• Nuclear Engineering and Technology
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• 제47권4호
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• pp.389-397
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• 2015

The effects of mixing vanes (MVs) attached to a grid spacer on the characteristics of air-water annular flows were experimentally investigated. To know the effects, a grid spacer with or without MV was inserted in a vertical circular pipe of 16-mm internal diameter. For three cases (i.e., no spacer, spacer without MV, and spacer with MV), the liquid film thickness, liquid entrainment fraction, and deposition rate were measured by the constant current method, single liquid film extraction method, and double liquid film extraction method, respectively. The MVs significantly promote the re-deposition of liquid droplets in the gas core flow into the liquid film on the channel walls. The deposition mass transfer coefficient is three times higher for the spacer with MV than for the spacer without MV, even for cases 0.3-m downstream from the spacer. The liquid film thickness becomes thicker upstream and downstream for the spacer with MV, compared with the thickness for the spacer without MV and for the case with no spacer.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.1479-1482
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• 2009

Compared with tilt transfer wet station, vertical etching system has a variety of advantages that are 50% space savings, higher throughput, fairly good etch uniformity over an entire glass for thin film transistor application. The aim of the present work is to study on a vertical etching system to improve the process factors. The computational fluid dynamics analysis is used to demonstrate the change of the etch uniformity as a function of tilt angle of the glass substrate.

• Journal of Advanced Marine Engineering and Technology
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• 제11권1호
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• pp.72-79
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• 1987

When the wall temperature is very high, a stable vapor film covers the heat transfer surface. The vapor film creates a strong thermal resistance when heat is transferred to the liquid though it. This phenomenon, called "film boiling" is very important in the heat treatment of metals, the design of cryogenic heat exchangers, and the emergency cooling of nuclear reactors. In the practical engineering problems of the transient cooling process of a high temperature wall, the wall temperature history, the variation of the heat transfer coefficients, and the wall superheat at the rewetting points, are the main areas of concern. These three areas are influenced in a complex fashion such factors as the initial wall temperature, the physical properties of both the wall and the coolant, the fluid temperature, and the flow state. Therefore many kinds of specialized experiments are necessary in the creation of precise thermal design. The object of this study is to investigate the heat transfer characteristics in the transient cooling process of a high temperature wall. The slow transient cooling experiment was carried out with a copper block of high thermal capacity. The block was 240 mm high and 79 mm O.D.. The coolant flowed throuogh the center of a 10 mm diameter channel in the copper block. In the copper block, three sheathed thermocouples were placed in a line perpendicular to the flow. These thermocouples were used to take measurements of the temperature histories of the copper block.

• 대한기계학회논문집B
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• 제30권12호
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• pp.1236-1242
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• 2006

The local heat flux of spray cooling in the film boiling region were experimentally investigated for the spray region of $D_{max}$ = $0.005{\sim}0.03m^3/(m^2s)$. A twin-fluid full cone spray nozzle was employed for the experiment and the distributions of droplet flow rates were obtained for air-water full cone sprays. A stainless steel block was cooled down from initial temperature of about $800^{\circ}C$ by full cone spray. In the region near the stagnation point, it was found that the experimental data are in good agreement with the results predicted from the correlations between the local heat transfer and the local droplet flow rate proposed in the previous report. However, it was found that the experimental data of $D_r$ > $0.01m^3/(m^2s)$ are a little smaller than the results predicted from the correlations.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2000년도 춘계 학술발표회 논문집
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• pp.197-200
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• 2000

• 대한기계학회논문집
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• 제19권9호
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• pp.2386-2398
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• 1995

The paper describes the results of an experimental investigation of the heat transfer rate on the endwall surface within the plane turbine cascade passage and includes the effect of the heat transfer for the two different boundary layer thicknesses and Reynolds numbers. The limiting streamlines on the endwall surface have been visualized by the oil film method in order to compare with the endwall heat transfer. The hue-capturing method using the termochromatic liquid crystals with great spatial resolution has been used to provide the local distribution of the endwall heat transfer coefficients. Because the detailed contours of the local heat transfer coefficients over the entire endwall can be obtained from the hue-capturing method, it has been possible to obtain information on the endwall heat transfer within the plane turbine cascade passage from these heat transfer contours.

• 설비공학논문집
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• 제13권5호
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• pp.422-430
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• 2001

In the present study, an evaporative generation process of ammonia-water solution film on the vertical plate was analysed. For the utilization of waste heat, hot water of low temperature was used as the heat source. The continuity, momentum, energy and diffusion equations for the solution film and vapor mixture were formulated in integral forms and solved numerically. Counter-current solution-vapor flow resulted in the refrigerant vapor of the higher ammonia concentration than that of co-current flow. Eve the rectification of refrigerant vapor was observed near the inlet of solution film in counter-current flow. For the optimum operation of generator using hot water, numerical experiments, based on the heat exchange and generation efficiencies. revealed the inter-relationships among the Reynolds number of the solution film and hot water, and the length of generator. Enhancement of heat and mass transport in the solution film was found to be very effective for the improvement of generation performance, especially at high solution flow rate.

• 한국농공학회논문집
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• 제52권5호
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• pp.11-18
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• 2010

This study was conducted to provide design data for deciding covering method in double layers greenhouse. The variation of photosynthetic photon flux (PPF) and heat flow in air inflated and conventional double layers greenhouse was analyzed. The PPF of air inflated double covering greenhouse was less than that of conventional greenhouse during summer season because the more PPF comes into conventional greenhouse through roof vent which was rolled up for ventilation. The air inflated double layers covering greenhouse was superior to conventional type in the aspect of controlling inside temperature down owing to lower irradiation. The PPF of air inflated greenhouse was greater than that of conventional greenhouse during winter season because the transmittance of conventional greenhouse decreased by dust collected on inside plastic film nearly closed for insulation. Considering the PPF not sufficient for tomato growing in winter, the air inflated double covering system with the greater transmittance was better than conventional covering system. When the inside air of air inflated greenhouse was injected into space between the double layers of covering, the PPF of air inflated greenhouse was much less than the conventional greenhouse because the transmittance of air inflated double covering decreased due to condensation of highly humidified inside air. It was concluded that the more dried outside air should be used for inflating double layers covering. The heat insulation performance of air inflated double covering system was superior to conventional double covering system when comparing the overall heat transfer coefficients for each covering method. However the differences among the overall heat transfer coefficients depending on difference between inside and outside temperatures of greenhouse were great, it is necessary to conduct additional experiment for investigating the overall heat transfer coefficient to design the double layers covering.

• 대한안전경영과학회지
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• 제19권4호
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• pp.317-322
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• 2017

When the heat flux on the heating surface following changing heat condition in the boiling heat transfer system exceeds critical heat flux, the critical heat flux phenomenon is going over to immediately the film boiling area and then it is occurred the physical destruction phenomenon of various heat transfer systems. In order to maximize the safe operation and performance of the heat transfer system, it is essential to improve the CHF(Critical Heat Flux) of the system. Therefore, we have analysis the effect of improving CHF and characteristics of heat transfer following the nanoparticle coating thickness. As the results, copper nanocoating time are increased to CHF, and in case of nano-coatings are increased spray-deposited coating times more than in the fure water; copper nanopowder is increased up to 6.40%. The boiling heat transfer coefficients of the pure water are increased up to 5.79% respectively. Also, the contact angle is decreased and surface roughness is increased when nano-coating time is increasingly going up.

• 설비공학논문집
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• 제3권1호
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• pp.51-60
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• 1991

The aim of this study is to investigate the heat transfer characteristics in the transient cooling process of a high temperature wall. The slow transient cooling experiment was carried out with a copper block of high thermal capacity. The results of these experiments are as follows. 1. Temperature histories measured by the thermocouple, which is 0.99, 2.00, 2.99mm from the heat transfer surface showed monotonous during the cooling process. These variation are the curves of typical temperature histories in film-boiling, transition-boiling, and nucleate-boiling regions. 2. The temperature histories were measured by thermocouple installed in the copper block. The variations of the surface heat fluxes and surface temperature were computed from the numerical solution method TDMA from the measured temperature histories for radial position one dimensional heat transfer inverse problem. The boiling curves were found by the computed temperature histories. 3. The rewetting point which starts to change from film boiling to nucleate boiling is not connected with the mass velocity and it were found that the temperature of rewetting point indicated about $100^{\circ}C$. 4. The heat flux of rewetting point was about $10^5Kcal/m^2h$, at that time, the heat transfer coeficient indicated about $1000Kcal/m^2h^{\circ}C$ irrelevent to mass velocity. 5. The wall superheat decreases as the pressure increases. But I found that rewetting point appeared under higher condition in the wall temperature.