• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.638-641
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• 2008

Computational investigation was conducted to study the effects of the shape parameter of shroud on the performance of the outdoor unit of an air-conditioners. For this study the Design of Experiment(4-factor 3-level) was created and the an automatic program was composed using VBA to reduce the load of pre-process for CFD. The estimated mathematical equation was produced from this analysis and it was found that the gap between fan and shroud affects more heavily than the other parameters. As a result, the composition of the best parameters was verified that its flow rate was increased by 10 percents and sound pressure level was reduced by 1.2 dBA compare with the worst. And finally, a kind of Propeller fan with blades which were attached to the shroud, so-called 'ProBeller Fan' was introduced in this study.

• Proceedings of the KSME Conference
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• 대한기계학회 2003년도 추계학술대회
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• pp.816-821
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• 2003

The pumping characteristics of a disk-type drag pump (DTDP) from free molecular flow region to the slip flow region are calculated by the direct simulation Monte Carlo (DSMC) method. In this study, the pumping performance is studied numerically for several channel depths. The interaction between molecules is modeled by variable hard-sphere (VHS). The no time counter method is used as a collision sampling technique. The clearance between rotor and stator is considered an effect on performance. Spiral channels are cut on both upper and lower sides of rotating disks, and stationary disks are planar. A three-dimensional DSMC method for the analysis of steady rarefied flows in a single-stage DTDP has been developed. Velocity and density fields were obtained by the DSMC simulation in the rotor. The present experimental data in the outlet pressure range of $7.5{\times}10^{-3}{\sim}4$ Torr were compared with the DSMC results in the single-stage DTDP. Comparison between the experimental data and DSMC results showed good agreement.

• Transactions of The Korea Fluid Power Systems Society
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• 제4권3호
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• pp.1-6
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• 2007

The leakage generated from the clearance between the cylinder bore and the piston is one of the most serious problems in the hydraulic piston pump, and it even results in terrible decrease of the volume efficiency at a great velocity and high pressure. In this paper, the lubrication characteristic of the hydrostatic slipper bearing equipped in the hydraulic piston pump has been worked out by experimentation with three model bearings of different shape. Preparatory to this, not only the three models of piston-slipper were designed, but the corresponding experimental apparatus were also manufactured. As a result, it was verified that, according to the supply pressure, the hydrostatic bearing part of the slipper is severely affected by the pocket pressure, land pressure, oil film thickness, and leakage flow.

• Transactions of the Korean Society of Automotive Engineers
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• 제5권2호
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• pp.136-148
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• 1997

The present study has been carried out to develop a computational procedure for the analysis of the off-design performance in centrifugal compressors with vaneless diffusers by integrating empirical loss models and analytical equations. Losses in centrifugal compressors stem from a number of sources and their exact calculation is not yet possible. This study investigates several modeling schemes and shows that a fairly good prediction can be achieved by a proper selection of the most important flow parameters resulting form a meanline one-dimensional analysis. The performance maps for compressors are calculated and compared with measured performance maps. The off-design performance characteristics in terms of the pressure ratio vs. mass flow produced have generally correct forms. However, no universal means have been found to predict accurately the onset of surge. The prediction method developed through this study can serve as a tool to ensure good matching between parts and it can assist the understanding of the operational characteristics of general purpose centrifugal compressors.

• Transactions of The Korea Fluid Power Systems Society
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• 제1권2호
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• pp.8-14
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• 2004

Abstract: In the oil hydraulic piston pumps the clearance between the valve plate and cylinder block plays an important role for volumetric and overall efficiency. Thus, adequate lubricational fluid film is needed for the interface. In this study, fluid film thickness is measured by a gap sensor and a slip ring under operational conditions to observe the behavior of the lubrication mechanism in detail. To investigate the effect according to the valve plate types in view of the fluid film, three different types were designed. Leakage flow rate and shaft torque were also measured to clarify the effect according to the valve plate types. A broad range of experiments were conducted to provide reasonable data on the effect of fluid film. In this experiments two main parameters were found, of which the one is the discharge pressure and the other is valve plate geometry. As a result, we found that the spherical valve plate could get more stable fluid film thickness, maintain good efficiency for high pressure range than the other types.

• YAKHAK HOEJI
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• 제42권5호
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• pp.519-526
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• 1998

This study was performed in order to investigate the effect of renal function of NG-nitro-L-arginine (L-NOARG), inhibitor of nitric oxide (NO) synthase, in dog and ra bbit. L-NOARG, when given intravenously in dogs, exhibited the decrease in urine flow (vol), renal plasma flow (RPF), osmolar clearance ($C_{osm}$) and amounts of sodium and potassium excreted in urine($E_{Na},\;E_K$). These renal functions of L-NOARG showed the same aspect in rabbit, too. L-NOARG, when administered into a renal artery, showed the same pattern as was obtained when given intravenously in both experimental and control kidney in dog. L-NOARG administered into the carotid artery showed the decrease in Vol, RPF, $E_{Na}$, in a low doses that did not show any effect when given intravenously. Above results suggest that L-NOARG produces antidiuretic action in dog and rabbit, and these antidiuretic actions may be mediated by central action.

• YAKHAK HOEJI
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• 제27권4호
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• pp.271-282
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• 1983

This study is an attempt to study the influence of clonidine, which has a central sympatholytic action, on the renal function in dogs and to elucidate its mechanism of action. Clonidine ($15\mu$g/kg) injected into a cephalic vein of the dog produced a marked increase in urine flow and in amounts of $Na^{+}$ and $K^{+}$ excreted in urine, and clearances of free water and osmolar substance, the reabsorption rates of $Na^{+}$ and $K^{+}$ in renal tubules were significantly decreased. Clonidine ($50.0]mu$g/kg) administered intravenouly elicited a transient reduction in urine flow, along with inhibition of all renal functions. Intravenous clonidine-induced diuretic effect was completely blocked by pretreatment with reserpine, and was lessened by water diuresis. Clonidine ($3.0\mu$g/kg) injected tnto a carotid artery revealed a transient diuresis with a increase in clearance of free water. Clonidine injected into a renal artery showed a significant antidiuretic effect and all functions of an experimental kidney were reduced. Antidiuretic action induced by clonidine given into a renal artery markedly suppressed by pretreatment with reserpine. The above results suggest that clonidine has dual mechanisms: 1) diuretic effect due to the central sympatholytic action and inhibition of release of antidiuretic hormone, and 2) antidiutetic effect indued by indirect symptheic stimulation in the periphery.

• Transactions of the Korean hydrogen and new energy society
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• 제25권4호
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• pp.449-458
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• 2014

The heat transfer phenomenon was investigated in this study when a single round water jet with the low velocity and against the direction of gravity flows to the downward facing Isothermal of definite thickness circular plate. Experimental investigation is performed for a single round jet diameter 4mm, 6mm, and 8mm with the jet velocity 2.4m/s and jet fluid temperature of $24^{\circ}C$, varied the ratio of nozzle clearance/nozzle diameter (H/D)1, 2, 3, 6, and 8, on circular plate isothermal condition with $85^{\circ}C$. The local convection heat transfer coefficient distributions are analyzed based on the visualization of jet flow field. The effects of the diameter of Nozzle, the ratio of H/D and the ratio of nozzle diameter/circular plate diameter on heat transfer phenomenon are investigated. As a results of experiment is obtained correlation equation, $Nu_r=3.18Re_r^{0.55}Pr_r^{0.4}$.

• Tribology and Lubricants
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• 제28권5호
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• pp.218-232
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• 2012

In a spool valve analysis, the Reynolds equation is commonly used to investigate the lubrication characteristics. However, the validity of the Reynolds equation is questionable in a spool valve analysis because cavitation often occurs in the groove and the depth of the groove is much higher than the clearance in most cases. Therefore, the validity of the Reynolds equation in a spool valve analysis is investigated by comparing the results obtained from the Reynolds equation and the Navier-Stokes equation. Dimensionless parameters are determined from a nondimensional form of the governing equations. The differences between the lateral force, friction force, and volume flow rate (leakage) obtained by the Reynolds equation and those obtained by the Navier-Stokes equation are discussed. It is shown that there is little difference (less than 10%), except in the case of a spool valve with many grooves where no cavitation occurs in the grooves. In most cases, the Reynolds equation is effective for a spool valve analysis under a no cavitation condition.

• Journal of Mechanical Science and Technology
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• 제19권7호
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• pp.1478-1487
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• 2005

A small mixed-type turbine with a diameter of 19.9 mm has been substituted for a rotational part of pencil-type air tool. Usually, a vane-type rotor is applied to the rotational part of the air tool. However, the vane-type rotor has some problems, such as friction, abrasion, and necessity of accurate assembly etc.,. These problems make the life time of the vane-type air tool short, but air tools operated by mixed-type turbines are free of friction and abrasion because the turbine rotor dose not contact with the casing. Moreover, it is assembled easily because of no axis offset. These characteristics are merits for using air tools, but loss of power is inevitable on a non-contacting type rotor due to flow loss, tip clearance loss, and profile loss etc.,. In this study, four different rotors are tested, and their characteristics are investigated by measuring the specific output power. Additionally, optimum nozzle location against the rotor is studied. Output powers are obtained through measured pressure, temperature, torque, rotational speed, and flow rate. The experimental results obtained with four different rotors show that the rotor blade shape greatly influences to the performance, and the optimum nozzle location exists near the mid span of the rotor.