• Korean Journal of Optics and Photonics
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• v.31 no.4
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• pp.176-182
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• 2020

The possibility of replacing the condensing-prism film used in conventional backlight units with a light-guide plate engraved with a submicrometer-periodic diffraction grating was investigated. The optimal period for the diffraction grating was determined through simulation and experiment, and the transmission-mode efficiency of the diffraction grating was calculated in terms of the polar angle and azimuthal angle of the incident light. In addition, the effects of the two methods of optimizing the polar angle and the directional angle were compared by simulation, by suggesting the shape and configuration of the light-guide plate, so that more light could be extracted by diffraction. By using a ray-tracing program, the luminance angular distribution of the light-guide plate engraved with the diffraction grating was calculated and compared to the luminance angular distribution for each actual prototype.

• Journal of Power System Engineering
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• v.8 no.1
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• pp.41-47
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• 2004

Cooling towers are widely used not only for cooling products and equipment in manufacturing process but HVAC(Heating, Ventilation and Air Conditioning) system. As a cooling tower is the terminal apparatus which discharges heat from industrial process, the efficiency of heat exchange in the cooling tower greatly affects to the overall performance of a thermal system. In this paper, we constituted a new water cooling system by using a Latent heat of evaporation in an enclosed tank, and this system is consisted of an enclosed vacuum tank and water driven ejector system. Several experimental cases were carried out for improvement methods of high vacuum pressure and water cooling characteristics. The ejector performance was tested in case of water temperature variations that flows into the ejector. Based on the vacuum pressure by water driven ejector, the water cooling characteristics were investigated for the vaporized air condensing effects.

• Nuclear Engineering and Technology
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• v.42 no.3
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• pp.297-304
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• 2010

In the design of advanced light water reactors (ALWRs) and in the safety assessment of currently operating nuclear power plants, it is necessary to evaluate the possibility of experiencing a degraded core accident and to develop innovative safety technologies in order to assure long-term debris cooling. The objective of this experimental study is to investigate the enhancement factors of dryout heat flux in debris beds by coolant injection from below. The experimental facility consists mainly of an induction heater, a double-wall quartz-tube test section containing a steel-particle bed and coolant injection and recovery condensing loop. A fairly uniform heating of the particle bed was achieved in the radial direction and the axial variation was within 20%. This paper reports the experimental data for 3.2 mm and 4.8 mm particle beds with a 300 mm bed height. The dryout heat density data were obtained for both the top-flooding and the forced coolant injection from below with an injection mass flux of up to $1.5\;kg/m^2s$. The dryout heat density increased as the rate of coolant injection increased. At a coolant injection mass flux of $1.0\;kg/m^2s$, the dryout heat density was ${\sim}6.5\;MW/m^3$ for the 4.8 mm particle bed and ${\sim}5.6\;MW/m^3$ for the 3.2 mm particle bed. The enhancement factors of the dryout heat density were 1.6-1.8.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.459-467
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• 2004

This paper presents an efficient reanalysis algorithm, named PRAS (Partial Reanalysis algorithm using Adaptable Substructuring), for the partially changed structures. The algorithm recalculates directly any displacement or member force under consideration in real time without a full reanalysis in spite of local changes in member stiffness or connectivity_ The key procedures consists of 1) partitioning the whole structure into the changed part and the unchanged part, 2) condensing the internal degrees of freedom and forming the unchanged part substructure, 3) assembling and solving the new stiffness matrix from the unchanged part substructure and the changed members.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.116-122
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• 2005

This study concerns the performance of condensing heat transfer in two-phase closed thermosyphons with various helical grooves. Distilled water, methanol, ethanol have been used as the working fluid. In the present work, a copper tube of the length of 1200mm and 14.28mm of inside diameter is used as the container of the thermosyphon. Each of the evaporator and the condenser section has a length of 550mm, while the remaining part of the thermosyphon tube is adiabatic section. A experimental study was carried out for analyzing the performances of having 50, 60, 70, 80, 90 helical grooves. A plain thermosyphon having the same inner and outer diameter as the grooved thermosyphons is also tested for the comparison. The type of working fluid and the numbers of grooves of the thermosyphons with various helical grooves have been used as the experimental parameters. The experimental results have been assessed and compared with existing theories. The results show that the type of working fluids are very important factors for the operation of thermosyphons. And the maximum enhancement (i.e. the ratio of the heat transfer coefficients the helical thermosyphons to plain thermosyphons) is $1.5{\sim}2$ for condensation.

• Journal of the Korean Society of Combustion
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• v.14 no.4
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• pp.7-16
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• 2009

Porous metal plates (Metal fiber, muti-hole metal plate) using mainly in surface burner are known to have a corrosion and durability problem under high temperature condition. In this study, premixed flat flame with perforated ceramic tile of more durable cordierite material was examined with respect to combustion stability and emission. The flat premixed ceramic burner consists of perforated ceramic tile and various type of baffle plates to form stable surface flame. The results show that most stable flat flame is generated using baffle plate with open ratio of 0.193. In downward flat flame mode which is widely used in condensing boiler, CO is measured below 50ppm from equivalence ratio 0.755 to 0.765 and $NO_X$ is measured below 12ppm from equivalence ratio 0.75 to 0.79. It is also found that the range of blue flame in flame stability curve becomes wider with increasing heat capacity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.2
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• pp.175-183
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• 2002

Flow Condensation heat transfer coefficients (HTCs) of Rl2, R22, R32, Rl23, Rl25, R134a, R142b were measured experimentally on a horizontal plain tube. The experi- mental apparatus was composed of three main parts; a refrigerant loop, a water loop and a water-glycol loop. The test section in a refrigerant loop was made of a copper tube of 8.8 mm inner diameter and 1000 mm length respectively. The refrigerant was cooled by passing cold water through an annulus surrounding the test section. All tests were performed at a filed refrigerant saturation temperature of 4$0^{\circ}C$ with mass fluxes of 100, 200, 300 kg/$m^2$s. The experimental result showed that flow condensation HTCs increase as the quality, mass flux, and latent heat of condensation increase. At the same mass flux, the HTCs of R32 and R142b were higher than those of R22 by 35~45% and 7~14% respectively while HTCs of R134a and Rl23 were similar to those of R22. On the other hand, HTCs of Rl25 and Rl2 were lower than those of R22 by 28 ~30% and 15 ~25% respectively Finally, a new correlation for flow condensation HTCs was developed by modifying Dobson and Chato's correlation with the latent heat of condensation considered. The correlaton showed an average deviation of 13.1% for all pure fluids data indicating an excellent agreement.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.2 s.146
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• pp.236-245
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• 2006

The ventilation performance for the various venting duct arrays has been experimentally compared in the scaled model of the container hold. Most container ships have the ventilation duct system to remove effectively the condensing heat released from container refrigerator. The existing duct system is vertically installed and basically has the number of duct as many as the columns of reefer container stack. In this study, to make up for the weak points having stagnantly hot legions in the centered area of container hold for the present system, the horizontal upward jotting duct system was proposed and proved by temperature rising tests on the scaled model. In this paper, the expected flow regimes and the thermal and hydrodynamic analogies as well as the measured temperature distributions in a hold for various duct types and heat released rates are deeply discussed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.10
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• pp.497-505
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• 2015

The evaporating temperature range required for the low temperature freezing system is from $-50^{\circ}C$ to $-30^{\circ}C$. Since it is difficult to keep the required capacity in a cabinet, it is advantageous to design the system using a cascade refrigeration system. Use of carbon dioxide and ammonia would be advantageous since ammonia is an environment-friendly working fluid and has a high capacity for performance improvement. To investigate the performance characteristics of the R744-R717 cascade refrigeration system, a theoretical model was developed and performance was analyzed according to cascade heat exchanger operating temperature. The optimal cascade R744 condensing temperature was $-5^{\circ}C$, and maximum COP was 1.13 when the temperature difference of the cascade heat exchanger was $5^{\circ}C$. In addition, the total system COP increased by 1.17 when the cascade temperature gap was $3^{\circ}C$ at the middle temperature of $-7.5^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.547-553
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• 1989

Last several stages of high capacity fossil power steam turbine and most stages of nuclear power steam turbine operate on wet steam. As a consequence, the flows in those cascades are accompanied by condensation, and the latent heat caused by condensation affects an oblique shock wave being generated at the vicinity of trailing of the blade. In the case of expanding of moist air through a suction type indraft wind tunnel, the effect of condensation affection the oblique shock wave generated by placing the small wedge into the supersonic part of the nozzle was investigated experimentally. In these connections, the relationship between condensation zone and reflection point of the incident oblique shock wave, angle between wedge bottom wall and oblique shock wave, and the variations of angles of incident and reflected shock waves due to the variation of initial stagnation relative humidity are discussed. Furthermore, the relationship between initial stagnation relative humidity and load working on the nozzle wall, obtained by measuring static pressure at the nozzle centerline, is discussed.