• Asian-Australasian Journal of Animal Sciences
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• 제12권8호
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• pp.1310-1315
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• 1999

Air quality in confinement pig houses is important to production and health. Mechanical ventilation and confinement is known to be the most practical tool for maintaining adequate air quality in pig houses through extensive researches since Millier (1950) invented the 'slotted inlet' ventilation system. A variety of mechanical ventilation systems have been applied to confined nursery pig houses in Korea without scientific verification of their ventilation effectiveness. Ventilation systems with three feasible combinations (NA, NB, and NC) of inlets and outlets in a confined nursery pig house were tested to evaluate their ventilation efficiency, of which the one with the performance was supposed to be taken as a standard ventilation system for nursery pig houses in Korea. Field data of air velocity and temperature fields, and ammonia concentration with three ventilation systems were taken and compared to determine the best system. The air velocity and temperature fields predicted by the PHOENICS computer program were also validated against the available experimental data to investigate the feasibility of computer simulation of air and temperature distribution with an acceptable accuracy in a confined house. NC system with duct-induced in-coming air, performed best among the three different ventilation systems, which created higher velocity field and evener distribution ($2.5m/s{\pm}0.3m/s$) over the space with a Reynolds number of $10^4$. The experimental data obtained also fitted well with the simulated values using the modified PHOENICS, which suggested a viable tool for the prediction of air and temperature field with given calculation geometries.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.611-617
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• 2008

Nowadays Plate Heat Exchanger (PHE) is widely used in different industries such as chemical, food and pharmaceutical process and refrigeration due to the efficient heat transfer performance, extreme compact design and efficient use of the construction material. In present study, discussed main conception of plate heat exchanger and applied in vacuum. PHE and aimed apply in the fresh water generator which installed in ship to desalinate seawater to fresh water use heat from engines. The experiment is proceeded to investigate the heat transfer between cold and hot fluid stream at different flow rate and supply temperature of hot fluid. Generated fresh water as outcome of the system. PHE is an important part of a condensing or evaporating system. One of common assumptions in basic heat exchanger design theory is that fluid is to be distributed uniformly at the inlet of each fluid side and throughout the core. However, in practice, flow mal-distribution is more common and can significantly reduce the heat exchanger performance. The flow and heat transfer are simulated by the k-$\varepsilon$ standard turbulence model. Moreover, the simulation contacted flow maldistribution in a PHE with 6 channels.

• 한국입자에어로졸학회지
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• 제9권2호
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• pp.79-87
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• 2013

In this study, the characteristics of turbulent flow and collection efficiency for an one-stage electrostatic precipitator(ESP) with slit type collecting electrode for urban railway underground tunnels were obtained using computational fluid dynamics(CFD) commercial code FLUENT 6.3 and lab-scale experiments. The electrostatic precipitator was operated under high gas velocity(3~12m/s). Five different designs of collecting electrode, flat plate-type and a slit-type of 3mm, 5mm, 7mm and 10mm slit width and four various gas velocity(3, 6, 9, and 12m/s) were used and applied. A standard k-${\varepsilon}$ model in CFD commercial code FLUENT 6.3 was used for flow simulation. The flow simulation results showed that the turbulent intensity of flat plate-type was higher than slit-type under all gas velocity conditions and also the turbulent intensity of flat plate-type was increased continuously, but in case of slit-type was maintained at constant range. And, the turbulent intensity was decreased according to increasing of slit width. The experimental results showed that the collection efficiency of slit-type was higher than flat plate-type under all gas velocity conditions. And, over 6m/s gas velocity condition, the collection efficiency of 5mm and 7mm was highest, when compared to 3mm and 10mm.

• 한국안전학회지
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• 제15권1호
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• pp.72-79
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• 2000

In recent, occupational diseases in harmful working places become a social issue. It is the well-known fact that a respiration in polluted working places exert a serious effect on health of workers. Accordingly, the cutting off contaminants air originally is the best way to improve working environments. In these cases, ventilation systems should be essentially installed to dilute or exhaust the contaminated indoor air. In this study, we investigated the characteristics of ventilation system of the noxious gas in working indoor places with natural ventilation by using COMET. The numerical simulations were carried out the natural ventilation with two phase(air, dust). For turbulent flow, Reynolds stresses were closed by the standard $\kappa$-$\varepsilon$ model. The results are as follows ; 1) In the natural exhaust in the working place, the flows of the central region have a more rapid velocity vector than the right and left one. 2) Numerical results show that the distribution of contaminants concentration have greater influence on convection than the case of diffusion by government of velocity vectors. 3) To observe the velocity variation with distance, three location of distance are considered. As results, it shows that the velocity are 0.075(m/s) at y=5(m), 10(m) and mean concentration are raised 10.6% at y=5(m), 10(m). 4) We have presented the useful data for the adequate counterplan in the harmful working places by carrying out the various investigation of the natural ventilation.

• 에너지공학
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• 제2권3호
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• pp.268-275
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• 1993

수치해석 방법에 의해 큐백시의 스토커 소각로 유동장을 분석하였다. 수치모사의 변수는 큐백시의 스토커 소각로를 중심으로 한 5가지 내부 형상, 1차공기 속도, 2차공기 속도 및 주입각, 출구면적을 고려하였다. 검사체적에 기초한 Patankar의 유한차분 방법을 사용한 본 논문에서는 power-law scheme과 SIMPLEC 알고리즘을 사용했으며 난류 유동은 표준 k-e 모델을 이용했다. 소각로 유동장 분석을 위해서 재순환 영역의 크기, 난류 점성계수 및 이차공기의 질량분율 분포, 압력강하를 계산했다. 계산 결과는 물리적 의미에 잘 맞게 나타났으며, 큐백시의 스토커 소각로가 다른 내부 형상의 소각로에 비해 상부에 강한 난류를 가진 재순환 영역을 형성하였다.

• 한국산업융합학회 논문집
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• 제25권1호
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• pp.61-70
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• 2022

Fire damage time in high-rise buildings and wildland fire increasing every year. The use of high-pressure fire pumps is required to effectively extinguish fires. Reflecting the curvature effect of the fire hose occurring at the actual fire fighting site, this study provides a database of pressure drop, discharge velocity and maximum discharge height through C FD numerical analysis and it can provide using standards for fire extinguishing. Two Reynolds numbers of 200000 and 400000 were numerically analyzed at 0° -180° bending with water of 25℃ as a working fluid in hoses with a diameter of 65mm, a length of 15m, and a radius of curvature of 130mm. Realizable k-ε turbulence model was used and standard wall function was used. The pressure drop increases as the bending angle increases, and the maximum value at 90° and then decreases. The increasing rate is greater than the decrease. The velocity of the secondary flow also decreases after having the maximum value at 90°. The decreasing rate is greater than the increase. The turbulent kinetic energy increases to 120° and decreases with the maximum value. Pressure drop, velocity of the secondary flow, and turbulence kinetic energy are measured larger in the second bending region than in the first bending region.

• 한국전산유체공학회지
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• 제13권4호
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• pp.1-7
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• 2008

In the process of continuous hot-dip galvanizing, it is well known that the gas wiping through an air knife system is most effective because of its uniformity in coating thickness, possibility of thin coating, workability in high speed, and simplicity of control. However, gas wiping used in the galvanizing process brings about a problem of splashing at the strip edge above a certain high speed of process. It is also known that the problem of edge splashing is more harmful than that at the mid strip surface. For a given liquid(of a certain viscosity and surface tension), the onset of splashing mainly depends upon the strip velocity, the gas-jet pressure, and the nozzle's stand-off distance. In these connections in the present study, we proposed three kinds of air knife system having nozzles of constant expansion rate, and compared the jet structures issuing from newly proposed nozzle systems with the result by a conventional one. In numerical analysis, the governing equations are consisted of two-dimensional time dependent Navier-Stokes equations, and the standard k-${\varepsilon}$ turbulence model is employed to solve turbulence stress and so on. As the result, it is found that we had better use the constant expansion-rate nozzle which can be interpreted from the point view of the energy saving for the same coating thickness. Also, we better reduce the size of separation bubble and enhance the cutting ability at the strip surface, by using an air-knife having constant expansion-rate nozzle.

• 대한기계학회논문집B
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• 제23권10호
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• pp.1327-1339
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• 1999

Characteristics of two-phase flow and heat transfer were numerically investigated in a submerged gas Injection system. Effects of both the gas flow rate and bubble size were investigated. In addition, heat transfer characteristic and effects of heat transfer were investigated when temperature of the injected gas was different from that of the liquid. The Eulerian approach was used for the formulation of both the continuous and the dispersed phases. The turbulence in the liquid phase was modeled by the use of the standard $k-{\varepsilon}$ turbulence model. The interphase friction and heat transfer coefficient were calculated by means of correlations available in the literature. The turbulent dispersion of the phases was modeled by introducing a "dispersion Prandtl number". The plume region and the axial velocities are increased with increases in the gas flow rate and with decreases in the bubble diameter. The turbulent flow field grows stronger with the increases in the gas flow rate and with the decreases in the bubble diameter. In case that the heat transfer between the liquid and the gas is considered, the axial and the radial velocities are decreased in comparison with the case that there is no temperature difference between the liquid and the gas when the temperature of the injected gas is higher than the mean liquid temperature. The results in the present research are of interest in the design and the operation of a wide variety of material and chemical processes.

• 한국전자파학회논문지
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• 제23권2호
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• pp.251-257
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• 2012

인체 통신이란 사람의 몸통이나 피부를 전송 매질로 하여 데이터를 송수신하는 통신 방식을 의미한다. 본 논문에서는 인체 피부 표면에 닿아 있는 자유 공간을 전송 매체로 하여 데이터를 전달하는 전송 방식에 대하여, 10~30 MHz 주파수 범위에서 5 MHz 간격으로 5개의 주파수에 대하여 송수신부 사이의 전기장 분포에 대하여 수치 해석하였다. 채널 손실 계산은 총 29종의 조직으로 구성되어 있는 한국형 남성 표준 인체 모델에 상용의 툴을 사용하여 실행하였다. 계산 주파수에 따른 인체 조직의 도전율과 비유전율을 해석 파라미터로 입력하여 송수신부로 간주되는 손등 위에서 전기장 분포를 계산하였다. 손등에 부착된 송신기에 의한 전자파비(比)흡수율(SAR: Specific Absorbtion Rate) 값을 계산한 후, 국제비전리복사방호위원회(ICNIRP: International Commission on Non-Ionizing Radiation Protection) 인체 보호 기준과 비교하였다. 또한, 수치 해석으로 구한 전기장을 선(線)적분하여 인접한 극판들 사이의 전압들을 계산하였고, 송신부와 수신부의 전압의 비(比)를 채널 손실로 정의하였다. 수치 해석 결과, 10~30 MHz 주파수 대역에서 채널 손실의 범위는 약 ($75{\pm}1$) dB로 주파수에 따른 채널 손실의 변화가 크지 않았다.