• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.2
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• pp.10-15
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• 2005

This study was initiated to evaluate the cooling performance of CAC (charged air cooler) and radiator in the engine room of a mini bus. So we had firstly to predict the mass flow rate coming from radiator grille and front bum per opening using computational fluid dynamics (CFD) simulation based on 3D configuration. And simulations were carried out for different cooling module layout and bum per opening hole size on sam e vehicle operating condition. Simulation results show that CAC cooling performance at reverse protecting plate-applying model was much efficient than that of the bum per opening hole size-increasing model in IMTD point of view. Part of the CFD simulation results was com pared to with experimental data. It was confirm ed that the CFD approach using STAR-CD based on pursuing no-com promise solution could provide design engineers with useful design information in the early design stage of vehicle development.

• International Journal of Safety
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• v.3 no.1
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• pp.6-9
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• 2004

This paper deals with the noise evaluation technique of a reciprocating air-compressor and its noise reduction. The reciprocating air-compressors are widely used in the small, medium sized industrial firms, and lots of their employees are affected and irritated by their noise in the workplace. Thus, noise control actions should be taken appropriately by considering the hearing loss due to the occupational noise exposure. Lead-wrapping techniques are employed to identify the contribution of principal noise sources which are generally known as motor, belts, suction/discharge valves, moving pistons, and flow-induced noise caused by edges or discontinuities along the flow path e.g. expansions, contractions, junctions and bends etc .. As a result, main noise sources of the air-compressor can be categorized by the suction/discharge noise, valve noise, and compressed-air tank noise. Based on the investigations, mufflers are designed to reduce both the suction/discharge noise and the compressed-air tank noise. Instead of the conventional valve plate, polyethylene resin is used as a new one for the reduction of valve impact noise. In addition, attempts are made to reduce the valve noise propagation to the cylinder head and the compressor tank by using the insulation casings. As a result of the countermeasure plans, it can be achieved that the noise reduction of the air-compress is up to 10dB.

• International Journal of Automotive Technology
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• v.8 no.5
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• pp.659-666
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• 2007

In the present study, a numerical analysis of the three-dimensional heat transfer and fluid flow for a vehicle cooling system was developed. The flow field of the engine room between the grille and radiator was analyzed. The results show that, as the airflow inlet grille angle $\alpha$ is varied from $15^{\circ}$ to $-15^{\circ}$, the air flow rate compared with $\alpha=0^{\circ}$(horizontal) changes from -11.9% to +5.1%; while the heat flux from the radiator changes from -9.2% to +4.4%. When the airflow inlet bumper angle $\beta$ is varied from $-5^{\circ}$ to $+15^{\circ}$, the heat flux from the radiator compared with $\beta=0^{\circ}$(horizontal) increases up to +4.4%. When the airflow inlet grille angle $\alpha=-15^{\circ}$ and the bumper grill angle $\beta=+15^{\circ}$, the airflow rates and heat flux compared with($\alpha=0^{\circ}$, $\beta=0^{\circ}$) can be increased to +9.5% and +7.5%, respectively. The results indicate that the optimal angles for cooling efficiency are used.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.123-141
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• 1996

In this paper the upwind flux difference splitting Navier-Stokes method has been applied to study the perfect gas and the equilibrium chemically reacting hypersonic flow over an axisymmetric sphere-cone(5°) geometry. The effective gamma(γ), enthalpy to internal energy ratio was used to couple chemistry with the fluid mechanics for equilibrium chemically reacting air. The test case condition was at altitude(30km) and Mach number(15). The equilibrium shock thickness over the blunt body region was much thinner than that of perfect gas shock. The pressure difference between perfect gas and equilibrium gas was about 3 ∼ 5 percent. The heat transfer coefficient were also calculated. The results were compared with VSL results in order to validate the current numerical analysis. The results from current method were compared well VSL results ; however, not well at near nose. The proper boundary condition and grid system will be studied to improve the solution quality.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.4
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• pp.357-364
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• 2011

In this study, ring-shaped acoustic resonators were proposed to be installed in a silencer to increase the acoustic performance of silencer in the low-frequency range. Evaluation of noise reduction performance of acoustic resonator arrays was carried out by measuring the random-incidence absorption coefficient. It was found that the absorption coefficient of resonator array was measured up to 1 at 125 Hz of 1/3-octave band center frequency. Insertion losses of silencers with ring-shaped acoustic resonator arrays were measured based on ISO 7235. The results were shown that the ring-shaped resonator could increase the insertion loss up to 13 dB without flow, whereas 7 dB when flow speed reached 15 m/s. As increasing the flow speed above 15 m/s, the effect of acoustic resonator decreased due to the effect of nonlinear air damping of the resonator. It was also found that the increment of pressure drop by the presence of resonator arrays was about 9 % at flow speed of 25 m/s.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.3
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• pp.165-172
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• 2017

In this study, centrifugal fan blades used to circulate cold air inside a household refrigerator were optimized to achieve high performance and low noise by using the response surface method, which is frequently employed as an optimization algorithm when multiple independent variables affect one dependent variable. The inlet and outlet blade angles, and the inner radius, were selected as the independent variables. First, the fan blades were optimized to achieve the maximum volume flow rate. Based on this result, a prototype fan blade was manufactured using a 3-D printer. The measured P-Q curves confirmed the increased volume flow rate of the proposed fan. Then, the rotation speed of the new fan was decreased to match the P-Q curve of the existing fan. It was found that a noise reduction of 1.7 dBA could be achieved using the new fan at the same volume flow rate.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.307-315
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• 2008

In this study, it is investigated the properties of high strength concrete using mineral admixture, on the purpose of use of meta kaolin for the substitutive materials to silica fume which is so expensive. The plain mixtures are 3 degrees which are ordinary portland cement, blast furnace slag cement and OPC included fly ash 20%, and silica fume and meta kaolin are substituted for the each plain mixtures in the range of 20%. The results of experiment showed as follows. In case of silica fume was only used, the viscosity and slump flow of fresh concrete were much decreased, on the contrary air content increased. But as usage of meta kaolin increased, to being increase the viscosity of fresh concrete, slump flow increased and air content and usage of super-plasticizer were decreased. Accordingly the workabilities of concrete were against tendency between silica fume and meta kaolin. The compressive strength, velocity of ultrasonic pulse and unit weight were increased according to usage of meta kaolin, the properties of hardened concrete were judged that they are affected with air content of fresh concrete, so it is very important to control air content of high strength concrete. Therefore, the use of meta kaolin is prospected to the substitutive material of silica fume, in case of using silica fume and meta kaolin, it is judged that the optimum usage of silica fume and meta kaolin is about 10% respectively, considering workability and strength of concrete.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.5
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• pp.31-36
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• 2010

SAI(Secondary Air Injection) system has been studied widely as one of the promising countermeasure for reducing HC emission at cold start. In this paper, in order to find out the optimal position of SAI, computational thermal fluid analysis on exhaust system adapted SAI system is performed using commercial 3-D CFD code, CFX. The present results showed that SAI position strongly affected the uniformity of air distribution in front of catalyst. And also through the decision process of optimal position of SAI, new index, uniformity of air distribution($U_{\phi}$) is proposed to define it quantitively. Because $U_{\phi}$ is very simple equation and similar with flow uniformity, it is very easy to figure out the physical meaning and to apply it to practices. Finally, we applied the index $U_{\phi}$ to the decision process of the optimal position of SAI, so that we could get the clear comparison results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.528-537
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• 1995

Natural convective flow and heat transfer characteristics in a partially opened enclosure fitted with a horizontal divider are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. A divider is attached perpendicularly to the vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of divider, the opening size, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for air(Pr=0.71). As result, when the opening size is fixed, the intensity of the secondary flow is weaken as the length of divider increases. The maximum heat transfer rate over the upper cold wall occurs at a position bounded on the opening. However, when the length of divider is increased considerably, its maximum occurs at the right wall. The stability and frequency of oscillation are affected by the Rayleigh number and length of divider. The Nusselt number is increased with the increase of the opening size and the increase of Rayleigh number.

• Journal of Animal Environmental Science
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• v.19 no.1
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• pp.47-54
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• 2013

Two types of reactors were set to investigate the change of characteristics of pig slurry by aeration during fertilization period. One system was equipped with air diffuser to supply oxygen to pig slurry for liquid fertilization, but there was no air diffuser in the other system. Air supply to the experimental systems was regulated by air flow meter. The reactors were set up in the laboratory to protect the pig slurry from external condition such as temperature and humidity changes. Maintaining optimal pH range in the experimental reactors is an important factor for liquid fertilization of pig slurry. In this study, pH ranges of aerobic reactor and anoxic reactor was 7.04~7.19 and 7.34~7.81, respectively. The temperature of aerobic reactors was $2{\sim}3^{\circ}C$ higher then indoor temperature. The amount of sludge accumulated at the bottom layer of non-aerated reactors was 4~5 times more than that of aerated reactors.