• International Journal of Air-Conditioning and Refrigeration
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• 제8권2호
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• pp.60-68
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• 2000

An experimental study was peformed to investigate characteristics of an inverter driven heat pump system with a variation of compressor frequency and expansion device. The compressor frequency varied from 30Hz to 75Hz, and the performance of the system ap-plying three different expansion devices such as capillary tube, thermostatic expansion valve(TXV), and electronic expansion valve (EEV) was measured. The load conditions were altered by varying the temperatures of the secondary fluid entering condenser and evaporator with a constant flow rate. When the test condition was deviated from the standard value(rated value), TXV and EEV showed better performance than capillary tube due to optimal control of mass flow rate and superheat. In the present study, it was observed that the variable area expansion device had better performance than constant area expansion device in the inverter heat pump system due to active control of flow area with a change of com-pressor frequency and load conditions.

• 한국전산유체공학회지
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• 제21권4호
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• pp.54-60
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• 2016

The valve used in nuclear power plant must be qualified but the limitation of the test facility leads to use the numerical analysis. The flow coefficient is calculated with the consideration of the pressure, velocity and geometry. And the flow coefficient is the important physical property which is prepared using experiment or analysis by valve manufacturer. In this study, the analysis model was made according to ISA 75.02.01 and the mass flow rate and pressure drop ratio was calculated. The model of the expansion factor was applied to the simulation result and the pressure drop ratio at the start of the choked flow in the valve was found. With the simulation result, the consideration was performed that the expansion factor is the important physical property to the system engineer in addition to the flow coefficient.

• 동력기계공학회지
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• 제18권1호
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• pp.69-75
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• 2014

The pressure and temperature characteristics of mixed refrigerant gases in bulb for thermostatic expansion valve were studied using R22 refrigerant and $N_2$ gases. The characteristics of mixed refrigerant gases were investigated according to pressure variation and the variation of composition ratio of R22 refrigerant and $N_2$ gases in the temperature range of -$15^{\circ}C$~$15^{\circ}C$. The Maximum operating pressure(MOP) of mixed refrigerant gases were showed a tendency to decrease with decreasing the mixing ratio of $N_2$ gas. The characteristics in the case of the mixing ratio of 90:1 for R22 refrigerant and $N_2$ gases were the same result as Reference refrigerant. In addition, the characteristics of the mixed refrigerant gases in the mixing ratio of 90:1 for R22 refrigerant and $N_2$ gases were showed almost linear in the measurement range of pressure-temperature, and the physical properties also were showed similar results with Reference refrigerant. It was able to confirm that a MOP on the thermostatic expansion valve for sensing bulb can be maintained by adjusting the mixing ratio of R22 refrigerant and $N_2$ gases.

• Journal of Chest Surgery
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• 제56권4호
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• pp.255-261
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• 2023

Background: The surgical threshold for bicuspid aortic valve (BAV)-related aortopathy is a matter of debate due to its uncertain etiology and prognosis. This study investigated the prognosis of unrepaired BAV aortopathy in patients undergoing surgical aortic valve replacement (SAVR). Methods: We retrospectively analyzed data from 720 patients (age, 60.8±11.5 years; 246 women) who underwent SAVR for BAV disease without aortic repair between 2005 and 2020 at Asan Medical Center. The clinical endpoints were defined as occurrences of sudden death, aortic dissection or rupture, and elective aortic repair. To estimate postoperative changes in the dimensions of the unrepaired aorta, the individual annual aortic expansion rate was calculated. Multiple linear regression models were used to evaluate the risk of aortic expansion. Results: The mean ascending aortic diameter was 39.5±4.6 mm, and 299 patients (41.5%) had a baseline ascending aorta diameter >40 mm. During 70.0±68.3 months of follow-up, the mean annual aortic expansion rate was 0.39±1.96 mm/yr, no aortic dissection or rupture was observed, and sudden deaths were reported in 12 patients (0.34% per person-year). Linear regression analysis revealed no significant correlation between the baseline ascending aortic diameter and postoperative aortic expansion (R²=0.004, β=-0.84, p=0.082). Conclusion: In selected patients undergoing SAVR for a BAV (<55 mm), the risk of adverse aortic events was very low. As this observation contradicts current practice guidelines advocating for proactive aortic replacement in dilated ascending aortas measuring >45 mm, the study results need further validation by studies involving larger populations or randomized controlled trials.

• 한국구조물진단유지관리공학회 논문집
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• 제28권1호
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• pp.46-52
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• 2024

연약지반에서의 도로 침하 및 지진에 의한 누수 및 수도관의 파열에 따라 배관시스템용 신축이음장치의 구조적 안전성이 강조되고 있다. 일반적으로 배관 시스템의 다양한 손상을 방지하기 위해 신축이음에 금속 벨로우즈 사용하고 있다. 본 연구에서는 밸브실 시스템의 내진 성능을 평가하기 위해 진동대를 이용하여 내진시험을 수행하였다. 밸브실과 강관연결부의 구조적 안전성 평가를 위하여 신축이음(벨로우즈) 및 일반배관을 적용하였으며, 변형률 게이지를 부착하여 지진동에 의한 영향을 분석하였다. 진동대 실험결과, 일반배관이 적용된 경우보다 신축이음(벨로우즈)을 설치한 경우에 밸브실 구조체 및 유입·유출관의 변형율 1/100 및 1/20 수준으로 감소를 확인하였다.

• 한국포장학회지
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• 제24권3호
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• pp.113-120
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• 2018

The one-way gas valve developed in this study was designed to prevent the breakage of packages from increased internal pressure, which is a problem in packaged Kimchi, and simultaneously reduce the outflow of the offodor release. The effect of the one-way gas valve on the headspace atmospheric compositions was investigated in the packaging system. The changes of atmospheric compositions and quality factors of Kimchi, such as $CO_2$ accumulation, pH, titratable acidity, and salinity, were measured during a 4-week storage period at $4^{\circ}C$. The Kimchi package with the one-way gas valve dramatically reduced pressure build-up in the pouch by allowing the controlled flow of gas to the atmosphere. In addition, the package design allows the possibility of controlling the gas generated from Kimchi by adjusting the viscosity of the open pressure control oil. The one-way gas valve did not affect the sensory characteristics of Kimchi products during the storage period. Furthermore, the deodorizing capability of the activated carbon contained in the one-way gas valve effectively reduced the off-odor of Kimchi products released along with carbon dioxide. The novel one-way gas valve is considered to be an active packaging system that can solve major problems of expansion and off-odor leakage in the packaging of Kimchi.

• 한국산업융합학회 논문집
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• 제14권3호
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• pp.113-119
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• 2011

This study analyzed facts affecting the performance of refrigeration systems after throttling actions, by changing the amount of refrigerant according to adjusting the opening of manual expansion valve to 80%, or 20% with vapor compressional refrigeration training equipment. At opening of 20%, the inlet and outlet temperature of compressor, subcooling and superheat, condenser heat, refrigeration effect, flash gas heat, coefficient of performance were higher, while at 80%, condensing pressure, evaporating pressure, compression work were higher, Thus, we could see changes in the amount of refrigerant affect the performance of the refrigeration system.

• 한국수소및신에너지학회논문집
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• 제19권3호
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• pp.182-188
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• 2008

In order to improve scavenging performance of free piston hydrogen fueled engine, this study estimate compatibility of uni-flow scavenging. The scavenging flow characteristics in the cylinder is investigated by flow visualization and PIV method. Consequently it has been found that the scavenging performance decreased with abnormal expansion of piston and delay of the exhaust valve opening timing. And the scavenging performance of exhaust valve located center in cylinder head is better than that of exhaust valve located side in cylinder head.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.279-282
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• 2011

가스 발생기 산화제 개폐 밸브에 사용되는 벨로우즈의 구조 해석 및 시험이 수행되었다. 해석은 상온 및 극저온에서 EJMA (Expansion Joint Manufacturing Association) 표준 및 상용 유한 요소 해석프로그램인 Abaqus v6.9를 이용하여 수행되었다. 스프링 강성, 응력 및 피로 수명 해석 결과들이 비교되었고 유한 요소 해석 결과에서 접촉 및 재질의 소성에 의한 영향을 살펴보았다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1491-1496
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• 2009

Fluid flow and structural analyses of an electronic expansion valve (EEV) using CO2 as a working refrigerant are carried out to estimate the mass flow rate and maximum stress. An engineering sample EEV that the orifice diameter is 1.8 mm was fabricated. The mass flow rates were measured at various EEV inlet temperatures and pressures for several EEV openings using experimental heat pump system. The sample EEV has over 35 MPa burst pressure and the maximum mass flow rate of CO2 through the EEV increased to 100 g/s at full opening condition.