• 한국초전도ㆍ저온공학회논문지
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• 제14권3호
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• pp.1-4
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• 2012

Effects of artificial holes on the cooling efficiency of single grain YBCO bulk superconductors were studied. Single grain YBCO bulk superconductors without artificial holes, with six 2.4 mm holes and six holes filled with Bi-Pb-Cd-Sn metal solder were fabricated by a top-seeded melt growth process for powder compacts with/without holes. Simulation for the cooling rate to a liquid nitrogen temperature (77 K) of YBCO samples was carried out using a finite element method (FEM) and the results are compared with the actual cooling rates of samples in liquid nitrogen. The simulated cooling times for the YBCO sample without holes, with six holes and with six holes filled with the metal solder were 80, 47 and 75 sec. respectively, which are similar to the actual cooling times of 84, 52 and 78 sec. estimated for the same samples cooled in liquid nitrogen. The shorter cooling time of the sample with artificial holes are attributed to the increased surface areas associated with the presence of artificial holes. The metal filling into the holes did not give any remarkable effect on the cooling efficiency.

• 설비공학논문집
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• 제18권1호
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• pp.81-86
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• 2006

High temperature superconducting (HTS) power cable requires forced sub-cooled LN2 flow cooling. Liquid nitrogen is circulated by a pump and cooled back by cooling system. Typical operating temperature range is expected to be between 65 K and 77 K. The HTS power cable needs sufficient cooling to overcome its low temperature heat load. For successful cooling, the hydraulic characteristics of the HTS power cable must be well investigated to design the cables. Especially, the pressure drop in the cable is an important design parameter, because the pressure drop decides the length of the cable, size of the coolant circulation pump and circulation pressure, etc. This paper describes measurement and investigation of the pressure drop of the cooling system. In order to reduce the total pressure drop of the cooling system, the flow rate of liquid nitrogen must be controlled by rotational speed of the circulation pump.

• 한국세라믹학회지
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• 제43권7호
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• pp.433-438
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• 2006

In order to examine the working condition of melts in tin bath of float process it was investigated Sn diffusion behavior and solidification rate of melts for alkali-alkaline earth-silica PDP substrate glasses such as commercial CaO rich CS-77 glass, commercial $Al_2O_3$ rich PD-200 glass and self developed $SiO_2$ rich T-series (T-2, T-4, T-6) glasses. In the case of Sn depth and concentration created in glass surface by ion exchange between Sn and alkali, T-series showed lower value than CS-77, especially T-2 is more excellent than PD-200. The solidification rate of melts expressed by cooling time between $log{\eta}=4\;and\;7.6dPa{\cdot}s$ was low for T-series comparing with CS-77 and PD-200. Therefore, it was concluded that T-series is desirable considering forming condition in the tin bath of the float process.

• 한국초전도ㆍ저온공학회논문지
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• 제22권4호
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• pp.40-44
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• 2020

This paper describes the real operation of 2 kW class reverse-Brayton refrigeration system with neon as a working fluid. The refrigeration cycle is designed with operating pressure of 0.5 and 1.0 MPa at low and high pressure side, respectively. Compressor package consists of several helium scroll compressors witch are originally used for driving GM cryocooler. Three segments of plate heat exchanger are adopted to cover the wide temperature range and the refrigeration power is produced by turbo expander. The developed refrigeration system is successfully operated at its target temperature of 77 K. In experiments, all parameters such as pressure, temperature, mass flow rate and valve opening are measured to investigate characteristics during cool-down process and normal state. The difference between design and real operation is discussed with measured experimental data. At normal state of 77 K operation, the developed reverse-Brayton refrigeration system shows 1.83 kW at 68.2 K of cold-end temperature.

• 한국안전학회지
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• 제18권4호
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• pp.71-77
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• 2003

To inject fresh air into a fire room, Positive Pressure Ventilation (PPV) can be used and the blower of PPV increases inside pressure of the room. It makes high flow rate of products of combustion, smoke and heat from the structure, and it is very helpful to fireman on the fire extinguishing work. The flame moves to the direction of airflow and the temperature of flame can be decreased rapidly. In this experiment, a water mist system is applied to PPV to increase the effectiveness, and various effective factors are studied. n-Heptane and pine wood stick were used as fuel. Temperatures at the above and behind the combustion pan were strongly reduced by the water mist system and by the convective cooling with airflow. The smoke density was also decreased by PPV with water mist system and it can be explained by the absorption of smoke particles on the water mist droplet and by the strong exhausting effects of mobile fan.

• 한국초전도ㆍ저온공학회논문지
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• 제5권1호
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• pp.133-135
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• 2003

Cryogenic systems are requirement for the operation of HTS power cables. In general, HTS power cables require temperature below 77K, a temperature that can be achieved from the liquid nitrogen at latm or sub-cooled LN2 above latm. HTS power cable needs sufficient refrigeration to overcome its low temperature heat loading. This loading typically cones in two forms : (1) heat leaks from the surroundings and (2) internal heat generation. This paper explains the cooling test system of 10m HTS power cable. This system is composed of storage dewar, auto fill system, core cryostat and cold-box. Storage dewar is a LN2 storage tank and auto fill system is a LN2 supply device to the sub-cooler, Core cryostat is a LN2 flow line. Cold box is a control unit of temperature and flow rate. It is composed of control valve, flow meter, sub-cooler and circulation pump, etc..

• 한국수정란이식학회지
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• 제29권3호
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• pp.241-248
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• 2014

본 연구에서 생쥐 초기 배아를 이용하여 동결 보존된 배아의 생존율 또는 발달율에 영향을 미치는 요인들의 상관관계를 알아본 결과, 배아의 발달 단계에 따른 동결 - 해동 후 생존율에 있어서는 2세포기 배아가 4~8세포기 배아보다 유의하게 높았으나(p<0.01), 배 발달율에 있어서는 4~8세포기 배아가 유의하게(p<0.01), 높아 생존율과 배 발달율과는 상관관계가 없는 것으로 사료된다. 또한, 동결 보호제에 따른 배아의 생존율에 있어서는 2, 4~8세포기 배아 모두 DMSO에서 유의하게 높았으나(p<0.01), 배 발달율에 있어서는 EG가 DMSO에 비해 더 유의하게 높은 성적을 나타내어(p<0.01, p<0.05) 동해로 인한 상해가 적은 것으로 생각되어 2, 4~8세포기 배아에서 EG가 더 효과적인 동결 보호제로 사료되며, 동결 프로그램으로는 완만 동결 - 급속 해동법이 더 우수한 프로그램으로 보인다.

• 한국게임학회 논문지
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• 제12권1호
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• pp.67-77
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• 2012

최근 체감형 인터페이스 기술이 발달하면서 체력 향상을 위한 운동게임에 대한 관심이 높아 지고 있다. 우리는 이러한 기능성 게임이 단지 스포츠 행위의 동작 인식뿐만 아니라 특정 운동 효과를 보장해야 한다고 생각한다. 본 논문은 이러한 기능성 운동게임이 심박수와 선호도에 어떠한 영향을 미치는지 연구할 것이다. 우리는 유산소 운동을 위해 개발한 운동게임인 GalaxyBike를 이용하여 실험을 하였다. 또한, 무선 심박센서를 이용하여 피험자들의 심박수를 준비운동, 본운동, 그리고 마무리 운동단계에서 측정하였다. 게임을 완료한 후에는, 설문지를 이용하여 선호도를 조사하였다. 우리는 게임과 운동을 동시에 수행하는 기능성 운동 게임이 건강 체력향상에 대한 참여 유발과 심박수를 증가시키며 유산소 운동의 효과를 제공하는 것을 확인하였다.

• 수산해양기술연구
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• 제32권1호
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• pp.67-77
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• 1996

The heat transfer performance of R - 11 vapor condensing on integral fin tubes has been studied using fin tubes having the fin density from 748 to 1654 fins per meter. Electric heater supplied heat energy to the boiler to generate R - 11 vapor over the range of 25-60W. Condensation rates of each tubes were tested under the condition of cooling water flow rate from 400l/h to 2500l/h. For the seven fin tubes tested, the best performance has been obtained with a tube having a fin density of 1417fpm and a fin height of 1.3mm. This tube has yielded a maximum value of the heat transfer coefficient of 16500W/$m_2$K, at a vapor to wall temperature difference of 3K. Experimental results of integral fin tubes have been compared with available predictive models such as Beatty - Katz's analysis, Webb's analysis, Sukhatme's analysis and Rudy's empirical relation. The experimental results were shown to be in good agreement with that of the Sukhatme's analysis.

• Progress in Superconductivity
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• 제3권1호
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• pp.99-103
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• 2001

We have conducted two runs of interlaboratory comparison on Ag-sheathed Bi-2223 tapes to evaluate the level of measurement techniques for the critical current measurement. Two classes of specimens were prepared for parallel and serial routings and sent to four participating laboratories. The critical currents of specimens were measured at 77 K in zero magnetic field. In the first comparison, we used twenty different Bi-2223 tapes as specimens for comparison and participating laboratories measured the specimens using their own instruments and procedures. As a result, the scattering of data on the first comparison showed -3.0% to +l2.2% for the parallel routing and -0.7% to +l5.1% for the serial routing. Major sources of these variations were attributed to different measurement techniques. Thus, the second comparison of measurement was done on the same specimens under specified measurement conditions, particularly in terms of cooling procedure and sweep rate of the test current. The variations for the second comparison were decreased -3.1% to +3.2% far the parallel routing and -1.8% to +7.7% fur the serial routing.