Effects of diameters and surface conditions of horizontal test cylinders on subcooled pool boiling CHFs with two mechanisms depending on subcooling and pressure

2002 ◽  
Author(s):  
Katsuya Fukuda ◽  
Akira Sakurai
Keyword(s):  
Pool Boiling ◽  
Surface Conditions

Parametric Study of Pool Boiling on Horizontal Highly Conductive Microporous Coated Surfaces

2007 ◽  
Vol 129 (11) ◽  
pp. 1465-1475 ◽  
Author(s):  
Chen Li ◽  
G. P. Peterson
Keyword(s):  
Coating Thickness ◽  
Copper Wire ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Experimental Investigations ◽  
Phase Flow ◽  
Porous Coatings ◽  
Surface Conditions ◽  
Porous Surfaces ◽  
Coated Surfaces

To better understand the mechanisms that govern the behavior of pool boiling on horizontal highly conductive microporous coated surfaces, a series of experimental investigations were designed to systematically examine the effects of the geometric dimensions (i.e., coating thickness, volumetric porosity, and pore size, as well as the surface conditions of the porous coatings) on the pool-boiling performance and characteristics. The study was conducted using saturated distilled water at atmospheric pressure (101kPa) and porous surfaces fabricated from sintered isotropic copper wire screens. For nucleate boiling on the microporous coated surfaces, two vapor ventilation modes were observed to exist: (i) upward and (ii) mainly from sideways leakage to the unsealed sides and partially from the center of porous surfaces. The ratio of the heater size to the coating thickness, the friction factor of the two-phase flow to single-phase flow inside the porous coatings, as well as the input heat flux all govern the vapor ventilation mode that occurs. In this investigation, the ratio of heater size to coating thickness varies from 3.5 to 38 in order to identify the effect of heater size on the boiling characteristics. The experimental results indicate that the boiling performance and characteristics are also strongly dependent on the volumetric porosity and mesh size, as well as the surface conditions when the heater size is given. Descriptions and discussion of the typical boiling characteristics; the progressive boiling process, from pool nucleate boiling to film boiling; and the boiling performance curves on conductive microporous coated surfaces are all systematically presented.

Nucleate Pool Boiling of Nitrogen With Different Surface Conditions

1968 ◽  
Vol 90 (4) ◽  
pp. 437-444 ◽  
Author(s):  
P. J. Marto ◽  
J. A. Moulson ◽  
M. D. Maynard
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Past History ◽  
Pool Boiling ◽  
Testing Procedure ◽  
Nucleate Boiling ◽  
Test Surface ◽  
Surface Conditions ◽  
Boiling Heat Transfer Coefficient ◽  
Teflon Coating

Pool-boiling heat transfer of liquid nitrogen from circular, 1-in.-dia horizontal disks was studied. Surface conditions included copper and nickel mirror finishes, and copper surfaces which were roughened, grease-coated, and Teflon-coated. Artificial cavities were manufactured, including mechanically drilled cylindrical holes of diameter 0.0043 and 0.015 in., and also a 0.022-in.-dia spark cut conical hole. Results indicate that a systematic testing procedure is necessary to obtain reproducible nucleate-boiling data. Surface roughness and surface material alter the nucleate-boiling curve. A grease coating significantly decreases the nucleate-boiling heat-transfer coefficient. A Teflon coating has very little effect. Past history of the test surface, including the length of time spent while boiling, can change boiling results. The effect of artificial cavities on both natural convection and nucleate-boiling was determined.

scholarly journals Effects of Surface Conditions on Nucleate Pool Boiling of Sodium

1966 ◽  
Vol 88 (2) ◽  
pp. 196-203 ◽  
Author(s):  
P. J. Marto ◽  
W. M. Rohsenow
Keyword(s):  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Boiling Curve ◽  
Porous Coatings ◽  
Surface Conditions ◽  
Effect Of Pressure ◽  
Pool Depth ◽  
Commercial Grade ◽  
Surface Finishes

Commercial grade sodium was boiled from a horizontal disk at pressures of 65 mm, 200 mm, and 400 mm Hg absolute, with sodium temperatures ranging from 1200 F to 1500 deg F. Heat fluxes as high as 236,000 Btu/hr sq ft were attained. Boiler surface finishes ranged from highly polished mirror finishes to coarse, porous coatings. By following a prescribed cleaning and filling procedure, nucleate-boiling results were generally reproducible for a given-type surface. The effect of roughness as well as any aging and hysteresis effects were experimentally determined. Incipient nucleate boiling results are discussed as well as the effect of pressure and pool depth on the nucleate-boiling curve.

Mechanisms of Subcooled Pool Boiling CHFS Depending on Subcooling, Pressure, and Test Heater Configurations and Surface Conditions in Liquids

2002 ◽  
Author(s):  
Akira Sakurai ◽  
Katsuya Fukuda
Keyword(s):  
Liquid Helium ◽  
Hydrodynamic Instability ◽  
Pool Boiling ◽  
Horizontal Cylinder ◽  
The Other ◽  
Cylinder Surface ◽  
Surface Conditions ◽  
Spontaneous Nucleation ◽  
Different Shapes ◽  
Horizontal Cylinders

The measured subcooled pool boiling CHFs on a horizontal cylinder heater for subcoolings with pressures as a parameter in water, liquid nitrogen, liquid helium etc. were previously well described by the subcooled pool boiling CHF correlations newly derived assuming two different CHF mechanisms resulting from hydrodynamic instability (HI) and heterogeneous spontaneous nucleation in originally flooded cavities (HSN): the CHFs for lower subcoolings which depend on pressure, and the CHFs for higher subcoolings which were almost independent of pressure in water extremely disagreed with corresponding values derived from existing subcooled pool boiling CHF correlations only based on hydrodynamic instability except the CHFs near saturated condition. In the present paper, to begin with the effect of heater configuration on the CHFs resulting from the HI and the HSN were clarified using the existing CHF data measured for the horizontal cylinders with diameters ranging from 0.2 to 5.84 mm, and the test ribbon heaters with different shapes for subcoolings ranging from zero to about 160 K at pressures ranging from 0.013 to 2 MPa in water and ethanol etc., and next the effects of horizontal cylinder surface conditions on the CHFs resulting from the HI and the HSN were clarified using the CHF data measured by the authors for 1.2 mm-diam. platinum horizontal cylinders with commercial, rough and mirror surfaces (CS, RS and MS) in water for the wide ranges of subcooling and pressure. The CHFs for subcoolings at a pressure measured using a horizontal cylinder, first increased up to the maximum CHF, secondly decreased down to the minimum CHF, and finally again increased monotonously with an increase in subcooling as a typical trend; namely the CHFs were divided into three groups of first, second and third ones for low, middle (transition) and high subcoolings respectively. However, the CHFs for middle subcoolings became insignificant, and the CHFs resulting from the HI or the HSN for all subcoolings including zero occurred depending on pressure, heater configuration, its surface conditions and a kind of liquid. The effect of cylinder diameters on the coefficients in the two CHF correlations representing CHFs resulting from the HI and the HSN previously presented were clarified in the liquids. It was confirmed that there existed the CHFs resulting from the HI measured for the horizontal cylinders with CS, RS and MS at lower pressures for lower subcoolings; the CHFs almost agreed with one another at the same subcooling independently of the surface conditions, though the CHFs resulting from the HSN for the MS cylinder were extremely lower corresponding CHFs for CS and RS cylinder at higher pressures. It should be noted that the CHFs resulting from the HSN predominated and on the other hand the CHF resulting from the HI existed in extremely narrow regions in a large number of the CHF data measured for the wide ranges of the conditions not only in wetting liquids but also in water.

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