• 한국산학기술학회논문지
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• 제16권1호
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• pp.50-55
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• 2015

본 연구에서는 공동 주택의 수전 개방 조건에서, 감압밸브 내부 오리피스 형상이 캐비테이션 발생에 미치는 영향에 대하여 살펴보았다. 이를 위하여 감압밸브 내부의 유로형상을 9가지 유형으로 구별하여 제시하고, 3차원 유한해석 코드인 ANSYS CFX를 사용하여 감압밸브 내의 유동해석을 수행하였다. 급격한 단면 변화가 일어나는 오리피스에서 최저 압력과 최대 속도가 발생하였다. 최대속도가 존재하는 부위에서 0 이상 증기체적비를 나타내어 캐비테이션이 발생함을 확인하였다. 유로 길이가 긴 형상에 비하여 돌연 확대관 형상의 모델에서 유체의 최대 속도가 낮게 나타났다. 돌연확대관 형상의 경우에는 매우 작은 증기체적비를 나타내고 있으며, 돌연확대의 정도가 클수록 증기체적비는 낮게 나타났다. 따라서 감압밸브의 케비테이션 발생을 방지하기 위해서는 돌연확대의 형상을 갖도록 설계하는 것이 타당하다고 판단된다.

• 한국수소및신에너지학회논문집
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• 제32권4호
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• pp.205-211
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• 2021

Recently, it is necessary for study on renewable energy due to environmental pollution and fossil fuel depletion. Therefore, in this study, the filling temperature according to the nozzle geometry was evaluated based on the limit temperature specified in SAEJ2601 for charging hydrogen, a new energy. There are three types of nozzles, normal, angle and round, fixed the average pressure ramp rate at 52.5 MPa/min, and the injection temperature was set at 293.4 K. As a result, the lowest temperature distribution was found in the round type, although the final temperature did not differ significantly in the three types of nozzles. In addition, Pearson's coefficient was calculated to correlate the mass flow rate with the heat transfer rate at the inner liner wall, which resulted in a strong linear relationship of 0.98 or higher.

• KIEAE Journal
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• 제12권6호
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• pp.23-28
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• 2012

Pressure distribution in the water supply system of an apartment complex consisting of 12 buildings and 635 units in total have been investigated numerically. The complex incorporates two zone booster pump system, and around a half of units have pressure reducing valves (PRVs) in them. Calculated hydrostatic pressure without the water flow were compared with their designed and measured counterparts, and they agreed quite well with each other. Then, the pressure and volumetric water flow rate at all units were analyzed, indicating that there are noticeable differences in pressure and flow rate in one unit to another, although the aforementioned minimization technologies of pressure deviation were employed. In order to further reduce the difference in the water flow rate, it is suggested that all the units in the complex have PRVs installed in their water supply system. The effect of setting pressure of the PRVs on the non-uniformity of the flow in each unit and on the reduction of total water supply for the apartment complex have been studied. With the same PRV setting pressure of 3.952 bar (or the gauge pressure of $3.0kg_f/cm^2$), it has been estimated that the suggested system improves the non-uniformity (the coefficient of variation) of the flow rate of apartment complex over the current system, from 8.02% to 6.66%, and reduces the total water supply, from $0.02804m^3/s$ to $0.02766m^3/s$.

• Journal of Advanced Marine Engineering and Technology
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• 제29권8호
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• pp.946-952
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• 2005

The $CO_{2}$ refrigeration cycle is expected to reduce the compressor work and increase the COP by applying two-phase ejector as a device for the recovery of dissipated expansion energy. In this study, the performance of the cycle was simulated and effects of the ejector shapes on the performance of the $CO_{2}$ refrigeration cycle were investigated. The following results were obtained through the cycle simulation. The COP of the $CO_{2}$ refrigeration cycle with two-phase ejector flow which expansion is occured in the isentropic manner is increased by a maximum of 24 $\%$ than the basic cycle with expansion valve If the velocity nonequilibrium in the mixing process is assumed the COP of the cycle is increased with the increase of the length and the decrease of the section area of the mixing tube. The best cycle performance is obtained when the divergent angle of diffuser is 7.

• 항공우주시스템공학회지
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• 제8권1호
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• pp.18-23
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• 2014

This thesis is simulated a aircraft nose landing gear drop-test. flow rate-to-pressure difference characteristics of damping orifices for a nose landing gear is investigated by CFD analyses. Orifice is kind of poppet valve type. it is simulated pressure drop with variable orifice area. it is simulated landing gear model by using ADAMS with CFD result. It's performance evaluated landing gear drop-test and analyzed the results.

• Journal of Advanced Marine Engineering and Technology
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• 제32권7호
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• pp.1044-1050
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• 2008

Most of developed countries, the consumption of fossil fuels has been serious problems that cause serious environment pollution like acid rain, global warming. Also, we have faced that limitation fossil fuels will be exhausted. Currently, small hydropower attracts attention because of its small, clean, renewable, and abundant energy resources to develop. 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. Tubular-turbine among small hydraulic power generation can be used at low-head. The purpose of this study is to research turbine's efficiency due to runner vane angle using CFD analysis.

• 대한기계학회논문집
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• 제18권4호
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• pp.920-932
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• 1994

The combustion phenomena of a reciprocating engine is one of the most important processes affecting performance and emissions. One effective way to improve the engine combustion is to control the motion of the charge inside a cylinder by means of optimum induction system design, because the flame speed is mainly determined by the turbulence at compression(TDC) process in S.I. engine. It is believed that the tumble and swirl motion generated during intake breaks down into small-scale turbulence in the compression stroke of the cycle. However, the exact nature of their relationship is not well known. This paper describes cycle resolved LDV measurement of turbulent flow inside the cylinder of a 4-valve engine under motoring(non-firing) conditions, and studies the effect of intake port configurations on the turbulence characteristics using following parameters ; Eulerian temporal autocorrelation coefficient, turbulence energy spectral density function, Taylor micro time scale, integral time scale, and integral length scale.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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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%.

• 설비공학논문집
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• 제13권3호
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• pp.153-159
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• 2001

A system simulation program was developed for a multi-type inverter heat pump. Electronic expansion valve(EEV) was used to extend the capacity modulating range of the heat pump as expansion device. The program was also developed to calculate actual system performance with the building load variation with climate during a year. The performance variation of a multi-type hat pump with two EEV and an inverter compressor was simulated with compressor speed, capacity, and flow area of the EEV. As a result, the optimum operating frequency of the compressor and openings of the expansion device were decided at a given load. As compressor speed increased, he capacity of heat pump increased, the capacity of heat pump increased. Therefore flow area of EEV should be adjusted to have wide openness. Thus the coefficient of performance(COP) of the heat pump decreased due to increasement of compressor power input. The maximum COP point at a given load was decided according to the compressor speed. And under the given specific compressor speed and the load, the optimum openings point of EEV was also decided. Although the total load of indoor units was constant, the operating frequency increased as the fraction of load in a room increased. Finally ad the compressor power input increased, the coefficient of performance decreased.

• 항공우주기술
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• 제9권2호
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• pp.63-72
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• 2010

발사체 추진시스템에서 CC(Combustion Chamber) 산화제 개폐밸브는 액체산소를 연소기로 공급 및 차단함으로써 연소를 개시 및 중단시킬 뿐만 아니라, 정상운영 상태에서는 연소기 내 안정된 연소가 가능하도록 일정한 유량의 액체산소를 공급한다. TM(Technology Model)에 비해 높은 유출계수를 가지는 EM(Engineering Model)이 전반적인 요구 성능을 만족하는 것으로 나타났지만, 성능 향상을 위해 EM의 주요 부분에 대한 추가적인 설계 변경을 수행하였다. 공압 제어부, 중간 플랜지, 그리고 밸브 입구의 립 부분의 형태를 설계 변경하였으며, 해당 시험 시제를 제작하여 성능시험을 수행하였다. 이러한 성능 시험을 통해 의도했던 성능 향상이 이루어진 것을 최종 확인하였다.