• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.6
• /
• pp.768-773
• /
• 2012

This study was performed to find out the possibility that hot waste water from a thermoelectric power plant can be applied to Organic Rankine Cycle (ORC) by comparing the performance characteristics for use of the ocean surface water ($25^{\circ}C$) and hot waste water ($35^{\circ}C$) as a secondary fluid. The parameters considered in this study are four; superheating temperature, subcooling temperature, turbine efficiency, and pump efficiency. Main results of this study are summarized as follows : Overall efficiency of applying hot waste water to ORC is 87% higher than that of surface water. Thus it could be confirmed that hot waste water of the thermoelectric power plant can be applied to ORC.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.7
• /
• pp.753-757
• /
• 2012

This paper presents the performance of a porous glass electroosmotic pump using an iodide/triiodide aqueous solution. The porous glass electroosmotic pump is characterized in terms of the flow rate and voltage. The flow rate and voltage increases linearly with current. A point where the voltage significantly increases is observed owing to an excess in redox capacity. The transition time monotonously decreases with current. The normalized flow rate (flow rate per membrane surface area) is used to compare previous results with results obtained in this study. The normalized flow rate of porous glass frits is three times higher than that of Nafion 117.

• Aerospace Engineering and Technology
• /
• v.12 no.2
• /
• pp.108-117
• /
• 2013

The oxidizer shutoff valve of a gas generator controls the mass flow rate of the propellant of a rocket engine using pilot pressure and spring the force of the valve. The developing oxidizer shutoff valve can be shut off if the pilot pressure is removed from the actuator. Therefore, force balancing is necessary to analyze the characteristics of the forces with respect to the opening and closing of the valve in order to evaluate its performance. In light of this, the valve has been designed to adjust the control pressure required to open the poppet and to determine the working fluid pressure at which the valve starts to close. Under cryogenic flow test as a tests level of C.R.T(Control Random Test), the chattering phenomena occurred due to much leakage of a metal seat section. The pressure for chattering of the oxidizer valve is predicted at about 11 bar using force balancing analysis.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.7
• /
• pp.702-708
• /
• 2015

Two-phase flow boiling experiments were conducted using FC-72 as the working fluid. The micro-channels consisted of 15 channels with a depth of 0.2 mm, width of 0.45 mm, and length of 60 mm. Tests were performed over a mass flux range of $200-400kg/m^2s$, heat flux range of $5.6-49.0kW/m^2$, and vapor quality range of 0.02-0.93. Based on the results of the experiment, the heat transfer mechanism by nucleate boiling was dominant at a lower vapor quality (x<0.2), whereas that in the region of a vapor quality greater than 0.2 was complexly influenced by nucleate boiling and forced convection boiling. The nucleate boiling and forced convection boiling could be expressed as functions of the boiling number and convection number, respectively. In addition, the heat transfer coefficient obtained by the experiment was compared with the heat transfer coefficient by the existing correlation.

• Journal of Advanced Marine Engineering and Technology
• /
• v.37 no.8
• /
• pp.886-892
• /
• 2013

Hydraulic hose assemblies are used as piping components for construction machinery, automobile, aircraft, industrial machinery, machine tools, and machinery for ships. Then the reliability of hose assemblies is important because total hydraulic system, which used to deliver the fluid power ($P^*Q$) needed to flexibility in the piping system, is not operated if the hose assembly failed in the system. The data of the accelerated life test estimated through the shape parameter(${\beta}$) resulting of the Weibull distribution analysis. This study has tried to reduce the test time resulting from varying impulse pressure range and the flexing diameter. Accelerated life test model for the test results was adopted the GLL(generalized log linear) and the accelerated indexes are identified as 6.64 for the pressure and 4.46 for flexing radius. Also, it found that shape parameter is 6.19, scale parameter(${\eta}$) is $1.035{\times}108$, which were adopted the pressure 35 MPa and the flexing diameter R100 mm in the used condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.10
• /
• pp.833-839
• /
• 2013

Thermal vacuum test should be performed prior to launch to verify satellites' functionality in a harsh space environment which is represented by extremely cold temperatures and vacuum conditions. A thermal vacuum chamber which consists of a vacuum vessel, a pumping system, and a thermal control system are used to perform thermal vacuum tests of a satellite system and its components. A cryogenic blower is a core component of the closed loop thermal control system for thermal vacuum chambers. This paper describes the fan design of the cryogenic blower, the design of the thermal protection interface between the driving part and the fluid part, which were verified by thermal and structural analyses. The performance of the cryogenic blower is confirmed by similarity test on the test bench.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.2
• /
• pp.7-13
• /
• 2010

To satisfy the needs on fuel economy and engine performance, continuous variable valve lift systems are applying to engines. In the CVVL system, fuel economy can be improved by reducing pumping loss during the induction process, and engine performance can be also improved by controlling volumetric efficiency and the residual gas fraction. Because the residual gas fraction directly affects volumetric efficiency, engine performance, combustion efficiency and emissions in SI engines, controlling residual gas fraction is one of the important things in engine development process. This analysis investigates the residual gas fraction and volumetric efficiency with changes of intake valve lifts and intake valve timings. In this study, unsteady state solutions were solved during exhaust and induction processes. Results show variation of the residual gas fraction and volumetric efficiency by changing intake valve timing and lift. Decreasing intake valve lift leads to increase the residual gas fraction and to decrease volumetric efficiency.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.6
• /
• pp.613-619
• /
• 2016

A pneumatic control valve performs a major role in controlling the flow of a system or the level of a key tank in many power plants, and its performance should be guaranteed during the plant's lifetime. Its operation starts by supplying air to the pneumatic actuator or by exhausting the air from the actuator. To control the valve position, the amount of air supply or exhaust is adjusted by a control loop where various accessaries are equipped. In this paper, air leakage in the air supply line, changes in the valve packing force, and false adjustments of zero and the span of the positioner are simulated and analyzed using a 2-in pneumatic valve with a position control loop including an I/P converter and positioner, where the valve position is controlled within ${\pm}2%$ of the control pressure at 67% opening position.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.7
• /
• pp.797-803
• /
• 2012

Proportional solenoid valves are a modulating type that can control the displacement of valves continuously by means of electromagnetic forces proportional to the solenoid coil current. Because the solenoid-type modulating valves have the advantages of fast response and compact design over air-operated or motor-operated valves, they have been gaining acceptance in chemical and power plants to control the flow of fluids such as water, steam, and gas. This paper deals with the auto tuning of the position controller that can provide the proportional and integral gain automatically based on the dynamic system identification. The process characteristics of the solenoid valve are estimated with critical gain and critical period at a stability limit based on implemented relay feedback, and the controller parameters are determined by the classical Ziegler-Nichols design method. The auto-tuning algorithm was verified with experiments, and the effects of the operating point at which the relay control is activated as well as the relay amplitude were investigated.

• 한국신재생에너지학회:학술대회논문집
• /
• 2011.11a
• /
• pp.82.1-82.1
• /
• 2011

최근 국내에서 발생된 대규모 정전사태로 인해 안정적인 전력공급에 대한 국민들의 요구가 커져, 지난 3월 일본 후쿠시마 원전사고 이후 다시 한번 분산전원에 대한 필요성이 대두되어지고 있다. 여러 분산전원 중 연료전지는 다른 에너지원에 비해 에너지의 지속성이 우수하여 가장 안정적인 분산전원 형태의 하나이다. 이에 따라 국내의 경우 우수한 도시가스 인프라로 인해 건물용 연료전지라는 신기술에 대한 국민의 수용성은 점점 높아질 것으로 기대된다. 현재 건물용 연료전지의 경우, 주로 1kW급 연료전지가 시범보급되어 각 가정에 설치되어지고 있으나, 상가, 주유소 및 편의점 등의 상업시설과 생활관 및 소형빌라 등의 집단 주거시설 같은 1kW급 보다 용량을 더 필요로 하는 응용처에 국내에서 개발된 5kW급 연료전지시스템이 적용되어지기를 기대한다. 본 연구에서는 국내 제작된 5kW급 고분자전해질 연료전지시스템의 보급이전에 안전성능 평가를 통해 시스템의 성능 및 안전성 평가결과를 제조사에 피드백 하여 5kW급 건물용 연료전지시스템의 조기 상업화에 앞장서고자 한다. 5kW급 연료전지시스템의 기술개발은 핵심부품인 연료변환기, 스택 및 BOP 기술의 경우 1kW급 연료전지시스템에 적용된 것과는 다른 기술이 필요하고, 단순한 scale-up 과정이 아닌 새로운 기술개발로 제품에 적용시켜야 하는 난점을 가지고 있다. 특히, 연료변환기의 경우 연료 유량의 증가로 인하여 reformer, CO shift 및 Prox 반응기의 유체역학, 열교환 흐름 및 촉매반응 공학적으로 이론을 응용한 새로운 반응기 설계와 제작기술 확립이 선행되어 전체적인 시스템 제작 설계에 반영되어져야 한다. 그러므로 본 연구에서는 연료전지시스템 안전성능 평가를 위해 용량증대에 따른 안전성평가 항목을 검토하고, 5kW급 연료전지시스템평가를 수행하여 시스템의 제품성능, 작동성능 및 계통연계성능에서의 안전성을 확인하였고, 정전 유풍과 같은 이상조건 및 실외 환경에 대한 시스템의 안전성도 확인하였다. 또한 부하운전 조건을 75% 및 50%로 변화시켰을 때 빠른 응답시간과 안정적인 부하변동운전을 확인하였다.