• 대한의용생체공학회:의공학회지
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• 제28권4호
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• pp.449-454
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• 2007

An electrohydraulic (EH) pump-driven closed-loop blood pressure regulatory system was developed based on flow-mediated vascular occlusion using the vascular occlusive cuff technique. It is very useful for investigating blood pressure-dependant physiological variability, in particular, that could identify the principal mediators of renal autoregulation, such as tubuloglomerular feedback (TGF) and myogenic (MYO), during blood pressure regulation. To address this issue, renal perfusion pressure (RPP) should be well regulated under various experimental conditions. In this paper, we designed a new EH pump-driven RPP regulatory system capable of implementing precise and rapid RPP regulation. A closed-loop servo-controlwas developed with an optimal proportional plus integral (PI) compensation using the dynamic feedback RPP signal from animals. An in vivo performance was evaluated in terms of flow-mediated RPP occlusion, maintenance, and release responses. Step change to 80 mmHg reference from normal RPP revealed steady state error of ${\pm}3%$ during the RPP regulatory period after PI action. We obtained rapid RPP release time of approximately 300 ms. It is concluded that the proposed EH RPP regulatory system could be utilized in in vivo performance to study various pressure-flow relationships in diverse fields of physiology, and in particular, in renal autoregulation mechanisms.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.99-104
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• 1996

The jet pump is being used in many fields for several purposes because of its simple construction and easy operation. The characteristics of the geometrical variables, pressure gradient and velocity distribution of the jet pump are studied using the CFD technique. The flow calculations through a bended nozzle. a mixing chamber and a venturi are presented and phenomenological aspects are discussed. This study solve 3-D steady incompressible Navier-Stokes equations using the Iterative time marching scheme. The governing equations are differenced with 1st-order accurate backward difference scheme for the time derivatives and 3rd-order accurate QUICK scheme for the convective terms. The Mark-and-cell concept was applied efficiently to solve continuity equation, which is differenced 2nd-order accurate central differenced scheme. The 4th-order artificial damping is added to the continuity equation for numerical stability. A O-type of grid system is generated inside a nozzle and venturi of the jet pump. It has concluded that the results of present study properly agree with physical flow phenomena.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.643-648
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• 2001

The direct simulation Monte Carlo(DSMC) method is applied to investigate steady and unsteady flow fields of a single-stage disk-type drag pump. Two different kinds of pumps are considered: the first one is a rotor-rotor combination, and the second one is a rotor-stator combination. The pumping channels are cut on a rotor and stator. The rotor and stator have 10 Archimedes' spiral blades, respectively. In the present DSMC method, the variable hard sphere model is used as a molecular model, and the no time counter method is employed as a collision sampling technique. For simulation of diatomic gas flows, the Borgnakke-Larsen phenomenological model is adopted to redistribute the translational and internal energies. The DSMC results are in good agreement with the experimental data.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.185-190
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• 2001

The cavitation causes suction performance and efficiency of the high-speed pump to be reduced significantly To diminish these effects, the inducer has been used. Most of the inducer is designed at a maximum efficiency point of the pump, therefore suction performance drop due to effects of flow separation and inlet inverse flow is often observed at off-design point. The objective of this study is to find out the cavitation modes at various conditions by applying event detection technique and to design an inducer reducing cavitation. The pressure fluctuations at each cavitating condition were measured at inducer inlet and outlet locations using pressure transducers, which were located 90 degrees apart from each other to identify the cavitation modes. The time-frequency characteristics were analyzed by using Choi-williams distribution. In the second part of this paper, the inducer design method which uses nominal performance characteristic and onset condition of cavitation is introduced and applied to real situation.

• 대한기계학회논문집B
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• 제28권12호
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• pp.1501-1510
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• 2004

The pumping characteristics of a single-stage disk-type drag pump (DTDP) are calculated for the variation of the vertical clearance between a rotor and stator by the three-dimensional direct simulation Monte Carlo (DSMC) method. The gas flow mainly belongs to the molecular transition flow region. Spiral channels of a DTDP are cut on the both the upper and lower sides of a rotating disk, but a stationary disk is planar. The interaction between molecules is described by the variable hard-sphere model. The no time counter method is used as a collision sampling technique. The vertical clearance has a significant effect on the pumping performance. Experiments are performed under the outlet pressure range of 0.4∼533 Pa. When the numerical results are compared with the experimental data, the numerical results agree well quantitatively

• 한국유체기계학회 논문집
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• 제11권3호
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• pp.14-21
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• 2008

A numerical simulation on the flow field of a valveless bidirectional piezoelectric micropump has been performed. In this type of micropump, the oscillation of the piezoelectric diaphragm generates the blowing and suction flow through the oblique channel from the pumping chamber. The angle between the oblique and main channel causes the variation of flow distribution through upstream and downstream channels in suction and blowing modes. In the suction flow mode, the working fluid flows from both the upstream and downstream of the main channel to the pumping chamber through the oblique channel. However, in the blowing flow mode, the fluid pushed out of the pumping chamber flows more toward the downstream of the main channel due to the inertia of the fluid. In the present study, the effects of geometries such as the angle of oblique channel and the shape of main channel on the flow rate of the up/downstream were investigated. The flow rate obtained from the pump and the energy required to the pump were also analyzed for various displacements and frequencies of the oscillation of the diaphragm.

• 한국지반공학회논문집
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• 제20권3호
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• pp.47-51
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• 2004

불포화 투수계수함수는 흙수분 특성곡선과 함께 불포화토를 이해 연구하는데 있어서 없어서는 안 될 중요한 요소이다. 일반적으로 불포화 투수계수함수를 직접 측정하기에는 많은 어려움이 있기에, 흙수분 특성곡선에 근거한 예측함수를 사용하여 불포화 투수계수함수를 구하곤 했다. 본 연구에서는 이러한 예측함수를 사용하지 않고, 피스톤 펌프기법과 역해석 기법을 이용한 불포화 투수계수함수를 구하는 방법을 제시한다. 이렇게 구해진 불포화 투수계수함수는 예측함수를 사용하지 많았기 때문에, 흙수분 특성곡선으로부터 독립적이며 예측함수를 사용한 경우보다 보다 정확한 불포화토의 특성을 보여준다.

• 대한기계학회논문집A
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• 제32권9호
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• pp.720-727
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• 2008

Microfluidic single chip integrating thermopneumatic micropump and micro check valve are developed. The micropump and micorvalve are made of biocompatible materials, glass and PDMS, so as to be applicable to the biochip. By using the passive-type check valve, backward flow and fluid leakage are blocked and flow control is stable and precise. The chip is composed of three PDMS layers and a glass substrate. In the chip, flow channel and pump chamber were made on the PDMS layers by the replica molding technique and pump heater was made on the glass substrate by Cr/Au deposition. Diameter of the pump chamber is 7 mm and the width and depth of the channel are 200 and $180{\mu}m$, respectively. The PDMS layers chip and the heater deposited glass chip are combined by a jig and a clamp for pumping operation, and they are separable so that PDMS chip is used as a disposable but the heater chip is able to be used repeatedly. Pumping performance was simulated by CFD software and investigated experimentally. The performance was the best when the duty ratio of the applied voltage to the heater was 33%.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.451-454
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• 2006

Fiber optic distributed temperature sensing and thermal line sensor are applied in an observation borehole and a loom deep borehole heat exchanger. For the case of permanently installed system fiber optic DTS is very useful. By comparing with TLS, fiber optic DTS shows good accuracy and reliability. Ground water flow can give influences at heat exchange rate of the heat pump system. According to the hydraulic characteristics and temperature-depth profile, we consider that temperature-depth profile do not seem to be dependent on ground water flow. A permanent installation of fiber optic cable is expected as a reliable temperature measurement technique in a borehole heat exchanger system.

• 대한설비공학회지:설비저널
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• 제16권1호
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• pp.74-80
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• 1987

Turbulent convective heat transfer phenomenon which occur around the evaporator section of heat pump were analyzed experimentally. For this purpose a special wind tunnel and a heat pump system were designed and fabricated. Evaporator section was installed perpendicular to air flow direction and part of the evaporator was made of a glass tube for visual observation. The velocity distribution, turbulent intensity and temperature distribution were measured by hot wire technique and thermocouples. An experimental correlation for the convective heat transfer coefficient was obtained and the result is somewhat higher than the value calculated from Hilpert equation. The difference in two equations is believed to be due to the boning effect inside the evaporator tube.