. A 6 bar pressure air is used to operate the turbine. The experimental results show that flow angles depend on the measuring location along the circumferential direction, but its discrepancy is alleviated along the axial direction. Absolute flow velocities show three times difference according to the measuring location at the exit of the first rotor due to the partial admission, but they show similar value at the exit of the second rotor by the velocity diffusion. From the measured flow angles and velocities, a ratio of output power obtained by the first and second rotor is estimated. It shows that the output power obtained by the second rotor is about $11\%$ to that by the first rotor at 60,000 RPM. It is effective therefore to improve the first rotor for increasing the turbine output power.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2713-2717
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• 2008

Whole flow fields of a room air conditioner (RAC) have been visualized by a Particle Image Velocimetry (PIV) technique to analyze the flow structure with various inlet and outlet angles, and to control an eccentric vortex which affects an efficiency and noise of the RAC. A test model with 5 stages of a cross flow fan has been manufactured and a transparent acryl has been installed at the side of the test model for the PIV experiment. The inlet and outlet flows and the flow inside the cross flow fan have been analyzed by varying the inlet grill angles and outlet blade angles. The movement of the eccentric vortex has been investigated experimentally by developing the measurement technique for the inner flow field of the cross flow fan. From the visualization of the inner flows, the origins of the noise inside the RAC and the condensation points around the outlet parts of the cold air have been observed and the solution of the problems can be proposed in this study.

• Korean Journal of Acupuncture
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• v.27 no.4
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• pp.35-47
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• 2010

Objectives : To characterize the thermal properties of traditional warm needle and new warm needle with various air flows as an important environmental factor and to suggest the necessity of maintaining suitable environment of clinics to maximize their efficacy. Methods : We measured the temperature characteristics of traditional moxa warm needle and new moxa charcoal warm needle by applying an automatic temperature acquisition system with thermocouples while external various air flows were supplied. Temperatures of two positions at the needle body were measured while a moxa cone burned. Typical temperature characteristics like peak temperature, duration, curve shape and the efficiency of the heat stimuli by heat amount analysis were executed. Results : Both warm needles showed similar temperature curve with an increase in the air flow. Peak temperature and duration of effective heat decreased with the air flow, as shown in indirect moxibustion on garlic. The temperature change pattern by the air flow became more apparent when the total combustion heat was compared with the effective heat. The values from two positions on the needle body were significantly different, showing a distance dependency from the heat source of warm needle acupuncture. Conclusions : Thermal properties of warm needle acupuncture was observed variously with surrounding air flow of 0.0 - 0.7 m/s. It emphasized the importance of environmental control as well as the warm needle itself such as heat source and needle. The latter has already been known to deliver designated heat to subjects. It also indicated the importance of education and skill of the practitioners of warm needle acupuncture.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.3
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• pp.268-276
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• 2005

The aim of this paper is to suggest one efficient method for the various requirements of performance during the process designing and producing an impeller. The study considers that the revisions of a pitch angle of an impeller at an axial turbo fan affect an air flow rates and a static pressure rise. The axial turbo fan specified with the 250 Pa maximum static pressure and 1300 CMH fan air flow rates was tested and analyzed by CFD. The Numerical results show that the air flow rates are calculated to 1,175 CMH, 1,223 CMH, 1,270 CMH, 1,340 CMH and 800 CMH in cases that the pitch angles are $44^{\circ},\;49^{\circ},\;54^{\circ},\;59^{\circ},\;and\;64^{\circ}$ respectively. Also the static pressure rises are shown to 108 Pa, 122Pa, 141 Pa, 188 Pa and 63 Pa at the same cases. The air flow rate is increased linearly according to the changes of the pitch angle from $44^{\circ}\;to\;59^{\circ}$ and the maximum air flow rate passing the impeller is increased to $13\%$ over at the case of $59^{\circ}$ pitch angle compared with the reference case of $54^{\circ}$ pitch angle. The static pressure rise is increased linearly according to the changes of the pitch angle from $44^{\circ}\;to\;54^{\circ}$, too. The static pressure rise at the $59^{\circ}$ pitch angle is increased to $33\%$ over compared with the $54^{\circ}$ pitch angle. The result shows that the revisions of pitch angle make the static pressure rise increase widely. However the air flow rates and the static pressure rise at the $64^{\circ}$ pitch angle are suddenly decreased because of over-changed pitch angle.

• Transactions of the KSME C: Technology and Education
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• v.2 no.2
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• pp.105-111
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• 2014

Generally the lower part of the Earth's atmosphere, which is 20km above the ground, is called "air." The composition of this area is almost consistent consisting of nitrogen, oxygen, and other gases. Air density refers to the mass per unit volume of earth atmosphere. Though air is made of the mixed gases in a constant composition, the water vapor is one of the very changeable components. The density of moist air is lower than the dry one at the same temperature and pressure. As the density varies according to the pressure and temperature, this paper attempts to explore the main factors in the air quantity calculation by examining first the density calculation process according to the air property, and second the relation between the actual and standard air flow.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.4
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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.