• Transactions of the Korean hydrogen and new energy society
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• v.35 no.3
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• pp.290-299
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• 2024

In this study, a theoretical study was conducted on the pre-cooling temperature of hydrogen gas and the heat exchanger area in a small-scale liquefied hydrogen system. The small-scale liquefaction system was built and liquid hydrogen production experiments were performed. In this process, the temperature of precooled hydrogen gas was measure to be about 120 K, and then the possibility of a cause was analyzed through pressure analysis of hydrogen gas and container, and analysis of the amount of liquid hydrogen produced. It was found that some reasonable results were obtained from the theoretical approaches. Based on this theoretical approach, we aim to improve the production of liquid hydrogen by optimizing the heat exchange area according to flow rate.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.4
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• pp.247-251
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• 2017

Titanium alloy has been widely used in the aerospace industry because of its high strength and good corrosion resistance. During cutting, the low thermal conductivity and high chemical reactivity of titanium generate a high cutting temperature and accelerates tool wear. To improve cutting tool life, cryogenic machining by using a liquid nitrogen (LN2) jet is suggested. In cryogenic jet cooling, evaporation of LN2 in the tank and transfer tube could cause pressure fluctuation and change the cooling rate. In this work, cooling uniformity is investigated in terms of liquid nitrogen jet pressure in cryogenic jet cooling during titanium alloy turning. Fluctuation of jet spraying pressure causes tool temperature to fluctuate. It is possible to suppress the fluctuation of the jet pressure and improve cooling by using a phase separator. Measuring tool temperature shows that consistent LN2 jet pressure improves cryogenic cooling uniformity.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.170-173
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• 2007

Cooling characteristics of a liner were investigated by a film cooling method using a gas nitrogen in a rocket engine. High temperature gas of this test was made by mixing liquid nitrogen with combustion gas of a liquid rocket. A supply system of gas nitrogen was additionally constructed to the existing test facility of liquid rocket engine, and a new test section consisted of a liner and a gas injection ring was manufactured. A 10 second firing test for finding cooling characteristics of the liner was successfully conducted and liner surface temperatures and hot gas temperature was obtained.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.561-562
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• 2011

• Progress in Superconductivity and Cryogenics
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• v.17 no.3
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• pp.57-61
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• 2015

A Superconducting Fault Current Limiter is an electric power device which limits the fault current immediately in a power grid. The SFCL must be cooled to below the critical temperature of high temperature superconductor modules. In general, they are submerged in sub-cooled liquid nitrogen for their stable thermal characteristics. To cool and maintain the target temperature and pressure of the sub-cooled liquid nitrogen, the cryogenic cooling system should be designed well with a cryocooler and coolant circulation devices. The pressure of the cryostat for the SFCL should be pressurized to suppress the generation of nitrogen bubbles in quench mode of the SFCL. In this study, we tested the performance of the cooling system for the prototype 154 kV SFCL, which consist of a Stirling cryocooler, a subcooling cryostat, a pressure builder and a main cryostat for the SFCL module, to verify the design of the cooling system and the electric performance of the SFCL. The normal operation condition of the main cryostat is 71 K and 500 kPa. This paper presents tests results of the overall cooling system.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.2
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• pp.73-78
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• 2016

An increase in the transistor density of integrated circuit devices leads to a very high increase in heat dissipation density, which causes a long-term reliability and various thermal problems in microelectronics. In this study, liquid cooling method was investigated using straight microchannels with various metal bumps. Microchannels were fabricated on Si wafer using deep reactive ion etching (DRIE), and Ag, Cu, or Cr/Au/Cu metal bumps were placed on Si wafer by a screen printing method. The surface temperature of liquid cooling structures with various metal bumps was measured by infrared (IR) microscopy. For liquid cooling with Cr/Au/Cu bumps, the surface temperature difference before and after liquid cooling was $45.2^{\circ}C$ and the power density drop was $2.8W/cm^2$ at $200^{\circ}C$ heating temperature.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.4
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• pp.31-36
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• 2015

The demand for multi-functionality, high density, high performance, and miniaturization of IC devices has caused the technology paradigm shift for electronic packaging. So, thermal management of new packaged chips becomes a bottleneck for the performance of next generation devices. Among various thermal solutions such as heat sink, heat spreader, TIM, thermoelectric cooler, etc. on-chip liquid cooling module was investigated in this study. Micro-channel was fabricated on Si wafer using a deep reactive ion etching, and 3 different micro-channel designs (straight MC, serpentine MC, zigzag MC) were formed to evalute the effectiveness of liquid cooling. At the heating temperature of $200^{\circ}C$ and coolant flow rate of 150ml/min, straight MC showed the high temperature differential of ${\sim}44^{\circ}C$ after liquid cooling. The shape of liquid flowing through micro-channel was observed by fluorescence microscope, and the temperarue differential of liquid cooling module was measuremd by IR microscope.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.3
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• pp.384-393
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• 2002

The effects of hole expansion angle and the arrangement of nozzles on a film cooling system for a turbine-blade-shaped surface were experimentally investigated. Liquid crystal with flue-temperature correlation and an image processing system were employed to evaluate surface temperature. Distributions of cooling effectiveness were then presented to figure out the change of heat transfer characteristics with different geometric conditions of cooling-holes. It was found thats the averaged cooling efficiency on the suction surface was maximum with 10 degree of the cooling hole expansion angle. It was also shown that the averaged cooling efficiency on the pressure surface and the averaged cooling efficiency for dual array case were not affected by the hole expansion angle.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1864-1869
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• 2007

In this study, we compare thermal performance between four different types of cold plates for humanoid robot cooling. Two commercially available cold plates made of copper have different dimensions and internal flow paths: One has $20{\times}20$ $mm^2$ base area with micro-channels and the other has $62.5{\times}62.5$ $mm^2$ base area with 85 round pin-fins. And two different types of cold plates of $20{\times}20$ $mm^2$ base area with 7 mm high are made of PC (polycarbonate), which aims to reduce the weight of cooling system. All cold plates are mounted on a $20{\times}20$ $mm^2$ copper block with two cartridge heaters of 30 $W/cm^2$. The overall heat transfer coefficient and thermal resistances for the liquid-cooled cold plates are obtained. The copper cold plate with micro-channels showed the best performance. Polycarbonate cold plates display fairly good thermal performance with more reduced system weight.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.8
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• pp.69-76
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• 2003

For stable combustion and safety of a structure of the propulsion system, a cooling system to the liquid rocket engine should be incorporated. In this study, Eulerian-Lagrangian scheme for two phase combustion, nongray radiation and soot formation effect, and film-wall interaction have been introduced to study the effect of film cooling. After briefly introducing the governing equation, combustion characteristics with change of wall temperature has been investigated by varying such parameters as fuel mass fraction for film cooling, diameter of the fuel droplet, overall mixture fraction of oxygen to fuel. Also, radiative heat flux is compared with the conductive one at the combustor wall.