• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.5
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• pp.627-633
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• 2001

Characteristics of a diesel spray impingement with the variation of ambient temperature, wall temperature and ambient pressure were investigated through shadowgraphy method by using high speed camera. The radial penetration of spray was increased with ambient temperature and wall temperature. It is resulted from the decrease of ambient gas density caused by the increase of temperature. The height of spray was also increased with ambient temperature and wall temperature, because the height of stagnate region is noticeably increased, although height of wall jet vortex is decreased. At the same ambient pressure, the area ratio of impinging spray of room temperature environment to high temperature environment was increased, as the temperature difference between room temperature and high temperature increases. And the increment of area ratio was higher at low ambient pressure than high ambient pressure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.7 s.238
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• pp.828-836
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• 2005

Impingement/effusion cooling technique is used for combustor liner or turbine parts cooling in gas turbine engine. In the impingement/effusion cooling system, the crossflow generated in the cooling channel induces an adverse effect on the cooling performance, which consequently affects the durability of the cooling system. In the present study, to reduce the adverse effect of the crossflow and improve the cooling performance, circular pin fins are installed in impingement/effusion cooling system and the heat transfer characteristics are investigated. The pin fins are installed between two perforated plates and the crossflow passes between these two plates. A blowing ratio is changed from 0.5 to 1.5 for the fixed jet Reynolds number of 10,000 and five circular pin fin arrangements are considered in this study. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The results show that local distributions of heat/mass transfer coefficient are changed due to the installation of pin fins. Due to the generation of vortex and wake by the pin fin, locally low heat/mass transfer regions are reduced. Moreover, the pin fin prevents the wall jet from being swept away, resulting in the increase of heat/mass transfer. When the pin fin is installed in front of the impinging let, the blockage effect on the crossflow enhances the heat/mass transfer. However, the pin fin installed just behind the impinging jet blocks up the wall jet, decreasing the heat/mass transfer. As the blowing ratio increases, the pin fins lead to the higher Sh value compared to the case without pin fins, inducing $16\%{\~}22\%$ enhancement of overall Sh value at high blowing ratio of M=1.5.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.9
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• pp.2991-3006
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• 1996

An experimental study of jet flow and heat transfer has been carried out for the jet impingement cooling on a semi-circular concave surface. For the jet impingement on the concave surface, three different regions-free jet region, stagnation region, and wall jet flow region-exist, and the distributions of mean velocity and fluctuating velocity for each region have been measured by Laser Doppler Velocimeter. Of particular interests are the effects of jet Reynolds number, the distance between the nozzle exit and cooling surface apex, and the distance from the stagnation point in the circumferential direction. The resulting characteristics of heat transfer at the stagnation point and the variation of heat transfer along the circumferential direction including the existence of secondary peak have been explained in conjunction with measured impinge jet flow.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.25-31
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• 2010

Interface tracking of two phase is significant to analyze multi-phase phenomena. The VOF(Volume of Fluid) and level set are well known interface tracking method. However, they have limitations to solve compressible flow and incompressible flow at the same time. CIP(Cubic Interpolate Propagation) method is appropriate for considering compressible and incompressible flow at once by solving the governing equation which is divided up into advection and non-advection term. In this article, we analyze the droplet impingement according to various We number using improved CIP method which treats nonlinear term once more comparison with original CIP method. Furthermore, we compare spread radius after droplet impingement on the wall with the experimental data and original CIP method. The result using improved CIP method shows the better result of the experiments, comparison with result of original CIP method, and it reduces the mass conservation error which is generated in the numerical analysis comparison with original CIP method.

• Journal of ILASS-Korea
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• v.18 no.1
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• pp.9-15
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• 2013

Wall thinning of pipeline in power plants occurs mainly by flow acceleration corrosion (FAC), cavitation erosion (C/E), liquid droplet impingement erosion (LDIE). Wall thinning by FAC and C/E has been well investigated; however, LDIE in plant industries has rarely been studied due to the experimental difficulty of setting up a long injection of highly-pressurized air. In this study, we designed a long-term experimental system for LDIE and investigate the behavior of LDIE for three kinds of materials (A106B, SS400, A6061). The main control parameter was the air-water ratio (${\alpha}$), which was defined as the volumetric ratio of water to air (0.79, 1.00, 1.72). In order to clearly understand LDIE, the spraying velocity (${\nu}$) of liquid droplets was controled larger then 160 m/s and the experiments were performed for 15 days. Therefore, this research focuses relation between erosion rate and air-water ratio on the various pipe-flow materials. NPP(nuclear power plant)'s LDIE prediction theory and management technique were drawn from the obtained data.

• Corrosion Science and Technology
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• v.12 no.4
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• pp.179-184
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• 2013

Pipe wall thinning caused by erosion and corrosion can adversely affect the operation of aged nuclear power plants. Some injured workers owing to pipe rupture has been reported and power reduction caused by unexpected pipe damage has been occurred consistently. Therefore, it is important to develop erosion-corrosion damage prediction model and investigate its mechanisms. Especially, liquid droplet impingement erosion(LDIE) is regarded as the main issue of pipe wall thinning management. To investigate LDIE mechanism with corrosion environment, we developed erosion-corrosion damage simulation apparatus and its capability has been verified through the preliminary damage experiment of 6061-Al alloy. The apparatus design has been based on ASTM standard test method, G73-10, that use high-speed rotator and enable to simulate water hammering and droplet impingement. The preliminary test results showed mass loss of 3.2% in conditions of peripheral speed of 110m/s, droplet size of 1mm-diameter, and accumulated time of 3 hours. In this study, the apparatus design revealed feasibility of LDIE damage simulation and provided possibility of accelerated erosion-corrosion damage test by controlling water chemistry.

• Archives of Plastic Surgery
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• v.38 no.6
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• pp.879-882
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• 2011

Purpose: Superior orbital fissure syndrome is a rare neurological complex. Superior orbital fissure syndrome may result from a variety of inflammatory, infectious, neoplastic, iatrogenic, traumatic, vascular cause. The author report a patient who suffered from superior orbital fissure syndrome after inferior orbital wall reduction. Methods: A 26-year-old female suffered from inferior orbital wall fracture with inferior gaze limitation and orbital soft tissue herniation. On posttrauma 10 day, inferior orbital wall was reduced using endoscope and porous polyethylene ($Medpor^{(R)}$) was inserted. On immediate postoperation, she reported that extraocular movement was limited in almost any directions. She underwent exploration surgery to release the presence of extraocular muscle impingement. But, there was no observation of extraocular muscle impingement. On postoperative one day, high-dose steroid therapy was started to release superior orbital fissure syndrome which was defined in postoperative computed tomography. Results: After one month of high-dose steroid therapy, extraocular movement limitations improved progressively in all directions. In four months, extraocular movement recovered completely. Conclusion: Superior orbital fissure syndrome may occur after surgical procedure of orbital wall reduction. Prompt diagnosis and treatment with mega-dose corticosteroid is an effective option for avoiding disaster from compressive syndrome.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.5
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• pp.329-339
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• 2017

Impingement jets have been applied in a wide variety of fields as they provide significantly high heat transfer on the impingement-jet stagnation zone. However, the crossflow in an impingement chamber developed by spent wall jets can disrupt and deflect the downstream jets in the array, leading to a decrease in the cooling performance of an array of impingement jets. A numerical analysis is made of the fluid flow and heat transfer characteristics in a corrugated structure that traps the spent air in the corrugations between impingement jets and reduces crossflow effects on downstream jets. All computations are performed by considering a three-dimensional, steady, and incompressible flow by using the ANSYS-CFX 15.0 code. The effects of the configuration parameters of the corrugated structure on crossflow reduction of the array of impingement jets are presented and discussed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.4
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• pp.255-267
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• 2020

Under SLD conditions, due to the large size of droplets, physical phenomena such as wall-droplet interaction and deformation have a significant effect on the icing process. Accordingly, many studies have been conducted in order to computationally simulate SLD effects. As one of the efforts, post-processing method have been proposed to describe wall-droplet interaction effect, which modified collection efficiency using Wright model. However, since the model doesn't properly consider the wall condition, it still overestimated collection efficiency and impingement limit. To solve this problem, impingement areas were divided into 3 different regions, and the post-processing method was introduced with the new wall-droplet interaction model developed based on Bai and Gosman rebound model. In order to consider the effect of deformation, the most suitable model was selected by comparing the deformation models used in the various icing codes. As a result, the modified post-processing method showed improved accuracy in predicting the impingement limits and collection efficiency by further estimating mass flux loss due to rebound, and it was observed that the result was the closest to the experimental data when the deformation effect was included by using Wiegand model.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.281-285
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• 2005

Viscous solutions of supersonic jet impinging on a flat wall in a confined plenum are simulated using three-dimensional Navier-Stokes solver. A confined plenum was designed for simulating the missile launch and analyzing the behavior of the exhaust plume, which were accompanied by complex flow interactions with shock and boundary layer. Concerns of this paper are to show accurate simulation of internal flow in confined plenum and to demonstrate the jet flow structure when the jet interacts with a small opening on the side. Objectives of this numerical simulation are to understand the effect of changing the plume exit area of the plenum. Pressure and temperature rise at certain position in the plenum are traced and compared with test data.