• International Journal of Air-Conditioning and Refrigeration
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• 제16권4호
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• pp.130-136
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• 2008

The refrigerant R-134a flow distributions are experimentally studied for a round header/ten flat tube test section simulating a brazed aluminum heat exchanger. Three different inlet orientations(parallel, normal, vertical) were investigated. Tests were conducted with downward flow for the mass flux from 70 to 130 $kg/m^2s$ and quality from 0.2 to 0.6. In the test section, tubes were flush-mounted with no protrusion into the header. It is shown that normal and vertical inlet yielded approximately similar flow distribution. At high mass fluxes or high qualities, however, slightly better results were obtained for normal inlet configuration. The flow distribution was worst for the parallel inlet configuration. Possible explanation is provided based on flow visualization results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2182-2185
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• 1999

In this experimental study we propose the double dielectric barrier discharge(DDBD) reactor to produce as high an electric field as possible. DDBD reactor is designed to remove $NO_x$ at atmospheric pressures from the moving pollution source such as diesel automobile DDBD reactor consisted of two cylinder glass tubes arranged so that the gas flow was directed between the two tubes. Inside of the inner tube was filled with small metal beads and outside of the inner tube was wounded with stainless wire to form the electrode. The outer tube was surrounded by an aluminum foil In this reactor there are three electrodes, i.e. metal bead(C), helical wire(I) and aluminum foil(0). By using DDBD reactor we will report some interesting results of treatment of the gas which is the dilute mixtures of NO in N2. And then we compared thee results with the results of cylinder-wire(CW) which is one of popularly used reactor in non-thermal plasma applications.

• 농업생명과학연구
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• 제44권4호
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• pp.29-43
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• 2010

The numerical analysis by using CFX 11.0 commercial code was done for proper design of the heat exchanger. The present experimental studies were also conducted to investigate the effects of circulating solid particles on the characteristics of fluid flow, heat transfer and cleaning effect in the fluidized bed vertical shell and tube type heat exchanger with counterflow, at which a variety of solid particles such as glass ($3mm{\Phi}$), aluminum ($2{\sim}3mm{\Phi}$), steel ($2{\sim}2.5mm{\Phi}$), copper ($2.5mm{\Phi}$) and sand ($2{\sim}4mm{\Phi}$) were used in the fluidized bed with a smooth tube. Seven different solid particles have the same volume, and the effects of various parameters such as water flow rates, particle diameter, materials and geometry were investigated. The present experimental and numerical results showed that the flow velocity range for collision of particles to the tube wall was higher with heavier density solid particles, and the increase in heat transfer was in the order of sand, copper, steel, aluminum, and glass. This behavior might be attributed to the parameters such as surface roughness or particle heat capacity.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.311-316
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• 2010

The ignition and the burning characteristics of aluminum and magnesium particles ($30-110{\mu}m$ in diameter) isolated due to electrodynamic levitation were experimentally investigated. The burning time, the ignition delay time, the flame temperature, and the flame diameter were measured. The thermal radiation intensity was measured using the photomultiplier tube and the combustion history was monitored by high-speed cinematography. Two-wavelength pyrometry measured the temperature of the burning particles. The burning times of aluminum particles were measured approximately 5 to 8 times longer than those of magnesium particles. Exponents of $D^n$-law, for the burning rate of magnesium and aluminum particles of diameters less than $110{\mu}m$, are found to be 0.6 and 1.5, respectively. The instant of aluminum ignition is clearly distinguished with the ignition delay time little less than 10 ms, however the burning history of magnesium particle exhibits no distinct instant of the ignition. The ignition delay time of magnesium particle (less than $110{\mu}m$) were approximately shown in the range from 50 to 200 ns. The flame temperatures of single metal particles are lower than the boiling point of the oxide. The nondimensional flame diameters for magnesium are decreased with increasing of the diameter. The nondimensional flame diameters for aluminum are not changed significantly.

• 소성∙가공
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• 제12권3호
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• pp.214-220
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• 2003

In the case of hollow cylinder extrusion using porthole die, the effects of extrusion parameters-temperature, the speed of extrusion, the shape of the die and mandrel-on metal flow in porthole die extrusion of aluminum have been investigated. There have been few studies about condenser tube extruded by porthole die. This study was designed to evaluate metal flow, welding pressure, extrusion load, tendency of mandrel deflection according to variation of chamber length in porthole die. The welding chamber height in condenser tube was calculated by using finite element method. Forming analysis results for condenser tube would provide useful information for the optimal design of porthole die.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1079-1083
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• 2009

In this study, the distribution of $CO_2$ in an evaporator with 10 parallel micro channel aluminum tubes are experimentally investigated. Each tube has 6 circular micro channels with a diameter of 0.8mm. The tubes are heated with electric resistance wires, and the distribution of $CO_2$ into each tube is investigated by measuring the outer wall temperature. The outer wall temperature was found to be higher at the exit part of the top tube. It is thought that the $CO_2$ vapor at the upper part of the header reduces the mass flow rate of $CO_2$ into the top tube.

• 설비공학논문집
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• 제11권1호
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• pp.10-17
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• 1999

The present work presents condensation heat transfer and pressure drop data for the flow of R-12 in flat extruded aluminum tubes with small hydraulic diameters. The tube outside dimensions are $18mm(width){\times}1.7mm(height)$. Three types of internal geometry with the same outside dimensions are tested : sample 1 (7 tube holes), sample 2 (13 tube holes) and sample 3 (7 tube holes, micro-fin). The overall heat transfer coefficient is obtained for air-to-refrigerant heat transfer, and the Wilson plot method is used to determine the heat transfer coefficient for refrigerant flow. The sample 2 and sample 3 show significantly higher performance than sample 1. The heat transfer rates for the sample 2 and sample 3 are 9% and 12% higher, respectively, than sample 1. The friction factors for the sample 2 and sample 3 are 11.9% and 2.4% higher, respectively, than sample 1.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1267-1276
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• 1998

Falling-film evaporation experiments with aqueous lithium bromide (LiBr) solution were performed to investigate the heat transfer characteristics of enhanced copper tubes. Enhanced tubes (a knurled tube, a spirally grooved tube, and a tube coated with $20{\mu}m$ aluminum particles) and a bare tube were selected as test specimens. Averaged evaporation fluxes of water were obtained from horizontal tubes with various film Reynolds numbers, system pressures, LiBr concentrations and degrees of wall superheat. The enhanced performance of steam generation was compared between tubes with varying parameters. The knurled tube geometry showed the most excellent performance among the tubes tested. The specified enhanced tubes were more useful for generating steam on a low grade heat source such as waste heat.

• 한국자동차공학회논문집
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• 제6권3호
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• pp.177-186
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• 1998

For the purpose of finding out the sound field characteristics in a cavity of a rectangular enclosure with foamed aluminum lining, analytical and experimental studies are performed with random noise input. Experimental method using two-microphone impedance tube measures the absorption coefficients and the impedances of simple sound absorbing materials. Measured acoustical parameters of the test samples are applied to the theoretical analysis to predict sound pressure field in the cavity. The sound absorp- tion effects from measurements are compared to prediction in both cases with and without foamed aluminum lining in the cavity of the rectangular enclosure.

• 한국산학기술학회논문지
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• 제16권5호
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• pp.3006-3013
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• 2015

원관 열교환기보다 납작관 열교환기를 사용하면 전열성능을 한층 향상시킬 수 있다. 납작관 열교환기를 적절히 설계하기 위해서는 관 내측 열전달계수를 알아야 한다. 본 실험에서는 수력직경 1.41mm인 알루미늄 납작관 내 R-410A 대류 비등 열전달계수를 구하였다. 실험범위는 질량유속 $200{\sim}600kg/m^2s$, 열유속 $5{\sim}15kg/m^2$, 포화온도 $5{\sim}15^{\circ}C$이다. 실험 결과 열전달계수는 임계 건도를 기점으로 감소함을 보였다. 임계 건도는 열유속이 증가할수록 감소하고, 질량유속이 감소할수록 감소하였다. 이는 높은 열유속 또는 낮은 질량유속에서 대류의 영향이 작게 되고 따라서 조기에 dryout이 발생되기 때문에 나타나는 현상으로 판단된다. 열전달계수는 질량유속이 증가할수록 증가하였다. 그러나 낮은 건도에서는 질량유속의 영향은 미미하였다. 열전달계수는 포화온도가 증가할수록 증가하였다. 하지만 이런 경향은 열유속이 작아지면 감소하였다. Shah와 Kaew-On et al. 상관식은 본 실험자료를 적절히 예측하였다.