• International Journal of Fluid Machinery and Systems
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• v.10 no.3
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• pp.307-317
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• 2017

In liquid-propellant rockets, POGO instability can occur, in which a fluctuation of propellant supply to the engine, a thrust fluctuation, and a structural vibration are coupled. For the prediction of this instability, it is required to provide dynamic characteristics of the pump represented as the transfer matrix correlating the upstream and downstream pressure and flow rate fluctuations. In the present study, the flow rate fluctuation is evaluated from the fluctuation of pressure difference at the different locations assuming that the fluctuation is caused by the inertia of the flow rate fluctuation. The experiments were performed in some flow conditions, and it was shown that the tendencies of dynamic characteristics are related to excitation frequencies, cavitation numbers and flow rate coefficients.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.5
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• pp.171-177
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• 2016

Plate heat exchangers have been widely used in various fields because of their high heat transfer coefficients, small area of installation, and ease of maintenance compared to other heat exchangers. However, when plate heat exchanger is used for a long time, leak can occur due to inner crack. Therefore, it is important to understand the inner flow characteristics in plate heat exchangers. In this study, the inner flow characteristics and flow rate of plate heat exchanger were evaluated using various flow directions, pin-hole sizes, and Reynolds numbers. In downflow, initially most water flowed to the opposite of the inlet due to distribution region. Then it gradually had a uniform distribution due to chevron configuration. In upflow, it had a uniform flow consistently due to the dominant gravity effect. As the Reynolds number increased, the leak rate was decreased due to the inertia effect regardless of the flow direction.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.275-280
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• 1997

We have investigated the deposition characteristics of (Ni0.8Fe0.2)20Ag80 thin films as a function of chamber pressure and nitrogen flow rate with scanning electron microscopy(SEM), atomic force microscopy(AFM), XRD and $\alpha$-step. The deposition rate of these film is decreased with increasing the chamber pressure and the nitrogen flow rate. With raising the chamber pressure, the growth mode of thin film is changed from island growth to columnar one, which is probably due to energy of atom. Contrary, the nitrogen flow rate is raised, growth mode is changed from columnar to island one. According to the XRD patterns, the preferred orientation is inhibited as the nitrogen flow rate is kept above 10 sccm, but that is nearly independent on the chamber pressure. When the chamber pressure decrease or the nitrogen flow rate increase, phase separation into permoally and silver is occured.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.25-28
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• 2004

The purpose of this paper is to present essential numerical data of FCV(Flow rate Control Valve) which is used in a projectile ejection system for a underwater vehicle. A commercial CFD code is applied to analyze the 3 dimensional viscous compressible flow field within the FCV as four cases of opening rate, 25, 50, 75, and $100\%$. The flow coefficient of each cases are mainly calculated. And other characteristics such as the location of shock wave and total temperature distribution are also determined.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.2
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• pp.124-130
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• 1999

Flow characteristics of a compressible gas flow through a rotating disc-type rotary valve are investigated experimentally under various conditions. It is known that the mass flow rate through poppet valves of 4-stroke cycle engines and through piston valves of 2-stoke cycle engines decrease with increase in engine speed. Rotary valve is one means by which air may be made to flow inter-mittently through a pipe. In this paper an exhaust system simulator of engine was used to experi-mentally analyze the decrease in flow rate at high rotation speeds and to determine what variables other than rotational speed give rise to the observed behaviour. These variables have been included in an empirical equation which is representative of the measured flow characteristics.

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.262-271
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• 2004

Hydropneumatic suspension unit is an important part of tracked vehicles to absorb external impact load exerted from the non-paved road and the cannon discharge. Its absorption performance is strongly influenced by both damping and spring forces of the unit. In this paper, we numerically analyze the damping characteristics of the in-arm-type hydropneumatic suspension unit (ISU) by considering four distinct dynamic modes of the ISU damper: jounce-loading, jounce-unloading, rebound-loading and rebound-unloading. The flow rate coefficients determining the oil flow rate through the damper orifice are decided with the help of independent experiments. The wheel reaction force, the flow rate at cracking and the damping energy are parametrically investigated with respect to the orifice diameter and the wheel motion frequency.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.6
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• pp.82-91
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• 2021

We compared the heat transfer characteristics of the parallel and the counterflow flow in the concentric double tube of the Al₂O₃/water nanofluids using numerical methods. The high- and low-temperature fluids flow through the inner circular tube and the annular tube, respectively. The heat transfer characteristics according to the flow direction were compared by changing the volume flow rate and the volume concentration of the nanoparticles. The results showed that the heat transfer rate and overall heat transfer coefficient improved compared to those of basic fluid with increasing the volume and flow rate of nanoparticles. When the inflow rate was small, the heat transfer performance of the counterflow was about 22% better than the parallel flow. As the inflow rate was increased, the parallel flow and the counterflow had similar heat transfer rates. In addition, the effectiveness of the counterflow increased from 10% to 22% rather than the parallel flow. However, we verified that the increment in the friction factor of the counterflow is not large compared to the increment in the heat transfer rate.

• Journal of Biosystems Engineering
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• v.20 no.1
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• pp.58-65
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• 1995

A numerical study for a two dimensional multi-jet with crossflow of the spent fluid has been carried out. Three different distributions of mass-flow rate at 5 jet exits were assumed to see their effects upon the flow characteristics, especially in the jet-flow region. For each distribution, various Reynolds numbers ranging from laminar to turbulent flows were considered. Calculations drew the following items as conclusion. 1) The development of the free jets issued from downstream jets was hindered by the crossflow formed due to jets. Consequently, the free jet was developed into the channel flow without any evident symptom of impingement jet flow characteristics 2) The crossflow induced the pressure gradient along the cross section of jet exits and the value of the pressure gradient increased as going downstream. The crossflow generated also the turbulent kinetic energy as it collied with the downstream jets. 3) The skin friction coefficient along the impingement plate was affected more by the distribution of mass flow rate at jet exits rather than by the Reynolds number. The skin friction coefficient was inversely proportional to the square root of the Reynolds number, regardless of flow regime when a fully developed flow was formed in the jet flow region. 4) The distribution of the skin friction coefficient along the impingement plate was found to be controlled by adjusting the distribution of mass flow rate at jet exits.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.880-885
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• 2000

Flow patterns and steady flow characteristics of an intake 3valve cylinder head are not obviously declared. Thus, in the study, the characteristics and limitation of intake flow coefficient which applied to multi intake valve engine are introduced. The flow coefficient and tumble characteristics are investigated by means of the steady flow test and flow visualization method. As the results, it is found that the intake flow rate is dominated by effective valve open area. In addition, this paper shows that the mass flow rate of intake 3valve engine is greater than that of intake 2valve engine and tumble flow of intake 3valve engine is superior to that of intake 2valve engine.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.1
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• pp.78-83
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• 2003

Electro-rheological(ER) fluids are suspensions in which rheological properties show an abrupt change with variation of electric fields. We modeled the parallel-plates relating to ER-Valve system and yielded shear stress according to the strength of electric field. The purpose of the present study is to examine the flow characteristics of ER fluids according to the strength of electric field between parallel-plates. Then the steady relationship between pressure drop and flow rate of the ER fluids between parallel-plates under application of an electric fields was measured. The pressure drop and flow rates of ER fluids under the application of electric fields for steady flow were measured. For the experiment, we used the ER fluids, 35w% zeolite having hydrous particles and differential pressure gauge. This test reviewed experiment for the special changes of ER fluids in the steady flow condition.