• 한국수소및신에너지학회논문집
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• 제25권3호
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• pp.297-304
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• 2014

The purpose of this study is to evaluate the experimental performance characteristics of a water-to-water geothermal heat pump featuring a vapor refrigerant injection for the production of hot water. The performance of geothermal heat pump with a vapor injection was evaluated by comparing with that of a conventional geothermal heat pump without a vapor injection. For heating operation, the geothermal heat pump with a vapor injection is superior in COP and heating capacity. The vapor injection was more effective for supplying hot water while overloading. The vapor injection was effective for the improvement of the cooling capacity. However, the vapor injection was not effective for the increasing of COP according to the increased input of a compressor. The advantage of vapor injection in water-to-water geothermal heat pump become disappeared while cooling operation with lower part loading.

• 동력기계공학회지
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• 제14권3호
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• pp.25-32
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• 2010

전 세계적으로 급속도로 인기가 더해가고 있는 수소에너지는 높은 전환 효율성, 재생성, 친환경적인 특징을 가지며 미래의 주 에너지가 될 것이다. 왕복동식 압축기를 통과한 후의 수소 가스의 압력은 높은 맥동압을 가진다. 스너버는 압축기의 한 구성품으로 맥동압을 낮추고 수소가스의 불순물을 제거하기 위해 사용된다. 이 연구에서의 실험은 스너버 시스템에 사용된 강관의 맥동에 관해 조사하기 위해서 수행되었다. 맥동압은 12 Hz ~ 60 Hz의 모터속도에서 RMS값을 기준으로 0.1625% ~ 0.5305% 그리고 평균압력을 기준으로 0.1621% ~ 0.5277% 감소하였다. 압력손실은 RMS값을 기준으로 0.1092% ~ 1.4419%, 평균압력을 기준으로 0.1493% ~ 1.7507%로 측정되었다. CFD를 이용한 수치해석값은 실험값이 거의 비슷한 결과를 나타내고 강관 관로 내부 가스의 자세한 압력을 설명하기 위한 중요한 역할을 수행한다.

• 한국수소및신에너지학회논문집
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• 제28권5호
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• pp.570-576
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• 2017

Gas turbine system with steam injection has shown outstanding advantages such as high specific power and NOx reduction. In the present work, a comparative exergetic analysis was carried out for Steam Injected Gas Turbine (STIG), Regenerative Steam Injected Gas Turbine (RSTIG), and Regenerative After Fogging Gas Turbine (RAF). Effects of pressure ratio, steam injection ratio and steam injection method on the system performance was theoretically investigated. The results showed that the order of the highest exergy efficiency is RSTIG, RAF, and STIG for low pressure ratios but STIG, RSTIG, and RAF for high pressure ratios. In each arrangement, the combustion chamber has the highest exergy destruction and the compressor has the second one.

• 한국수소및신에너지학회논문집
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• 제20권6호
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• pp.526-533
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• 2009

In this paper, cycle performance analysis of $CO_2-C_3H_8$ (R744-R290) cascade refrigeration system with internal heat exchanger is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree and gas cooling pressure and evaporating temperature in the propane (R290) low temperature cycle and the carbon dioxide (R744) high temperature cycle. The main results were summarized as follows : The COP of cascade refrigeration system of $CO_2-C_3H_8$ (R744-R290) increases with the increasing subcooling degree, but decreases with the increasing superheating degree. The COP of cascade refrigeration system increases with the increasing evaporating temperature, but decreases with the increasing gas cooling pressure. Therefore, superheating and subcooling degree, compressor efficiency, evaporating temperature and gas cooling pressure of $CO_2-C_3H_8$ (R744-R290) cascade refrigeration system have an effect on the COP of this system.

• 한국수소및신에너지학회논문집
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• 제27권5호
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• pp.571-580
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• 2016

In this paper, performance of the gas turbine combined cycle(GTCC) using pre-combustion carbon capture technology was comparatively analysed. Steam reforming and autothermal reforming were used. In the latter, two different methods were adopted to supply oxygen for the reforming process. One is to extract air form gas turbine compressor (air blowing) and the other is to supply oxygen directly from air separation unit ($O_2$ blowing). To separate $CO_2$ from the reformed gas, the chemical absorption system using MEA solution was used. The net cycle efficiency of the system adopting $O_2$ blown autothermal reforming was higher than the other two systems. The system using air blown autothermal reforming exhibited the largest net cycle power output. In addition to the performance analysis, the influence of fuel reforming and carbon capture on the operating condition of the gas turbine and the necessity of turbine re-design were investigated.

• 한국가시화정보학회지
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• 제17권1호
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• pp.85-92
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• 2019

Numerical visualization is conducted to confirm the variation of flow characteristics and pressure drop by the shape of channels on the cathode flow path in hydrogen fuel cells for unmanned aerial vehicles(UAVs). Generally, a light-weight fan is commonly used rather than a heavy air compressor at UAVS. However, in case of blower fan, a large pressure drop in the flow path causes the blocking of the oxygen supply to the fuel cell. Therefore, the uniformity of flow inside the cathode has to be achieved by changing the shape of the cathode. The flow channel, the duct shape, and the diameter of the fan are changed to optimize the flow path. As a result, it is confirmed that the optimal flow path can decrease the velocity difference between the center and outer flow by 1.8%. However, It should be noted that the channel size can increase the pressure drop.

• 한국수소및신에너지학회논문집
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• 제30권4호
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• pp.369-375
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• 2019

Air conditioners adopting high energy efficiency and low global warming potential (GWP) refrigerant are being developed globally. In case of commercial air conditioner, R32 with lower GWP than R410A is attracting industrial attentions. In this study, the performance of water-to-water geothermal heat pump adopting R32 is compared with that of the heat pump using R410A. By using R32 instead of R410A, heating capacity and COP in heating standard condition can be increased by 8.8% and 6.3% respectively. Also, cooling capacity and COP in cooling standard condition can be increased by 5.3% and 3.1% respectively by using R32. But in case of using R32, systemic improvements are required to decrease discharge temperature of compressor since discharge temperature rises abnormally in heating operations.

• 한국수소및신에너지학회논문집
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• 제30권3호
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• pp.276-281
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• 2019

The process of separating oxygen and nitrogen from the air is mainly performed by electric liquefaction, which consumes a lot of electricity, resulting in higher operating costs. On the other hand, when used for cold energy of LNG, electric power can be reduced compared to the electric Linde cycle. Currently, LNG cold energy is used in the cold refrigeration warehouse, separation of air-liquefaction, and LNG cold energy generation in Japan. In this study, the system using LNG cold energy and the Linde cycle process system were simulated by PRO/II simulators, respectively, to cool the elevated air temperature from the compressor to about $-183^{\circ}C$ in the air liquefaction separation process. The required amount of electricity was compared with the latent heat utilization fraction of LNG, the LNG supply pressure, and the LNG cold energy usage. At the air flow rate of $17,600m^3/h$, the power source unit of the Linde cycle system was $0.77kWh/m^3$, compared with $0.3kWh/m^3$.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.109-114
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• 2008

This paper presents the development status of a subscale precooled turbojet engine "S-engine" for the hypersonic cruiser and space place. S-engine employs the precooled-cycle using liquid hydrogen as fuel and coolant. It has $23cm{\times}23cm$ of rectangular cross section, 2.6 m of the overall length and about 100 kg of the target weight employing composite materials for a variable-geometry rectangular air-intake and nozzle. The design thrust and specific impulse at sea-level-static(SLS) are 1.2 kN and 2,000 sec respectively. After the system design and component tests, a prototype engine made of metal was manufactured and provided for the system firing test using gaseous hydrogen in March 2007. The core engine performance could be verified in this test. The second firing test using liquid hydrogen was conducted in October 2007. The engine, fuel supplying system and control system for the next flight test were used in this test. We verified the engine start-up sequence, compressor-turbine matching and performance of system and components. A flight test of S-engine is to be conducted by the Balloon-based Operation Vehicle(BOV) at Taiki town in Hokkaido in October 2008. The vehicle is about 5 m in length, 0.55 m in diameter and 500 kg in weight. The vehicle is dropped from an altitude of 40 km by a high-altitude observation balloon. After 40 second free-fall, the vehicle pulls up and S-engine operates for 60 seconds up to Mach 2. High altitude tests of the engine components corresponding to the BOV flight condition are also conducted.

• Tribology and Lubricants
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• 제37권3호
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• pp.91-98
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• 2021

This paper presents a hydrostatic bearing design and rotordynamic analysis of a turbo expander for a hydrogen liquefaction plant. Th~e turbo expander includes the turbine and compressor wheel assembled to a shaft supported by two hydrostatic radial and thrust bearings. The rated speed is 75,000 rpm and the rated power is 6 kW. For the bearing operation, we use pressurized air at 8.5 bar as the lubricant that is supplied to the bearing through the orifice restrictor. We calculate the bearing stiffness and flow rate for various gauge pressure ratios and select the orifice diameter providing the maximum bearing stiffness. Additionally, we conduct a rotordynamic analysis based on the calculated bearing stiffness and damping considering design parameters of the turbo expander. The predicted Cambell diagram indicates that there are two critical speeds under the rated speed and there exists a sufficient separation margin for the rated speed. In addition, the predicted rotor vibration is under 1 ㎛ at the rated speed. We conduct the operating test of the turbo expander in the test rig. For the operation, we supply pressurized air to the turbine and monitor the shaft vibration during the test. The test results show that there are two critical speeds under the rated speed, and the shaft vibration is controlled under 2.5 ㎛.