• 대한기계학회논문집B
• /
• 제24권4호
• /
• pp.485-494
• /
• 2000

The purpose of this paper is to investigate a critical heat flux(CHF) during forced convective subcooled and saturated boiling in free water jet system impinged on a rectangular heated surface. The surface is supplied with subcooled or saturated water through a rectangular jet. Experimental parameters studied are a width of heated surface, a height of supplementary water and a degree of subcooling. Incipient boiling point is observed in the temperature of 6${\~}8^{\circ}C$ of superheat of test specimen. CHF depends on jet velocity for various boiling-involved coolant system. CHF also is proportional to the nozzle exit velocity to the power of n, where n is 0.55 and 0.8 for subcooled and saturated boiling, respectively. CHF is enhanced with a higher jet velocity, higher degree of subcooling and smaller width of a heated surface.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1998년도 춘계학술발표회논문집(1)
• /
• pp.437-442
• /
• 1998

Film boiling is the heat transfer mechanism that can occurs when large temperature differences exist between a cold liquid and hot material. In the nuclear reactor safety analysis, film boiling has become an important issue in recent years. During severe accident, hot molten corium fall into relatively cool water, and fragment into spheres or sphere-like particles. If the steam explosion is triggered, the thermal energy of corium is converted into the mechanical energy that can threaten the integrity of reactor vessel or reactor cavity. One of the important concerns in the heat transfer analysis during pre-mixing stage is the film boiling heat transfer between the corium and water/steam two-phase flow. Until now, considerable works on film boiling heat been performed. However, there is no available correlation adequate for severe accident analysis. In this study, boiling heat transfer correlations have been developed, and their applicable ranges heat been enlarged and their prediction accuracy has been enhanced.

• 한국가시화정보학회:학술대회논문집
• /
• 한국가시화정보학회 2006년도 추계학술대회 논문집
• /
• pp.125-130
• /
• 2006

The characteristics of boiling heat transfer and critical heat flux (CHF) behavior of nano-fluids were studied by using various sized silver and alumina nanoparticles. The diameter of nanoparticles was from 2 nm to 250 nm for silver and from 20nm to 40nm for alumina. Pool boiling characteristics and CHF enhancement of nano-fluids with different sized nanoparticles were compared with those of pure water and each nano-fluids. The experiment was performed at atmospheric pressure and the temperature of the pool was maintained constantly by using a flat immersed heater. The concentration of nano-fluids was uniform in all experiments as 0.01g/liter. The results showed that the measured boiling curves were shifted to the right. It demonstrated that the occurrence of nucleate boiling regime in nano-fluids retarded, compared with that of pure water. Also, in nano-fluids, the boiling curves showed that CHF of nano-fluids is significantly enhanced and represented the effect of particle size on boiling characteristics.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제17권3호
• /
• pp.81-87
• /
• 2009

The effect of oil on convective boiling of R-123 in an enhanced tube bundle is experimentally investigated at $26.7^{\circ}C$ saturation temperature. The enhanced tube had pores (0.23 mm diameter) and connecting gaps (0.07 mm width), which had been optimized using pure R-123. The effects of oil concentration (0 to 5%), heat flux (10 to $40\;kW/m^2$), mass velocity (8 to $26\;kg/m2^s$) and vapor quality are investigated. The oil significantly reduces the bundle boiling heat transfer coefficient. With 1% oil, the reduction is approximately 35%. Further addition of oil further reduces the heat transfer coefficient. The data are also compared with the pool boiling counterpart. The reduction in the heat transfer coefficient is smaller in a bundle (convective boiling) than in a pool (single-tube pool boiling), with larger difference at a smaller heat flux. Similar to pure R-123 case, the effects of mass velocity and vapor quality are negligible for the convective boiling of R-123/oil mixture.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1997년도 추계학술발표회논문집(1)
• /
• pp.719-725
• /
• 1997

This paper presents results of experimental studies on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. As a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232$^{\circ}C$. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation beかeon the Nusselt number and the Rayleigh number in the molten metal Pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer.

• 대한기계학회논문집
• /
• 제12권1호
• /
• pp.44-47
• /
• 1988

본 실험에서는 온도측정용 써미스터인 고감도의 비드형 써미니스터를 이용하여 물의 감압증발에 의한 불등식 푸울내의 깊이 방향과 반경방향의 온도변화를 연속적으로 측정하여 연구한 결과를 보고한다.

• 한국항공우주학회지
• /
• 제42권2호
• /
• pp.119-126
• /
• 2014

본 연구에서는 연료가 비등점 이상의 고온으로 가열된 경우 오리피스 인젝터를 통해 분사되는 특성을 실험한 결과를 정리하였다. 크기가 다른 오리피스 인젝터 3종을 이용하여 3, 5, 10 bar의 분사압력을 가할 때 온도범위 $50{\sim}270^{\circ}C$에서 유량계수(${\alpha}$)를 측정하였다. 측정된 유량계수는 연료온도가 $180^{\circ}C$ 이하 영역에서는 점진적으로 감소하였으나 비등점인 $187^{\circ}C$를 넘어가면서 급격히 감소하였다. 비등점보다 높은 연료온도에서의 유량계수 감소 기울기는 분사압력에 따라 다른데, 특히 분사압력이 낮을수록 비등의 영향이 크게 작용하므로 더 급격한 특성을 보였다. 또한, 직경이 큰 인젝터의 유량계수가 더 크고, 낮은 연료온도 영역에서 난류-층류 천이현상으로 보이는 유량계수의 점프현상이 관찰되었다. 유량계수를 캐비테이션 수($K_c$)에 대하여 도시한 결과 인젝터의 크기가 작을 때는 연료 비등으로 인한 분사특성이 분사압력과 무관한 일정한 값을 가지는 것을 확인하였다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2009년 추계학술대회논문집
• /
• pp.218-222
• /
• 2009

A level-set (LS) method is presented for computation of boiling phenomena which involve liquid-vapor interfaces that evolve, merge and break up in time, the flow and temperature fields influenced by the interfacial motion, and the microlayer that forms between the solid and the vapor phase near the wall. The LS formulation for tracking the phase interfaces is modified to include the effects of phase change on the liquid-vapor interface and contact angle on the liquid-vapor-solid interline. The LS method can calculate an interface curvature accurately by using a smooth distance function. Also, it is straightforward to implement for two-phase flows in complex geometries. The numerical method is applied for analysis of nucleate boiling on a horizontal surface and film boiling on a horizontal cylinder.

• 한국환경과학회지
• /
• 제5권6호
• /
• pp.749-755
• /
• 1996

In order to grasp a characterization of low boiling point chlorinated organic compounds, this study which were carried out at the 8 stations for precipitation samples in the Pusan area during the period from February to September 1995. As a result, low boiling chlorinated organic compounds were estimated that it was dissolved by a portion of precipitation, and it be able to shift at the surface of the each. Concentration of low boiling point chlorinated organic compounds in precipitation are increased with increase of temperature, and estimated that air pollution compounds of as a rule in atmosphere.

• 한국분무공학회지
• /
• 제25권2호
• /
• pp.68-73
• /
• 2020

In the present study, experiments on the film boiling of liquid droplets on oxidized copper surface was conducted. The shape of pure water droplets was observed, and the evaporation rate of them was measured during the film boiling evaporation process. The droplet of initial volume 16 ~ 30 µl was applied onto the oxidized copper surface heated up to 300 ~ 500℃, then the shape of the droplet was analyzed during the film boiling evaporation. Experimental results showed that there was good correlation between dimensionless volume and dimensionless time. However, a significant difference in evaporation rate for small and large droplets discussed in previous study was not found.