• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.519-524
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• 2002

An experimental study has been conducted to investigate the effects of surface energy on frost formation. Test samples with two different surfaces are installed in a wind tunnel and exposed to a humid airflow. Dynamic contact angles (DCA) for these surfaces are $23^{\circ}\;and\;88^{\circ}$, respectively. The thickness and the mass of frost layer are measured and used to calculate the frost density while frost formation is visualized simultaneously with their measurements. Results show that frost density increases as time increases at specific test conditions. The air Reynolds number, the airflow humidity and the cold plate temperature are maintained at 12,000, 0.0042 kg/kg and $-21^{\circ}C$, respectively. The surface with a lower DCA shows a higher frost density during two-hour test, but no differences in the frost density have been found after two hours of frost generation. Empirical correlations for thickness, mass and density are assumed to be the functions of the test time and DCA.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.5
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• pp.90-97
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• 2002

The interaction between airflow and liquid phase LfG (Liquefied Petroleum Gas) sprays was investigated in a steady flow system embodied in a wind tunnel to simulate the variety of flow inside intake port of LPG engines with liquid injection system. The spray developments in flowing fields with the mean velocities of 5.4, 21.5 and 42.4m/s were identified by spray visualization techniques such as Mie scattering and shadowgraph. The microscopic visualization using a telescopic lens system was performed to investigate the shape and size of liquid droplets in the spray. PDA measurement was used to get 1-dimensional velocity and diameter of liquid droplets. The fast co-flows make the spray field be compact and be lead upward to the injection direction. SMD of the spray was smaller at the fast flowing field. Spray width got bigger and SMD of the spray was smaller with higher injection pressure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.2
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• pp.689-694
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• 2018

Recently, fuel consumption efficiency has become the most important issue in the vehicle development process due to the problem of environmental pollution. The air flow patterns of the vehicle body line and rear part are the most important elements affecting the fuel consumption efficiency. Especially, the airflow pattern of the vehicle rear part is the most important design factor to be considered in rear spoiler design. In this paper, the control factors affecting the airflow of the rear spoiler are determined, the airflow sensitivity of these control factors are tested and, then, the optimized control factors to reduce the airflow drag force are proposed. The model of optimized control factors is tested and the values of the optimized control factors are changed by analyzing the S/N ratio and mean value. Finally, the new modified model incorporating the optimized control factors is tested in an air flow tunnel and its ability to decrease the air drag and reduce the cost is verified.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2010.04a
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• pp.245-247
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• 2010

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.435-438
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• 2002

In this study, a new passive aerodynamic control method is proposed. Control plate which is oscillated by TMD-like mechanism makes flutter stabilizing airflow. Effectiveness of proposed model is verified by experimental and analytical study. In addition, various parameters of the proposed system are investigated. Applicability to long span bridge is also examined. According to the research results, proposed model is very effective in suppressing flutter, and it also shows remarkable robustness.

• Fire Science and Engineering
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• v.30 no.2
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• pp.68-74
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• 2016

In semi-transverse ventilation system applied for road tunnel, adjustment of the port opening ratio is an essential part for uniform airflow rate per unit length over the entire tunnel. However, it has not been considered decently throughout the design process and operating of the tunnel. Therefore, in this study, we developed a program for the calculation of the opening size ratio of supply or exhaust port in transverse ventilation system and carried out the research to present a management plan for the port. In supply duct system, the opening size of the port had a tendency to increase and then decrease later when it gradually becomes closer toward the bulkhead at the beginning of the duct the minimum opening degree is to appeared as 56%. In the exhaust system, port size is the smallest at the beginning of duct as 15%, has shown a tendency to increase towards the bulk head. As results of estimating the air flow rate for 300 m intervals, the exhaust flow rate in the center of tunnel appeared to be extremely low as 8.1% and 12.5% when port size is constant and is adjusted supply type. Thus, even if the normal ventilation efficiency is declines, yet it is highly recommend adjusting the port size in order to obtain a uniform flow rate at fire accidents.

• Journal of the Korean Society for Railway
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• v.9 no.5 s.36
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• pp.550-554
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• 2006

In the early stage of operation of KTX, passengers complained of the excessive cabin noise as the passes the tunnel. The noise is caused partly by wheel-rail contact and partly by airflow around the carbody. In this study, to reduce the cabin noise, the effect of the mud-flaps located between the cars is investigated. A series of tests was conducted to clarify the influences of the type and length of mud-flap, and train speed on the cabin noise. The optimum length of mud-flap was found. The shedding vortices around the mud-flap is thought to be the cause of the aerodynamic noise. Strouhal number and the resonant shedding frequency around the mud-flap correlated well with the cabin noise level.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.7
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• pp.337-343
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• 2015

This paper investigates the ventilation characteristics in a two-dimensional underground network junction composed of four main lines interconnected by eight ramps. Simple one-dimensional models cannot be applied to network junctions since there are interferences of traffic piston effects in the main lines and at the ramps. A numerical algorithm was developed to analyze the pressure and airflow distributions iteratively. The Darcy-Weisbach equation was used to calculate the piston effects by traffic flows, and a Hardy Cross iteration was conducted for network analysis at the interconnected junction. The results show interesting ventilation characteristics and CO concentration distributions depending on system parameters such as vehicle speed, tunnel diameter, and other junction configurations.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.637-644
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• 2016

This paper is a follow-up to previous papers entitled, "Development of Tunnel-Environment Monitoring System and Its Installation" I [1] and II [2]. The target tunnel of these studies is the Solan Tunnel, which is a loop-type, single-track, 16.7-km-long tunnel located in mountainous terrain and passing through the Baekdudaegan mountain range. It is an ordinary railway tunnel designed for both freight and passenger trains. We analyzed the environmental conditions of the tunnel using temperature and humidity data recorded over approximately one year. The data were recorded using the Tunnel Rough Environment Measuring System (TREMS), which measures environmental data in subway and high-speed train tunnels and is installed in three locations inside the tunnel. Previous studies analyzed environmental conditions inside tunnels located in or near a city, whereas the tunnel in this study is located in a mountainous area. The tunnel conditions were compared with those measured outside the tunnel for each month. Hourly changes during summer and winter periods were also analyzed, and the environmental conditions at different locations inside the tunnel were compared. The results are widely applicable in studies on the thermal environment and air quality of tunnels, as well as for computer analysis of tunnel airflow such as tunnel ventilation and fire simulations.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.226-235
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• 2009

Force induced by the natural ventilation in tunnel is likely to generate adverse influences on the airflow during the normal operation and create even more unfavorable circumstances during the tunnel fire. The influence of the natural ventilation is required to take into account in designing and operating the ventilation as well as safety systems. The magnitude of natural ventilation force depends on a variety of factors associated with the topographical, meteorological and physical features of tunnel. Unfortunately, at this moment those are difficult to quantify and none of the countries has suggested its estimation method in the design guideline. This study aims at quantifying the natural ventilation force at a local highway tunnel by three different methods. The first method employes direct measurement of the pressure at portals, while the second applies a stepwise approach to eliminate the piston effect ahead of deriving the natural ventilation force and the third method uses the concept of barometric barrier.