• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.2194-2199
• /
• 2007

An experimental study is performed to investigate the thermal and flow characteristics of subcooled liquid nitrogen in a natural circulation loop. Experimental apparatus is designed and constructed such that a closed loop is cooled at the top by a cryocooler and heated nearly at the bottom by cartridge heaters. Steady state is obtained by controlling the heating power to the cartridge heaters and a thin-film heater to reduce the cooling power of the cryocooler. Temperature is measured at several locations of the loop and the mass flow rate through the loop is estimated from the energy balance in terms of the measured temperatures. Experiment is repeated for various values of the vertical height between the cooling and heating parts. The results show that the heat transfer capability of the loop has a maximum at a certain value of height. The optimal height to maximize the heat transfer is in a good agreement with analytical prediction to take into account the buoyancy and viscous forces in the loop.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집D
• /
• pp.950-954
• /
• 2001

Gasoline engine manufacturers are currently considering designs that will result in low combustion air temperature for improvement of fuel consumption and emission levels. There are a variety of cooling systems that can be used to accomplish this goal. Coolong is therefore normally achieved through a balance of ram and fan action. This paper studies the various systems and compare the cooling performance for several conditions, based on a automotive engine. An experimental analysis was developed to predict the interaction of the fan system and the heat exchangers of the engine cooling system. The local temperature induced by the fan on the cooling system is measured. These experimental result were accomplished using air flow management techniques.

• 태양에너지
• /
• 제9권3호
• /
• pp.3-12
• /
• 1989

Semi-greenhouse type solar-dehumidification drying of oak was carried out to investigate the possibility to dry wood using solar energy in Korea. The energy balance equation was set up, considering all the energy requirements, and the solar radiation was calculated to analyze the efficiencies of solar dryer with and without the dehumidifier. The average temperature inside dryer and collector rose up to $52^{\circ}C$ and $70^{\circ}C$, respectively. The average daily total beam, diffuse, and ground-reflected radiations were 7.27MJ, 8.70MJ, and 0.33MJ on the roof and 2.08MJ, 4.84MJ, and 5.37MJ on the south wall collector, respectively. Heat efficiency of solar dryer was 14.04% with dehumidifier and 13.13% without dehumidifier. The energy required to remove 1g of water from wood was 0.0289MJ/g in solar-dehumidification drying and 0.0310 MJ/g in semi-greenhouse type solar drying.

• Journal of Electrical Engineering and Technology
• /
• 제2권3호
• /
• pp.366-372
• /
• 2007

Joining thin aluminum alloy is difficult using most welding techniques. Many of the problems are associated with bum-through by the high heat input. Common welding techniques are TIG (Tungsten Inert Gas), MIG (Metal Inert Gas), and PULSE-MIG welding. The method provides more control of the heat balance in the welding arc by taking advantage of the different arc characteristics obtained with each of the two polarities. In this paper, we proposed a new welding method by control DSP 320C32, and the characteristic and experiment result-voltage, current, welding bead, and penetrations by this method are presented.

• 한국연소학회지
• /
• 제20권2호
• /
• pp.1-13
• /
• 2015

Drying, which is the oldest and most energy-intensive process, is an essential process for treatment of solid product. The specific procedure to design and evaluate the dryers, which are a rotary kiln dryer and a flash dryer, in case of drying the high-moisture coal was described. From determination of size to the heat and mass balance in one-dimensional model were conducted to evaluate the performance of dryers. Heat consumption, inlet gas temperature and size of the dryers were compared between a rotary kiln dryer and a flash dryer. Further considerations to evaluate the reactor elaborately were also discussed. Performance simulation of dryers along with the design procedure described here will provide helpful basis for understanding the concept of reactor design.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
• /
• pp.369-372
• /
• 1999

Using Ag sheathed multi filamentary Bi-2223 tape, stability against heat pulse has been investigated. The measured normal zone propagation(NZP) velocity of the tape was found to be faster due to increase of operating current and magnetic field, and agree well with calculated data from one dimensional heat balance equation. Minimum quench energy(MQE) was found to be larger than 17 J at 30 K zero magnetic filed at operating current of 96.5 with respect to I$_c$.

• 한국초전도저온공학회:학술대회논문집
• /
• 한국초전도저온공학회 2001년도 학술대회 논문집
• /
• pp.92-94
• /
• 2001

We investigated quench recovery characteristics of Au/YBCO thin film meander lines. YB$a_{2}$$Cu_{3}$ $O_{7}$films were coated in-situ with a gold layer and patterned into 2 mm wide meander lines by photolithography. The limiters were tested with simulated fault currents at various source voltages. Resistance decreased first slowly and then rapidly to zero. Resistance vs. time curves for different source voltages fell on top of each other when translated horizontally. The slowly varying portion of data fell on straight lines of a slope on a semi-log scale at all source voltages. A heat balance equation reflecting heat loss from meander lines to surroundings explains these results quantitatively.

• 한국해양공학회지
• /
• 제9권1호
• /
• pp.151-160
• /
• 1995

The characteristics of low temperature impact toughness and stress corrosion resistance at boiling MgCl$_2$ solution of GTA and SMA weld of duplex stainless steels have been investigated. The impact toughness was highest at the GTAW weld metal and lowest at the SMAW weld, which was almost the same as that of the SMAW heat-affected zone. This was attributable to influence of austenite-ferrite phase balance, and the degree and nature of precipitation that occurred during welding. The SCC resistance of the weldments was slightly higher than that of the base metal, whereas no difference in the SCC resistance was found between two different weldments.

• 대한기계학회논문집
• /
• 제8권6호
• /
• pp.553-563
• /
• 1984

본 연구에서는 선정한 난방모델에 대하여 열회로망을 만들어 각 구성성분에 대하여 에너지평형식을 세워 시뮬레이션 모델을 구하고 여기에 경계조건과 초기조건을 대입하여 수치해석으로 푼 결과를 실측치와 비교하였다. 또한 축열벽의 열용량변화, 통기구의 개폐, 통기구에 자동온도조절 홴(fan)의 설치, 야간단열의 설치 및 온실크기 의 변화 등이 온방온도에 미치는 영향을 규명하였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집B
• /
• pp.940-945
• /
• 2001

Gasoline engine manufacturers are currently considering designs that will result in low combustion air temperature for improvement of fuel consumption and emission levels. There are a variety of cooling systems that can be used to accomplish this goal. Cooling is therefore normally achieved through a balance of ram and fan action. This paper studies the various systems and compare the cooling performance for several conditions, based on a automotive engine. An experimental analysis was developed to predict the interaction of the fan system and the heat exchangers of the engine cooling system. The local temperature induced by the fan on the cooling system is measured. These experimental result were accomplished using airflow management techniques.