• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.310-315
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• 2008

In this study, experimental study on the heating performance of a $CO_2$ heat pump water heater with a variation of operating conditions such as refrigerant charge amount, outdoor temperature, compressor frequency, EEV opening and water mass flow rate. Based on the test results, the optimum charge amount was 1800 g. At the water mass flow rates of 75, 85, 95 kg/hr, the water heating temperature was 62, 67, $74^{\circ}C$ and COP was 2.6, 2.8, 3.0, respectively. Besides, the water mass flow rate and compressor frequency were varied to maintain above the water heating temperature of $60^{\circ}C$ with the decrease of outdoor temperature. So, The compressor frequency increased beyond 65 Hz and the water mass flow rate was 45 kg/hr at the outdoor temperature of $-13^{\circ}C$, 65 kg/hr at $-8^{\circ}C$, 75 kg/hr at $-3^{\circ}C$ and 85 kg/hr at 2, $7^{\circ}C$. As the outdoor temperature decreased, the heating COP decreased by 2.5-39.8%.

• Fire Science and Engineering
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• v.29 no.1
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• pp.53-59
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• 2015

Water hammering created by an unsteady flow in pipeline systems can cause excessive change in pressure, vibration, and noise. So, water hammer analysis is very important for limiting the damage caused to pipeline, pump and valve systems by operation conditions. On the other hand, water hammer arrester has been manufactured and used in order to minimize the damage caused by water hammering phenomenon in domestic, and it has been produced and installed as the low cost-oriented because of being no separate standard in the meanwhile. Therefore, our research team investigated about the standardization of water hammer arrester performance through the various methods, such as test methods for verification of one pipe, assuming the occurrence of water hammer in a water-based fire extinguishing system, separated for opening impact pressure and shut off impact pressure and for a branch pipe in order to make guideline for water hammer arrester performance. And finally, verified the performance of the water hammer pressure as the simple mechanical way using the U-shaped pipe and a test weight, so KFI standards for the water hammer arrester could be established.

• Journal of Chest Surgery
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• v.29 no.12
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• pp.1329-1336
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• 1996

From January, 1994 to January. 1996, mitral valve replacement was performed in 27 patients. Among these, 17 patients underwent mitral valve replacement(MVR) with preservation of the annulo-papillary continuity(PAPCMVR) (-Group I), and 10 patients underwent conventional methods of excision of all the chordae(Group II). The operative technique for PAPCM VR consists of the division of the anterior leaflet into anterior and posterior segments, shifting and reattachment of the divided segments to the mitral ring of the respective commissural areas. This retrospective study has been designed to evalute the postoperative left ventricular function in the two groups. In the group 1, LVEF(Left Vnetricular Ejection Fraction : %) was 52 $\pm$ 3 preoperatively And 50$\pm$3 postoperatively, LVESI Vent icular End Systolic Volume Index/mL/m2) wIns 59 :6 and 51 $\pm$ 7, LVEDI Ventricular End Diastolic Volume Index/mL/m2) was 124$\pm$ 11 and 91 :8. In the group II, LVEF was 56$\pm$1 and 47:), LVESVI 62$\pm$12 and 61$\pm$15, LVEDVI 133$\pm$27 and 104$\pm$17. : the variation of the LVEF in these two group was statistically different(p(0.05). A comparison of left ventricular function data between Group I(n: 17) and Group II(n: 10) revealed better results in echocardiographic LVEF(p<0.05), LVEDVI(p<0.01) in the former group. The mean functional class(UYHA) was 2.6 preoperative and improved to 1.0 postoperatively In group 1, and 2.8 and to 1.0 in group II. We conclude that maintenance of continuity between the mitral annulus and papillary muscles is expected to have a beneficial effect on postoperative left ventricular performance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.9
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• pp.822-829
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• 2015

In this paper, the piezoelectric-hydraulic pump with a piezostack actuator as a driving source has been designed, fabricated, and evaluated for its application to UAV's brake system. The performance requirements of the piezoelectric-hydraulic pump were decided based on the requirements analysis of the target aircraft brake system. The geometric design of the piezoelectric-hydraulic pump to meet the performance requirements of the pump was conducted, and all components of the pump including the spring sheet type check valves were machined with close tolerance. By constructing a test apparatus for the performance check of the piezoelectric-hydraulic pump, the performance characteristics of the pump, such as the outlet flow rate for load-free condition and the outlet oil pressure for closed loop condition, have been evaluated. It has been found by the performance test result that the developed piezoelectric-hydraulic pump satisfies the design requirements effectively.

• Aerospace Engineering and Technology
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• v.4 no.2
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• pp.65-70
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• 2005

The KOMPSAT program is carrying out successfully in spite of the short domestic space development history, but there are still many difficulties in Koreanization of most core parts. Because the development of core parts is essential to participate in the advanced nations in space based on the mid-long term national space program, KARI has carried out development of Fill/Drain valve for propellant/pressurant supply of satellite, which has high possibilities to be koreanized, with Hanwha Corp.. This paper summarizes overall processes of development including design, manufacturing and test, and finally 4 sets of modules were successfully made. Also the satisfaction of performance requirements are verified through acceptance tests.

• Journal of Mechanical Science and Technology
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• v.20 no.4
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• pp.447-454
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• 2006

Hydraulic actuators are important in modern industry due to high power, fast response, and high stiffness. In recent years, hybrid actuation system, which combines electric and hydraulic technology in a compact unit, can be adapted to a wide variety of force, speed and torque requirements. Moreover, the hybrid actuation system has dealt with the energy consumption and noise problem existed in the conventional hydraulic system. Therefore, hybrid actuator has a wide range of application fields such as plastic injection-molding and metal forming technology, where force or pressure control is the most important technology. In this paper, the solution for force control of hybrid system is presented. However, some limitations still exist such as deterioration of the performance of transient response due to the variable environment stiffness. Therefore, intelligent switching control using Learning Vector Quantization Neural Network (LVQNN) is newly proposed in this paper in order to overcome these limitations. Experiments are carried out to evaluate the effectiveness of the proposed algorithm with large variation of stiffness of external environment. In addition, it is understood that the new system has energy saving effect even though it has almost the same response as that of valve controlled system.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.5
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• pp.516-524
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• 2014

Proper discharge of nitrogen gas and water condensate is required in a conventional fuel cell system for performance, stability and durability of fuel cell stacks. Present study covers the development of integrated unit and its functioning logic for simultaneous nitrogen gas purge and water condensate drainage in a fuel cell vehicle system. Configuration of condensate drainage pipe, purge valve and level sensor is considered and optimized in physical integration. As a key factor, discharge time is considered and optimized based on the test result of constant-current operation with various operating temperature in logic development. Consequently, derived optimal values are applied and verified in actual vehicle drive mode test. Increase of system design flexibility, weight reduction and cost reduction are anticipated with this study. Additional study for physical and logical improvement is currently being implemented.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2839-2844
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• 2007

Micro hydraulic power generation of which the output is less or equal to a 100kW is attracting considerable attention. This is because of its small, simple, renewable, and abundant energy resources. By using a small hydropower generator of which main concept is based on using the different water pressure levels in pipe lines, energy which was initially wasted by use of a reducing valve at the end of the pipeline, is collected by turbine in the hydropower generator. A propeller shaped hydroturbine has been used in order to use this renewable pressure energy. In this study, in order to acquire basic design data of tubular type hydraulic turbine, output power, head, efficiency characteristics due to the flow coefficient are examined in detail. Moreover influences of pressure and velocity distributions with the variations of runner vane angle on turbine performance are investigated by using a commercial CFD code.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.89-90
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• 2002

Ball reducer (HERB Drive: High Efficient Wave Rolling Ball Drive) with waved grooves has many advantages over other types of reducers for high-reduction ratio, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in contact behaviors. In this study, we have investigated the traces of contact between ball and outer ring, and the dynamic contact behaviors of elastohydodynamic lubrication(EHL) with a certain reduction ratio. In order to verify the contact behaviors between ball and outer ring for the critical endurance lift, the contact velocity and load are computed for a cycle. During some intervals of a cycle, the contact velocity reverses its direction very suddenly. It is expected that changing the contact direction causes undesirable endurance performance because EHL film frequently col lapse at the moment of velocity reversal. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very typical in many contact phenomena.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.3
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• pp.439-445
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• 2013

This study is on the system that can integrate generator and charger to use as a welder and generator for need. Specifically, it was hybrid generator consisted with select switch to use generator controller and multiple function welder, that function were auto-stopping generator when generator power finish to recharge in recharger battery and Co2 MMA TIG MIG MAG are devide depend on supplying gas. This control system of voltage, high-frequency, motor and gas valve was implemented in order to improve the performance and convenience of existing welders to choose only one or two at a time.