• Journal of Korea Water Resources Association
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• v.36 no.6
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• pp.971-984
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• 2003

This paper presents the hydraulic analysis of the air entrainment by the weir types. For the weir types, the stepped weir, the labyrinth weir and the gate underflow weir were selected, and the oxygen transfer efficiency was estimated by the site investigation and the hydraulic model tests. The most effective type for the oxygen transfer was stepped weir The more steps the stepped weir had, the higher efficiency it revealed. Oxygen transfer was proportional to the flow velocity, the Froude number, and the flow discharge in order. Hydraulic model tests showed that a nappe flow occurred at small flow rates. The concurrent condition of a nappe flow and a skimming flow occurred as flow rate increases, nappe flow at the upper part and skimming flow at the lower part. In the region of nappe flow, air inception occurred from the step edges due to flow separation, and air entrainment was made through a free-falling nappe, an air pocket, a nappe impact and a subsequent hydraulic jump. In the region of skimming flow, air entrainment occurred by the variation of water surface over the steps, but it was relatively small compared with nappe flow.

• Journal of Biosystems Engineering
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• v.15 no.1
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• pp.14-22
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• 1990

For efficient use of solar energy in plastic greenhouse, thermal storage system was developed. The system was constructed with the counter-flow type air-water heat exchanger using a thin polyethylene film as a medium of heat exchange parts. Experiments were carried out to investigate the heat exchange rate, optimum water flow rate, overall heat transfer coefficient, and the effectiveness of the counter-flow type air-water heat exchanger with polyethylene film bags. Mathematical model to predict air temperature leaving heat exchanger was developed. The results obtained in the present study are summarized as follows. 1. Heat exchange rate in the counter-flow type air-water heat exchanger with polyethylene film bags was compared to that of polyethylene film. Heat exchange rate was almost identical at air velocity of 0.5m/s on polyethylene film surface. But, heat exchange rate of heat exchanger with polyethylene film bag was $32{\sim}55KJ/m^2$ hr higher than that of polyethylene film at air velocity of 1.0m/s. 2. Considering the formation of uniform water film and the sufficient heat exchange rate of polyethylene film bags, optimum water flow rate in polyethylene film bags was $3.0{\sim}6.0{\ell}/m^2$ min. 3. The overall heat transfer coefficient of polyethylene film bags was found to be $35.0{\sim}130.0KJ/m^2\;hr\;^{\circ}C$ corresponding to the air velocity ranging 0.5 to 4.0 m/s on polyethylene film surface. And the overall heat transfer coefficient showed almost linearly increasing tendency to the variation of air velocity. 4. Mathematical model to predict air temperature leaving the heat exchanger was developed, resulting in a good agreement between the experimental and predicted values. But, the experimental results were a little lower than predicted. 5. Effectiveness of heat exchanger for the experiment was found to be 0.40~0.81 corresponding to the number of transfer units due to the variation of air velocity ranging 0.6 to 1.7 m/s.

• Journal of ILASS-Korea
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• v.20 no.2
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• pp.76-81
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• 2015

Swirl flow has an impact on the stabilization of the flame by the recirculation flow, improvement of the combustion efficiency. The swirl flow in the gun type burner is created by the spinner which is inside the airtube that guide the combustion air. Burner has generally the combustion device composed electronic spark plug, injection nozzle, combustion device adaptor, and spinner. These inner components change the air flow behavior passing through airtube. So, this study analyzed exhaust flow characteristics of the gun type burner according to the ratio of airtube diameter. Turbulence characteristics by the spinner was mean velocity, turbulence intensity, kinetic energy, shear stress and flattness factor of the air flow of axial direction and tangential direction from the exit of the airtube.

• Journal of computational fluids engineering
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• v.11 no.3 s.34
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• pp.52-58
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• 2006

A numerical investigation is made of air flow in a spinner equipment used for cleanning and drying flat display panels. A unique feature of the spinner under question is the placement of a torus plate cover over the rotating plate. The turbulent flow is driven by rotation of a large disk and suction by the exhaust system connected to vacuum chamber. The flow is modelled as an axisymmetric two-dimensional flow and computation is conducted by using the FLUENT package with a version of k-$\varepsilon$ turbulence model. The required capacity of the exhaust system is assessed numerically. The usefulness of the cover in controlling air flow circulation is examined. A computational trouble shooting is attempted to resolve the problem of panel rising which occurred in real experiment.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.7
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• pp.24-31
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• 1999

The MPI engine becomes increasingly popular because it meets two requirements of stringent pollutant emission and the lower fuel consumption. Even though supplies the same amount of fuel to each cylinder , it is hard to precisely control the air-duel ration due to the different amount of air flowing into each cylinder. The uniformity of air-fuel ration in each cylinder is considerably affected by the plenum chamber configuration . This study is focused on experimentally analyzing the flow characteristics within the plenum chamber In the present experiment , steady and valve dynamic state flow tests are performed and the flow field inside the plenum chamber is visualized and measured by utilizing a laser sheet visualization technique and a PTV method. These measured results indicate that the flow structure in the plenum chamber is highly influenced by the plenum chamber configurations, suction flow rates, crank speeds and so on.

• Plant Journal
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• v.6 no.2
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• pp.62-69
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• 2010

The stability of coal pulverizer in the 800 MW coal-fired plants is vital to maintain their performance. Thus, this study analyzed the uneven abrasion of the deflector and coal spillage due to the air velocity maldistribution in the vane wheel of a bowl-type pulverizer as it is a possible cause for problems of facility using pulverized coal. In addition, air flow in the underbowl of a bowl-type pulverizer was studied to check air velocity maldistribution in the vane wheel using numerical method. In an attempt to correct the maldistribution of air velocity, air flow of the modified duct vane was studied as enlarging the length of the duct vanes installed at the air inlet duct of the pulverizer and increasing the angle of inclination. It was found that modified duct vane make the velocity distribution at the vane wheel uniform. formed by the duct vanes installed at the air inlet duct of the pulverizer and swirling flow is the major factor in making the velocity distribution of vane wheel exit uniform. This can prevent the uneven abrasion of the deflector, which is one of the components inside the pulverizer and coal spillage.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.9
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• pp.687-697
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• 2006

The air and water flow distribution are experimentally studied for a heat exchanger composed of round headers and 10 flat tubes. The effects of tube protrusion depth as well as mass flux, and quality are investigated, and the results are compared with the previous 30 channel results. The flow at the header inlet is annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted geometry, significant portion of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, different from the downward configuration, significant portion of the water flows through the rear part of the header. The effect of the protrusion depth is the same as that of the downward flow. As the protrusion depth increases, more water is forced to the rear part of the header. However, the effect of mass flux or quality is opposite to the downward flow case. As the mass flux or quality increases, more water flows through the frontal part of the header. Compared with the previous thirty channel configuration, the present ten channel configuration yields better flow distribution. Possible explanation is provided from the flow visualization results.

• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.17-20
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• 2006

Passenger safety is fundamental factor in automobile. Among much equipment for passenger safety, the air bag system is the most fundamental and effective device. Beside of the front air bag system which installed on most of all automobiles, a curtain-type air bag is increasingly adapted in deluxe cars fur protecting passengers from the danger of side clash. Curtain type airbag system consists of inflator housing, fill hose, curtain airbag. Inflator housing is a main part of the curtain-type air bag system for supplying high-pressure gases to deploy the air bag-curtain. Fill hose is a passageway to carry the gases from inflator housing to each part of curtain airbag. Therefore, it is very important to design the vent holes of fill hose for good performance of airbag deployment. But, the flow information from vent holes of fill hose is very limited. In this study, we measured instantaneous velocity fields of a high-speed flow ejecting from the vent holes of fill hose using a dynamic PIV system. From the velocity Held data measured at a high frame-rate, we evaluated the variation of the mass flow rate with time. From the instantaneous velocity fields of flow ejecting from the vent holes in the initial stage, we can see a flow pattern of wavy motion and fluctuation. The flow ejecting from the vent holes was found to have very high velocity fluctuations and the maximum velocity was about 480m/s at 4-vent hole region. From the mass flow rate with time, the accumulated flow of 4-vent hole has occupied about 70% of total flow rate.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.404-408
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• 2009

The liquid desiccant air-conditioning system has been proposed as an alternative to the conventional vapor compression cooling systems to control air humidity. The complete system of liquid desiccant air-conditioning system is consisted two main components those are humidifier (regeneration) and dehumidifier. Humidifier part is connected to the load when summer season which is the air condition is hot and humid have to be turned into comfort condition on human. This paper purpose is performances study of air flow rate effect on a structured packed tower on cooling and dehumidifier system using liquid lithium chloride as the desiccant. Experimental apparatus used in this present study is consisted of three components those are load chamber, packed tower and chiller. Load chamber’s volume is $40m^3$, and packed tower dimension is cubic with length 0.4m occupied with packed column. Totally, 15 experimental has done using 5 times repeat on each variable of air velocity that varying on 2m/s, 3m/s and 4m/s with other conditions are controlled. Air inlet initial temperature and relative humidity are set respectively on $30^{\circ}C$ and 52%, desiccant flow rate is 0.63 kg/s, desiccant temperature is $10^{\circ}C$ and desiccant concentration is 0.4. The result of this study shows that averagely, the moisture removal rate and the heat transfer rate are influenced by the air velocity. Higher air velocity will increase the heat transfer and decreasing the moisture removal rate. At adiabatic condition the air velocity of 2 m/s respectively is having the higher moisture removal rate acceleration then the air velocity of 3m/s and 4 m/s until the steady state condition.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.3
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• pp.552-562
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• 2001

Measurement of average of heat transfer and friction coefficients were obtained with air flowing through electrically heated ducts having square, rectangular(aspect ration, 5), and triangular cross section for range of surface temperature from $540^{\circ}$to $1780^{\circ}$ R and Reynolds number from 1000 to 330,000. The results indicates that the effect of heat flux on correlations of the average heat transfer and friction coefficients is similar to that obtained for circular tubes in previous investigation and was nearly eliminated by evaluating the physical properties and density of the air a film temperature halfway between the average surface and fluid bulk temperatures, With the Nusselt and Reynolds numbers on the hydraulic diameter of the ducts, the data for the noncircular ducts could be represented by the same equations obtained in the previous investigation for circular tubes. Correlation of the average difference between the surface corner and midwall temperatures for the square duct was in agreement with predicted values from a previous analysis. However, for the rectangular and triangular ducts, the measured corner temperature was greater by approximately 20 and 35 percent, respectively, than the values predicted by analysis.