• International Journal of Fluid Machinery and Systems
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• 제2권2호
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• pp.165-171
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• 2009

We developed a 'multi-point vibration acceleration method' for accurately predicting the cavitation intensity in pumps. Pressure wave generated by cavitation bubble collapse propagates and causes pump vibration. We measured vibration accelerations at several points on a casing, suction and discharge pipes of centrifugal and mixed-flow pumps. The measured vibration accelerations scattered because the pressure wave damped differently between the bubble collapse location and each sensor. In a conventional method, experimental constants are proposed without evaluating pressure propagation paths, then, the scattered vibration accelerations cause the inaccurate cavitation intensity. In our method, we formulated damping rate, transmittance of the pressure wave, and energy conversion from the pressure wave to the vibration along assumed pressure propagation paths. In the formulation, we theoretically defined a 'pressure propagation coefficient,' which is a correlation coefficient between the vibration acceleration and the bubble collapse pressure. With the pressure propagation coefficient, we can predict the cavitation intensity without experimental constants as proposed in a conventional method. The prediction accuracy of cavitation intensity is improved based on a statistical analysis of the multi-point vibration accelerations. The predicted cavitation intensity was verified with the plastic deformation rate of an aluminum sheet in the cavitation erosion area of the impeller blade. The cavitation intensities were proportional to the measured plastic deformation rates for three kinds of pumps. This suggests that our method is effective for estimating the cavitation intensity in pumps. We can make a cavitation intensity map by conducting this method and varying the flow rate and the net positive suction head (NPSH). The map is useful for avoiding the operating conditions having high risk of cavitation erosion.

• International Journal of Automotive Technology
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• 제8권2호
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• pp.219-224
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• 2007

Recently, atmospheric contaminations has become worse due to the increased number of automobile. The PCV (Positive Crankcase Ventilation) valve acts as a flow control to allow re-combustion of blow-by gas by having it flow from a crankcase to an inlet manifold suction tube. Also, during the fabrication of the PCV valve, micro cracks may occur in the valve body and be extended under operation. The excessive stress distribution and crack initiation on the PCV valve body would bring an unstable blow-by gas flow rate control and would cause valve failure. The purpose of this study is to examine the crack affects on the stress and strain variations on the PCV valve according to the inlet and outlet manifold under differential pressures. From the results, we can explain the behavior of the crack extension for a safe condition of PCV valve.

• KSBB Journal
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• 제4권1호
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• pp.57-61
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• 1989

발효액에서 hollow fiber membrane에 의한 Pichia sti-pitis의 분리 공정의 가능성을 검토해 보았다. Permeateflux는 cell의 농도, pH, antifoam agent의 농도, 여과 압력, 그리고 recircultion rate에 의해 영향을 받았으며 온도는 flux의 감소와 별로 관계가 없는 것으로 나타났다. 아울러 microcomputer에 조절되어 membrane을 backflush하는 것이 memnrane의 fouling 문제를 경감 시켜서 발효액에서 P. stipitis를 분리하는 공저의 연장된 조업을 가능케 함을 확인 하였다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.287-290
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• 2006

Orbiter mechanism has been applied to vacuum pump design for small oxygen generator where low vacuum of about 200mmHg is required. Performance of the designed vacuum pump has been numerically investigated: calculated volumetric and adiabatic efficiencies were 69.7% and 83.9%, respectively for leakage clearance of $10{\mu}m$. Total efficiency of the orbiter vacuum pump was 77.5%. At the shaft speed of 1700 rpm suction displacement volume of 6.3cc provided discharge flow at the rate of 2.3 liter/min with power consumption of 10.1Watt. Torque variation of the orbiter pump was only about 20% of that of diaphragm pump.

• 한국전산유체공학회지
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• 제8권1호
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• pp.1-7
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• 2003

The present study has conducted the analysis of flows in a blower with double suction. The air handling system is for supplying air flows into a plant. The present system has a couple of impellers in axial direction for enhanced flow rate. Main interest lies on the improvements of static pressure rise and total efficiency of the system. The present treatment of the reform is to secure a spatial distance between the fan and the casing of the system and change the shape of the cut-off part. The resultant performance after the reform shows increased pressure-rise and efficiency of the system

• 한국유체기계학회 논문집
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• 제9권5호
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• pp.28-35
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• 2006

Orbiter mechanism has been applied to vacuum pump design for small oxygen generator where low vacuum of about 200 mmHg is required. Performance of the designed vacuum pump has been numerically investigated: calculated volumetric and adiabatic efficiencies were 69.7% and 83.9%, respectively for leakage clearance of $10{\mu}m$. Total efficiency of the orbiter vacuum pump was 77.5%. At the shaft speed of 1700 rpm suction displacement volume of 6.3cc provided discharge flow at the rate of 2.3 liter/min with power consumption of 10.1Watt. Torque variation of the orbiter pump was only about 20% of that of diaphragm pump.

• 한국전산유체공학회지
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• 제20권1호
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• pp.77-83
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• 2015

Flow characteristics of synthetic jet based flow supplying devices have been computationally investigated for different device shapes. Jet momentum was produced by the volume change of a cavity by two piezoelectric-driven diaphragms. The devices have additional flow path compared with the original synthetic jet actuator, and these flow path changes the flow characteristics of synthetic jet actuator. Four non-dimensional parameters, which were functions of the shapes of the additional flow path, were considered as the most critical parameters in jet performance. Comparative studies were conducted to compare volume flow rate and jet velocity. Computed results were solved by 2-D incompressible Navier-Stokes solver with k-w SST turbulence model. Detailed computations revealed that the additional flow path diminishes suction strength of the synthetic jet actuator. In addition, the cross section area of the flow path has more influence over the jet performances than the length of the flow path. Based on the computational results, the synthetic jet based flow supplying devices could be improved by applying suitable shape of the flow path.

• 한국항공우주학회지
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• 제44권10호
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• pp.843-852
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• 2016

실제 씨앗의 3차원 형상과 운동요소에 기반하여 단풍나무(Acer palmatum 종) 씨앗의 자동회전 비행을 수치적으로 해석하였다. 운동요소의 표준 값은 낙하속도는 1.26 m/s, 회전속도는 133.6 rad/s (1,276 rpm), 코닝 각은 $19.4^{\circ}$, 피치 각은 $-1.5^{\circ}$이다. 씨앗 날개의 스팬 안쪽에 위치한 컴팩트한 앞전 와류가 씨앗 날개 바람 반대면에 커다란 부압을 발생하게 하였다. 부압의 피크는 안쪽 스팬 단면 앞전 부근에 발생하였다. 본 연구에서 얻어진 현저한 앞전 와류로 특징되는 흐름 형태와 공기력 계수의 값은 동적 상사를 갖도록 한 로봇 씨앗에 대하여 실험적으로 측정한 자료와 잘 일치하였다. 바람 반대 영역에 발달한 나선형 와류는 씨앗 끝을 향하여 전진하고 씨앗 끝 부분에서 이곳을 지나는 흐름과 합쳐지는데, 이와 같은 흐름이 자동회전하는 단풍나무 씨앗의 안정되고 부착된 LEV를 유지하게 하는 메카니즘으로 여겨진다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권6호
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• pp.869-876
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• 2008

A thermocompressor is the equipment which compresses a vapor to a desired discharge pressure. Since it was first used as the evacuation pump for a surface condenser, it has been widely adopted for energy saving systems due to its high working confidence. In the present study, the geometrical analysis of the shape between the jet nozzle and the diffuser inlet, the drag force was calculated by means of the integrated equation of motion and the computational fluid dynamic (CFD) package called FLUENT. The computer simulations were performed to investigate the effects by the various suction flow rates, the distance from jet nozzle outlet to the diffuser inlet and the dimensions of the diffuser inlet section through the iterative calculation. In addition, the results from the CFD analysis on the thermocompressor and the experiments were compared for the verification of the CFD results. In the case of a jet nozzle, the results from the CFD analysis showed a good agreement with the experimental results. Furthermore, in this study, a special attention was paid on the performance of the thermocompressor by varying the diffuser convergence angle of $0.0^{\circ}$, $0.5^{\circ}$, $1.0^{\circ}$, $2.0^{\circ}$, $3.5^{\circ}$ and $4.5^{\circ}$. With the increase of the diffuser convergence angle. the suction capacity was improved up to the degree of $1.0^{\circ}$ while it was decreased over the degree of $1.0^{\circ}$.

• 한국유체기계학회 논문집
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• 제13권1호
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• pp.42-51
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• 2010

Many different types of fan have been applying to various industrial fields. Fan design methods are much different depending on the types of fan, operating conditions, and connecting parts at the inlet or exit of the fan etc. In this study, design methods for an axial-type suction fan are studied. This fan discharges the air in the relative static pressure of -285Pa to the atmosphere with the flow rate of $960m^3/min$. For three-dimensional blade design, three different design methods were applied, such as the free vortex method, the exponential method, and the cascade method. In the cascade method, the blade loading along the radial direction was obtained from the lift coefficient which was necessary to obtain the pressure rise on a fan rotor. This method is different from the free vortex and the exponential method which control the strength of the vortex. The fan performance prediction was conducted using the CFD with three different inlet ducts. The best fan performance was obtained when the fan was designed by using the cascade method. The designed fan using the exponential method showed better performance compared to a fan designed using the free vortex method. However, the fan performance was changed depending on the installed inlet ducts. So, an efficient fan can be designed with the adjustment of design variables on the basis of the flow structures within the fan as well as the fan design procedure.