scholarly journals Film Boiling on Downward Quenching Hemisphere of Varying Sizes

Author(s):  
Chan S. Kim ◽  
Kune Y. Suh ◽  
Joy L. Rempe ◽  
Fan-Bill Cheung ◽  
Sang B. Kim

Film boiling heat transfer coefficients for a downward-facing hemispherical surface are measured from the quenching tests in DELTA (Downward-boiling Experimental Laminar Transition Apparatus). Two test sections are made of copper to maintain low Biot numbers. The outer diameters of the hemispheres are 120 mm and 294 mm, respectively. The thickness of all the test sections is 30 mm. The effect of diameter on film boiling heat transfer is quantified utilizing results obtained from the test sections. The measured data are compared with the numerical predictions from laminar film boiling analysis. The measured heat transfer coefficients are found to be greater than those predicted by the conventional laminar flow theory on account of the interfacial wavy motion incurred by the Helmholtz instability. Incorporation of the wavy motion model considerably improves the agreement between the experimental and numerical results in terms of heat transfer coefficient. In addition, the interfacial wavy motion and the quenching process are visualized through a digital camera.

2004 ◽  
Vol 120 ◽  
pp. 269-276
Author(s):  
M. Maniruzzaman ◽  
R. D. Sisson

Quenching heat treatment in a liquid medium is a very complex heat transfer process. Heat extraction from the part surface occurs through several different heat transfer mechanisms in distinct temperature ranges, namely, film boiling, partial film boiling (i.e. transition), nucleate boiling and convection. The maximum heat transfer occurs during the nucleate boiling stage. Experimental study shows that, the effective surface heat transfer coefficient varies more than two orders of magnitude with the temperature during the quenching. For quenching process simulation, accurate prediction of the time-temperature history and microstructure evolution within the part largely depends on the accuracy of the boundary condition supplied. The heat transfer coefficient is the most important boundary condition for process simulation. This study focuses on creating a database of heat transfer coefficients for various liquid quenchant-metallic alloy combinations through experimentation using three different quench probes. This database is a web-based tool for use in quench process simulation. It provides at-a-glance information for quick and easy analysis and sets the stage for a Decision Support System (DSS) and Data Mining for heat-treating process.


2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Chan Soo Kim ◽  
Kune Y. Suh

The effect of inclination angle of the downward facing flat plate on the interfacial wavy motion is investigated utilizing the water quenching test apparatus downward ebullient laminar transition apparatus flat surface (DELTA-FS) in a quasi-steady state. Film boiling heat transfer coefficients are obtained on the relatively long surface in the flow direction. Interfacial velocities at the various inclination angles and wall superheat conditions are determined through the analysis of the visualized continuous snapshots with 1000 fps. Visualization of the vapor film reveals that the interfacial wavelength increases and the interfacial velocity decreases as the flat plate moves from the vertical to downward facing locations. A new semi-empirical correlation is developed from the measured heat transfer coefficients and interfacial velocities. The correlation shows good agreement with the previous water test results on vertical plates. In the case of the previous other fluid experimental results on the vertical plates, the correlation overpredicts the film boiling heat transfer coefficients at the experimental condition.


1966 ◽  
Vol 88 (1) ◽  
pp. 17-23 ◽  
Author(s):  
C. A. Heath ◽  
C. P. Costello

Ethanol, pentane, and Freon-113 were tested for atmospheric pressure, saturated film-boiling characteristics. Turbulent waves arise close to the bottom of vertical platinum plates and the data become identical to those obtained with horizontal plates, verifying an earlier contention by Y. P. Chang. The equation of Berenson fits the data for both horizontal and vertical heaters fairly well if modified for geometry, and the equation also correctly predicts the effect of acceleration on film-boiling heat-transfer coefficients. At high temperature differences, Berenson’s equation for the heat-transfer coefficient is slightly conservative, which is qualitatively predictable by analyzing the departures of the actual system from the idealized model of Berenson.


2004 ◽  
Vol 120 ◽  
pp. 521-528
Author(s):  
M. Maniruzzaman ◽  
R. D. Sisson

Quenching heat treatment in a liquid medium is a very complex heat transfer process. Heat extraction from the part surface occurs through several different heat transfer mechanisms in distinct temperature ranges, namely, film boiling, partial film boiling (i.e. transition), nucleate boiling and convection. The maximum heat transfer occurs during the nucleate boiling stage. Experimental study shows that, the effective surface heat transfer coefficient varies more than two orders of magnitude with the temperature during the quenching. For quenching process simulation, accurate prediction of the time-temperature history and microstructure evolution within the part largely depends on the accuracy of the boundary condition supplied. The heat transfer coefficient is the most important boundary condition for process simulation. This study focuses on creating a database of heat transfer coefficients for various liquid quenchant-metallic alloy combinations through experimentation using three different quench probes. This database is a web-based tool for use in quench process simulation. It provides at-a-glance information for quick and easy analysis and sets the stage for a Decision Support System (DSS) and Data Mining for heat-treating process.


1964 ◽  
Vol 86 (1) ◽  
pp. 81-87 ◽  
Author(s):  
E. E. Polomik ◽  
S. Levy ◽  
S. G. Sawochka

Film boiling heat-transfer coefficients, beyond “burnout,” of 800–2000 Btu/hr ft2 deg F, were measured with steam-water mixtures in annular flow at pressures of 800, 1100, and 1400 psi with healer temperatures not exceeding 1000 deg F. Variation of co-efficients with pressure, mass velocity, and steam quality are presented together with a correlation in the range of parameters studied.


Author(s):  
Qiusheng Liu ◽  
Masahiro Shiotsu ◽  
Akira Sakurai ◽  
Katsuya Fukuda

Forced convection film boiling heat transfer from a horizontal cylinder in water and Freon-113 flowing upward perpendicular to the cylinder under subcooled conditions was measured for the flow velocities from 0 to 1 m/s at the system pressures ranging from 100 to 500 kPa: the platinum horizontal cylinders with diameters ranging from 0.7 to 5 mm were used as the test heaters. The film boiling heat transfer coefficients were obtained for the surface superheats from about 800 K for water and from about 400 K for Freon-113 down to minimum film boiling surface superheats. These heat transfer coefficients increase with the increase in flow velocity, liquid subcooling, system pressure, and with the decrease in cylinder diameter. A correlation for subcooled forced convection film boiling heat transfer was presented, which can describe the experimental data obtained within ±20% for the flow velocities below 0.7 m/s, and within −30% to +20% for the higher flow velocities. The correlation also predicted well the data by Shigechi (1983), Motte and Bromley (1957), and Sankaran and Witte (1990) obtained for the larger diameter cylinders and higher flow velocities in various liquids at the pressures of near atmospheric. The Shigechi’s data were in the range from about −20% to +15%, the data of Motte and Bromley were about ±30%, and the data of Sankaran and Witte were within +20% of the curves given by the corresponding predicted values.


2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Jinsub Kim ◽  
Seongchul Jun ◽  
Jungho Lee ◽  
Juan Godinez ◽  
Seung M. You

The effect of surface roughness on the pool boiling heat transfer of water was investigated on superhydrophilic aluminum surfaces. The formation of nanoscale protrusions on the aluminum surface was confirmed after immersing it in boiling water, which modified surface wettability to form a superhydrophilic surface. The effect of surface roughness was examined at different average roughness (Ra) values ranging from 0.11 to 2.93 μm. The boiling heat transfer coefficients increased with an increase in roughness owing to the increased number of cavities. However, the superhydrophilic aluminum surfaces exhibited degradation of the heat transfer coefficients when compared with copper surfaces owing to the flooding of promising cavities. The superhydrophilic aluminum surfaces exhibited a higher critical heat flux (CHF) than the copper surfaces. The CHF was 1650 kW/m2 for Ra = 0.11 μm, and it increased to 2150 kW/m2 for Ra = 0.35 μm. Surface roughness is considered to affect CHF as it improves the capillary wicking on the superhydrophilic surface. However, further increase in surface roughness above 0.35 μm did not augment the CHF, even at Ra = 2.93 μm. This upper limit of the CHF appears to result from the hydrodynamic limit on the superhydrophilic surface, because the roughest surface with Ra = 2.93 μm still showed a faster liquid spreading speed.


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