• Journal of Hydrogen and New Energy
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• 제26권3호
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• pp.234-240
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• 2015

In the face of the world's growing energy storage needs, liquid hydrogen offers a high energy density solution for the storage and transport of energy throughout society. A 5 L liquid hydrogen storage tank has been designed, fabricated and tested to investigate boil-off rate of liquid hydrogen. As the insulation plays a key role on the cryogenic vessels, various insulation methods have been employed. To reduce heat conduction loss, the epoxy resin-based insulation supports G-10 were used. To minimize radiation heat loss, vapor cooled radiation shield, multi-layer insulation, and high vacuum were adopted. Mass flow meter was used to measure boil-off rate of the 5 L cryogenic vessel. A series of performance tests were done for liquid nitrogen and liquid hydrogen to compare with design parameters, resulting in the boil-off rate of 1.7%/day for liquid nitrogen and 16.8%/day for liquid hydrogen at maximum.

• The KSFM Journal of Fluid Machinery
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• 제19권6호
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• pp.50-54
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• 2016

The performance of a scroll expander is the most important factor for the efficiency of small scale Organic Rankine cycle waste heat power generation systems. In this research, a scroll compressor was purchased and operated in reverse to function as a scroll expander. With air as a working fluid, a series of performance test were conducted on this expander by varying the inlet and outlet pressure. Secondly, We have tested through 2000 to 3500 rpm rotational speed to find the maximum power and efficiency of the expander. And last, It was observed in the initial experiments that the design of the expander's orbiting scroll wrap partially blocked the fluid intake which may have caused unnecessary flow resistance. To verify this theory, a small part of the scroll wrap was removed and the performance test was redone. It was observed that the lower back pressure assure the higher efficiency and power of expander and the rotational speed that shows maximum adiabetic efficiency of scroll expander is 69% at 2500 rpm. And by modified wrap of the scroll, we could get volume flow rate for 13% to 19% and power for 5% to 18% increased. But the maximum efficiency of the modified scroll was decreased 8%.

• Journal of Power System Engineering
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• 제5권2호
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• pp.22-29
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• 2001

This paper represents axial mean velocity, turbulent kinetic energy and swirl number based on momentum flux measured in the X-Y plane and Y-Z plane respectively of a cone type gas swirl burner by using X-probe from the hot-wire anemometer system. This experiment is carried out at flow rates 350 and $450{\ell}/min$ respectively, which are equivalent to the combustion air flow rate necessary for heat release 15,000 kcal/hr in gas furnace, in the test section of a subsonic wind tunnel. Axial mean velocities and turbulent kinetic energies show that their maximum values exist centering around narrow slits situated radially on the edge of and in the forefront of a burner until $X/R{\fallingdotseq}1.5$, but they have a peculiar shape like a starfish diffusing and developing into inward and outward of a burner by means of the mixing between flows ejected from narrow slits, an inclination baffle plate and swirl vanes respectively according to downstream regions. Moreover, they show a relatively large value in the inner region of 0.5$S_m$ obtained by integration of velocity profiles shows a characteristic that has an inflection point composing of the maximum and minimum value until X/R<3, but shows close agreement with the geometric swirl number after a distance of X/R=3.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제6권1호
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• pp.11-19
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• 1994

An optimal design for Gifford-McMahon/Joule-Thomson(GM-JT) refrigerators was performed by a numerical method. The design goal was to meet the cooling requirement for MRI systems, which was 3 Watt at 4 K. A general cycle analysis program was written to calculate the cooling capacity of the GM-JT refrigerators for the givenstage GM refrigerator. The program was executed for a specific refrigerator with various design parameters. The optimal values for the maximum cooling were found for the sizes of the heat exchangers, the mass flow rate of helium, and the compression pressure.

• Transactions of the Korean Society of Automotive Engineers
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• 제3권1호
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• pp.54-64
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• 1995

The effects of swirl on early flame development and late combustion characteristic were investigated using a high speed single-shot visualized 51 engine. LDV measurements were performed to get better understanding of the flow field in this combustion chamber. Spark plugs were located at half radius (R/2) and central location of bore. High speed schlieren photographs at 20,000 frames/sec were taken to visualize the detailed formation and development of the flame kernel with cylinder pressure measurements. This study showed that high swirl gave favorable effects on combustion-related performances in terms of the maximum cylinder pressure and flame growth rate regardless of spark position. However, at R/2 ignition the low swirl shown desirable effects at low engine speed gave worse performances as engine speed increased than without swirl. There were distinct signs of slow-down in flame growth during the period when the flame front expanded from 2.5mm in radius until it reached 5.0mm apparently due to the presence of ground electrode. There seemed to be heat transfer effect on the flame expansion speed which was evidenced in high swirl case by the slowdown of the late flame front presumably caused by relatively large heat loss from burned gas to wall compared with low- or no-swirl cases.

• Journal of the Korean Society for Precision Engineering
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• 제24권12호
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• pp.95-103
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• 2007

This paper presents a liquid cooling concept for heat rejection of high power electronic devices existing in notebook computers etc. The design, fabrication, and performance of the planar ECF pump and farced-liquid cooling system are summarized. The electro-conjugate fluid (ECF) is a kind of dielectric and functional fluids, which generates jet flows (ECF-jets) by applying static electric field through a pair of rod-like electrodes. The ECF-jet directly acts on the working fluid, so the proposed planar ECF pump needs no moving part, produces no vibration and noise. The planar ECF pump, consists of a pump housing and electrode substrate, achieves maximum flow rate and output pressure of $5.5\;cm^3/s$ and 7.2 kPa, respectively, at an applied voltage of 2.0 kV. The farced-liquid cooling system, constructed with the planar ECF pump, liquid-cooled heat sink and thermal test chip, removes input power up to 80 W keeping the chip surface temperature below $70\;^{\circ}C$. The experimental results demonstrate that the feasibility of forced-liquid cooling system using ECF is confirmed as an advanced cooling solution on the next-generation high power electronic devices.

• Journal of the Korean Society for Heat Treatment
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• 제31권4호
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• pp.180-186
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• 2018

High temperature flow behaviors of Fe-Cr-Mo-V-W-C tool steel were investigated using isothermal compression tests on a Gleeble simulator. The compressive test temperature was varied from 850 to $1,150^{\circ}C$ with the strain rate ranges of 0.05 and $10s^{-1}$. The maximum height reduction was 45%. The dynamic softening related to the dynamic recrystallization was observed during hot deformation. The constitutive model based on Arrhenius-typed equation with the Zener-Hollomon parameter was proposed to simulate the hot deformation behavior of Fe-Cr-Mo-V-W-C steel. An artificial neural network (ANN) model was also developed to compare with the constitutive model. It was concluded that the ANN model showed more accurate prediction compared with the constitutive model for describing the hot compressive behavior of Fe-Cr-Mo-V-W-C steel.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제27권6호
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• pp.300-306
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• 2015

For an asymmetric scroll compressor for heat pump application, a numerical simulation was carried out to investigate the effects of injection port design on the compressor's performance under gas injection. To validate the simulation, the numerical results were compared with experimental results obtained from a scroll compressor with a base injection port design. There was good agreement between simulation and experimental results, with around a 1% difference in the injection mass flow rate when the injection pressure was below $12kgf/cm^2A$ for the heating mode. Various injection port angular positions were numerically tested to yield better injection performance. The largest improvement in heating capacity was obtained at angles of $240^{\circ}$ and $200^{\circ}$ inward from the scroll wrap end angle for low-temperature and standard heating conditions, respectively, while the maximum COP improvement was at $365^{\circ}$ and $280^{\circ}$, respectively. A considerable improvement in cooling capacity was also found at the injection port angle of $240^{\circ}$.

• Journal of the Korean Solar Energy Society
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• 제31권3호
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• pp.73-79
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• 2011

ORC(organic Rankine cycle) has potential of reducing consumption of fossil fuels and has many favorable characteristics to exploit low-temperature heat sources. This work analyzes performance of ORC with superheating using low-temperature energy sources in the form of sensible energy. Maximum mass flow rate of a working fluid relative to that of a source fluid is considerd to extract maximum power from the sources. Working fluids of R134a, $iC_4H_{10}$ and $C_6C_6$, and source temperatures of $120^{\circ}C$, $200^{\circ}C$ and $300^{\circ}C$ are considered in this work. Results show that for a fixed source temperature thermal efficiency increases with evaporating temperaure, however net work per unit mass of source fluid has a maximum with respect to the evaporating temperature in the range of low source temperature. Results also show that the maximum power extraction is possible with R134a for the source temperature of $120^{\circ}C$, with $iC_4H_{10}$ for $200^{\circ}C$, and with $C_6C_6$ for $300^{\circ}C$.

• Textile Coloration and Finishing
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• 제26권2호
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• pp.114-123
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• 2014

This research investigated the physical properties of PET coolness filaments and their knitted fabrics including dyeing characteristics of these knitted fabrics according to the different dyeing time and temperature. The coolness filament(S) with non-circular cross-section and hydrophilic property was spun and another commercialized coolness(A) and regular(R) PET filaments were prepared for comparing coolness and another physical properties. Qmax of coolness knitted fabric made with S filament was higher than that of R-PET filament, and the maximum value of Qmax of S knitted fabric was shown at the dyeing conditions of temperature, $110^{\circ}C$ with 30 min. or 40min. It was shown that hand of S knitted fabric was a little harsh comparing to A and regular knit specimens, but shape retention and wearing performance of garment made with S knit specimen were estimated as good owing to high bending and shear rigidity. K/S of S knitted fabric was higher than those of regular PET and A knit specimens. Dyeing fastness of coolness knitted fabric showed between 4th and 5th grade.