• 공업화학
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• 제33권1호
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• pp.96-102
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• 2022

고분자전해질막 연료전지의 반응물인 수소와 산소는 기체 상태이므로, 반응물이 원활히 전달될수록 작동 전압의 손실을 줄일 수 있다. 높은 전류밀도 영역에서 산소 물질 전달이 전압 손실을 좌우하므로, 환원극 유로의 형상 변경에 대한 연구들이 진행되어 왔다. 환원극 유로 형상 중에서 유로를 막는 블록은 반응물을 다공성 매질인 기체확산층으로 강제 대류 하도록 사용되었다. 본 연구에서는 간단한 단 채널의 연료전지 모델에 블록을 배치하였다. 전산 유체역학을 사용하였고, 공기 공급 유량을 달리하였을 때 블록으로 인한 강제 대류 효과가 전압-전류 곡선과 국부 전류 밀도에 대한 영향을 연구하였다. 기체확산층으로의 강제 대류 현상을 통하여 적은 공기 공급 유량으로도 높은 전류 밀도를 얻을 수 있었다. 다수의 블록을 직렬로 배치한 경우에 1개의 블록만 배치한 것보다 강제 대류 효과를 증가시켜 높은 전류밀도를 얻을 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.421-426
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• 2005

For the air-conditioner, refrigerant induced noise and vibration should be the problem when it reduced airflow rate in order to reduce the noise at low mode. With the test, it could be verified that one of the main reason for refrigerant induced noise were the velocity and flowing induced force of the refrigerant at the inlet of evaporator. So in order to reduce this velocity with same mass flow rate of refrigerant, quality at the evaporator inlet should be minimized. And in order to reduce flowing induced force of the refrigerant, flowing direction change should be eliminated. So in this paper, it would like to review the characteristics of refrigerating cycle at first and find how the quality and flowing induced force can be minimized.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.237-243
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• 2002

A centrifugal compressor of 50HP for reverse brayton cryocooler using neon as a coolent has been developed. It has relatively low total-to-total pressure ratio but mass flow rate is very small and the voting gas, neon, has greater specific heat ratio than air. It was essential to have very high rotational speed of 100,000 RPM. The efficiency of compressor has great effects on overall system and the COP of cryocooler. To meet the design requirement of the compressor efficiency and to minimized the required rotational speed, highly efficiency impeller having low specific speed was designed. To maintain the overall system efficient high, gas bearing of bump type and high speed permanent magnet synchronus motor was developed and adopted. In this paper, design and performance prediction results of the compressor impeller is presented.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.641-644
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• 2006

Considering properties of the low-heat concrete mixed with the blended cements, the influences compared blended cements with ordinary portland cement made experiments on. (1) Blended cements were superior to OPC in the fresh concrete flow that the use of blended cements reduced chemical admixture. (2) The more the use of additive increase, the more bleeding happens. So it is considered to heights, order, and rate of placement, curing methods and so on. (3) The use of blended cements increase long term strength after 28 days, but decrease early strength and durability. So it is considered to the curing methods and early frost damage, and endurance limit.

• 한국수소및신에너지학회논문집
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• 제19권3호
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• pp.232-238
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• 2008

Research has been proceeded on fuel cell which is fueled by hydrogen. Polymer electrolyte membrane fuel cell (PEMFC) is promising power source due to high power density, simple construction and operation at low temperature. But it has problems such as high cost, temperature dependent performance. These problems could be solved by experiment which is useful for analysis and optimization of fuel cell performance and heat management. In this paper, when hydrogen flows constantly at the stoichiometry of ${\xi}=1.6$, the performance of the fuel cell stack was increased and the voltage difference between each cells was decreased according to the increase of air stoichiometry by 2.0, 2.5, 3.0. Therefore, the control of air flow rate in the same gas channel is important to get higher performance. Purpose of this research is to expect operation temperature, flow rate, performance and mass transportation through experiment and to help actual manufacture of PEM fuel cell stack.

• International Journal of Air-Conditioning and Refrigeration
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• 제6권
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• pp.36-44
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• 1998

R-410a and R-407c which have the best potential among R-22 alternatives were tested as drop-in refrigerants against a set of R-22 baseline tests. The performance evaluations were carried out in a psychometric calorimeter test facility using the residential spilt type air conditioner under the ARI rating conditions. Except the lubricant and hand-operated expansion valve, the other parts of the air conditioner were the same with the commercial system. Performance characteristics were measured; compressor power, capacity, VCR, mass flow rate and COP. The tests showed that R-407c can be directly charged into the current refrigeration system because its vapor pressure and other thermochemical properties are similar to those of R-22. However, it is required to change the volume flow rate of compressor in order to achieve the volumetric capacity of R-22. This results from its relatively small VCR and capacity. Meanwhile, R-410a has vapor pressure values too high to be substituted for the current system and this resulted relatively low COP of R-410a compared to that of R-22.

• 설비공학논문집
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• 제9권1호
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• pp.82-91
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• 1997

R-410a and R-407c witch have the best potential among the substances being considered as R-22 alternatives were tested as "drop in" refrigerants against a set R-22 baseline tests for comparison. The performance evaluations were carried out in a psychrometric calorimeter test facility using the residential split-type air conditioner under the ARI rating conditions. Other than the use of different lubricant and a hand-operated expansion valve, one of the commercial systems was selected for the experiment. Performance characteristics were measured; compressor power, capacity, VCR, mass flow rate and COP. The tests showed that R-407c can be directly applied to the existing refrigeration system because of its similar vapor pressure and other thermopysical properties with those of R-22. However, it required change to the volume flow rate of compressor in order to achieve the similar performance with R-22 because of its relatively small VCR and capacity. Meanwhile, R-410a has too high a vapor pressure to be applied to the existing system and this feature results in relatively low COP of the system compared to that of R-22. But this could be improved by changing compressor design considering R-410a's relatively high VCR and capacity compared to those of R-22.

• 한국진공학회지
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• 제16권6호
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• pp.468-473
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• 2007

본 논문에서는 저압환경에서 실시간으로 나노입자를 측정할 수 있는 PBMS(Particle Beam Mass Spectrometer)의 개발에 대해 서술하였다. 개발된 PBMS의 교정을 위해 NaCl입자를 사용하였다. DMA(Differential Mobility Analyzer)를 통해 +1가로 하전된입자를 1 lpm 발생시켜 그 중 0.086 lpm을 PBMS 입구의 오리피스를 통해 분기하여 유입시켰다. DMA와 PBMS의 전류값을 비교하여 전송효율을 측정한 결과 입자의 크기에 따라 약 50$\sim$60%를 나타내었다. 또한 DMA에서 특정한 크기의 입자를 발생시켜 PBMS로 측정하였으며 그 결과는 입자크기별 농도분포와 잘 일치함을 확인할 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3068-3073
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• 2007

Aerodynamic forces and moments have been used to control rocket propelled vehicles. If control is required at very low speed, Those systems only provide a limited capability because aerodynamic control force is proportional to the air density and low dynamic pressure. But thrust vector control(TVC) can overcome the disadvantages. TVC is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. In this paper, the conceptual design and the performance study on the tapered ramp tabs of the thurst vector control has been carried out using the supersonic cold flow system and shadow graph. Numerical simulation was also performed to study flow characteristics and interactions between ramp tabs. This paper provides to analyze the location of normal shock wave and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• 대한물리의학회지
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• 제18권1호
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• pp.15-24
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• 2023

PURPOSE: This study examined the effects of lowintensity resistance exercise combined with blood flow restriction on muscle activity and muscle fatigue to determine if such a combination may be an alternative to high-intensity resistance exercise in maintaining the muscle mass and strength and preventing degenerative loss of skeletal muscle and to provide basic data for presenting the effectiveness of exercise. METHODS: The interventions were provided for five weeks, four sessions a week, once a day, 60 minutes a session to Experimental group I (n = 13), in which low-intensity resistance exercise was applied by combining blood flow restriction with the biceps curl and experimental group II (n = 12), in which only high-intensity resistance exercise was applied. As a pre-test, the biceps brachii muscle activity and fatigue were measured by surface electromyography, and the hemodynamic variables, such as blood pressure and heart rate, were measured. The post-test was performed identically to the pre-test and compared and analyzed with the pre-test. RESULTS: A significant difference within-group was observed in the biceps brachii muscle activity and fatigue in experimental group I and only in biceps brachii activity in experimental group II. No significant differences were observed between the two groups. CONCLUSION: Since the low-intensity resistance exercise combined with blood flow restriction has similar effects to high-intensity resistance exercise, it is considered an alternative for improving muscle function in groups unable to perform high-intensity resistance exercise.