• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.4
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• pp.472-483
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• 1999

The evaporation heat transfer and pressure drop characteristics for HFC-l34a in flat plate type heat exchangers with enhanced beads were experimentally investigated. Three plate type evaporators with different geometric condition of U-turn area were tested. Mass fluxes were tested over the range of 83kg/$m^2$s to 166kg/$m^2$s, and heat fluxes were varied from 4㎾/$m^2$ to 12㎾/$m^2$. Evaporation temperature was 5$^{\circ}C$ with inlet qualities of 0.1 to 1.0. There was no notable difference in the heat transfer coefficient by geometric variation of U-turn area, but the third plate with cross-ribbed channel at U-turn area was better than others in the evaluation using volume goodness factor comparison. Also, the mixtures of HFC-l34a and PAG oil was tested to determine oil effects on heat transfer and pressure drop. As oil concentration was increased, heat transfer coefficient was increased by 22~48% up to the 3wt.%, but decreased by 14~22% at the 4wt.%. The pressure drop was increased by the maximum of 100% as oil concentration was increased.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.268-273
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• 2001

A fundamental study on the harvest-type ice storage system applied ice making method in-water and its temperature characteristics in ice storage system was performed experimentally of the charge and discharge of cold. This paper is concerned with the development of a new method for making and separating ice and saving floated ice by installing an evaporation plate at in-water within a storage tank. In a conventional harvest-type ice storage system, a tank saves ice by separating a formed ice from an installed evaporation plate, which is located above an ice storage tank as an ice storage system. A new harvest-type method shows very good heat transfer efficiency than a convectional method. It is because the evaporation panel is directly contacted with water in a storage tank. Also, at a conventional system a circulating pump, a circulating water distributor and a piping are installed, but these components are not necessary in a new method. In this study two kinds of ice storage systems are experimentally investigated to study the thermal characteristics of ice storage tanks.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.4
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• pp.414-420
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• 2013

We developed inkjet based measurement system for micro-droplet behavior on a substrate. By using the inkjet dispenser, a droplet, which is as small as few pico-liter in volume, can be jetted and the amount can be controlled. After jetting, the droplet image on the substrate is acquired from side view camera. Then, droplet profile is extracted to measure droplet volume, contact angle and evaporation characteristics. Also top view image of the droplet is acquired for better understanding of droplet shape. The previous contact angle measurement method has limitations since it mainly measures the ratio of height and contact diameter of droplet on a substrate. Unlike previous measurement system, our proposed method has advantages because various behavior of droplet on substrate can be effectively analyzed by extracting the droplet profile.

• Journal of Powder Materials
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• v.9 no.2
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• pp.89-95
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• 2002

Spherical fine powders of tungsten oxide powders were prepared by the emulsion evaporation method. The characteristics of the powders prepared were examined by means of TGA, X-ray diffraction, SEM and image analysis. The emulsions were prepared by fast mixing of aqueous phase containing tugsten and the organic phase which composed of kerosene, surfactant, and paraffin oil. Precursors were made by evaporating the emulsionin the kerosene bath at $160^{\circ}C$, and then calcined at $650^{\circ}C$ in order to produce tungsten oxide powders. The average particle size of the tungsten oxide powders was $0.5\mutextrm{m}$ and their shapes were spherical at the both case of w/o and o/w type emulsions. As the HLB value of the surfactant increased and the concentration of tungsten ions decreased the mean particle siqe of tungsten oxide powders decreased whereas agglomerationsize increased. The optimum concentration of Span 80 was 8 percent by volume, and the optimum stirring speed in the emulsion formation was 5000 rpm in order to obtain fine and well dispersed $WO_3$ powders.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.1
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• pp.165-176
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• 1996

The flow field and spray characteristics for loop scavenged type 2stroke engine having pancake shape was numerically computed using KIVA-Ⅱ code. The cylinder has 1intake port, 2side intake ports and 1exhaust port with induced flow angle 25 deg. In engine calculation, the chop techniques is used to strip or add planes of cells across the mesh adjacent to the TDC and the BDC(ports parts) for preventing the demand of exceed time during the computation, providing a control on cell height in the squish region. The modified turbulent model including the consideration of the compressibility effect due to the compression and expansion of piston was also used. The case of 25 deg.(injection angle) which is opposite to scavenging flow direction shows better the distribution of droplets and the evaporation rate of droplets compared to other cases(0 deg., - 25 deg.). When injection pressure was increased, the spray tip penetration became longer. When injection pressure was increased, the interaction between the upward gas velocity and spray droplets strongly cause. Thus the breakup of droplets is strongly occurred and the evaporation rate of droplets was found to be better.

• 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.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.247-251
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• 2007

Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristics of carbon dioxide flowing upward in a vertical micro-fin tube have been investigated by experiment. Before a test section, a pre-heater is installed to adjust the inlet quality of the refrigerant to a desired value. The micro-fin tube with outer diameter of 5 mm and length of 1.44 m was selected as the test section. The test was conducted at mass fluxes of 318 to $530\;kg/m^2s$, saturation temperature of -5 to $5^{\circ}C$, and heat fluxes of 15 to $30\;kW/m^2$. As the vapor quality increases, the heat transfer coefficients of carbon dioxide are increased, and the heat transfer coefficients increase when the heat fluxes and saturation temperatures increase, and there was not much of influence of mass flux on the heat transfer coefficients.

• Journal of ILASS-Korea
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• v.15 no.1
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• pp.31-37
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• 2010

The aim of this work is to investigate the spray and combustion characteristics of dimethyl-ether (DME) at various injection conditions. The spray characteristics such as spray tip penetration and spray cone angle were experimentally studied from the spray images which obtained from the spray visualization system. Combustion and emissions characteristics were numerically investigated by using KIVA-3V code coupled with Chemkin chemistry solver. From these results, it revealed that DME spray had a shorter spray tip penetration and wider spray cone angle than that of diesel spray due to the low density, low surface tension, and fast evaporation characteristics. At the constant heating value condition, DME fuel showed higher peak combustion pressure and earlier ignition timing, because of high cetane number and superior evaporation characteristics. In addition, the combustion of DME exhausted more $NO_x$ emission and lower HC emission due to the active combustion reaction in the combustion chamber. The result shows that DME had a little soot emission due to its molecular structure characteristics with no direct connection between carbons.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.41-47
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• 1999

The burning rate of solid propellant is one of the key parameter associated with the dynamic characteristics of combustion and the combustion performances. In the AP propellants, the evaporation on the reacting surface as well as the decomposition of the propellant is of great importance in determining the overall burning rate. In this study, a theoretical analysis was conducted to obtain the expression for burning rate in the steady state combustion with the energy and species equations in the condensed phase when the radiative heat flux partially contributes to the total heat transfer to the propellant surface.

• Journal of Hydrogen and New Energy
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• v.8 no.2
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• pp.57-65
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• 1997

Thermal analysis has been performed to design a high-performance $LH_2$ vessel with about 1% per day evaporation loss. Analysis includes the combined insulations of MLI(Multi-Layer Insulation) and VCS (Vapor-Cooled Shield) under high vacuum. Combined insulation of MLI and VCS shows the existence of optimal location of VCS to minimize evaporation loss. Comparison of parallel-type DVCS (Double Vapor-Cooled Shield) and serial-type DVCS is also made to show the effectiveness of the system. The results indicate that the serial-type DVCS vessel is better than the parallel-type DVCS vessel with respect to overall evaporation loss. The combined insulation of SVCS (Single Vapor-Cooled Shield) with a partial MLI can give a similar performance characteristics compared to that with MLI and DVCS.