Subcooled Pool Boiling in Variable Gravity Environments

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Rishi Raj ◽  
Jungho Kim ◽  
John McQuillen
Keyword(s):  
Heat Transfer ◽  
Pool Boiling ◽  
Gravity Level ◽  
Dissolved Gas ◽  
Subcooled Liquid ◽  
Size Dependent ◽  
Gravity Effects ◽  
Parametric Effects ◽  
Bubble Growth And Departure ◽  
Continuous Range

Virtually all data to date regarding parametric effects of gravity on pool boiling have been inferred from experiments performed in low-g, 1g, or 1.8g conditions. The current work is based on observations of boiling heat transfer obtained over a continuous range of gravity levels (0g–1.8g) under subcooled liquid conditions (n-perfluorohexane, ΔTsub=26°C, and 1 atm), two gas concentrations (220 ppm and 1216 ppm), and three heater sizes (full heater-7×7 mm2, half heater-7×3.5 mm2, and quarter heater-3.5×3.5 mm2). As the gravity level changed, a sharp transition in the heat transfer mechanism was observed at a threshold gravity level. Below this threshold (low-g regime), a nondeparting primary bubble governed the heat transfer and the effect of residual gravity was small. Above this threshold (high-g regime), bubble growth and departure dominated the heat transfer and gravity effects became more important. An increase in noncondensable dissolved gas concentration shifted the threshold gravity level to lower accelerations. Heat flux was found to be heater size dependent only in the low-g regime.

Gravity Scaling Parameter for Pool Boiling Heat Transfer

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Rishi Raj ◽  
Jungho Kim ◽  
John McQuillen
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Gravity Level ◽  
Dissolved Gas ◽  
Experimental Conditions ◽  
Scaling Parameter ◽  
Flux Data ◽  
Earth Gravity ◽  
Variable Gravity ◽  
Continuous Range

Although the effects of microgravity, earth gravity, and hypergravity (>1.5 g) on pool boiling heat flux have been studied previously, pool boiling heat flux data over a continuous range of gravity levels (0–1.7 g) was unavailable until recently. The current work uses the results of a variable gravity, subcooled pool boiling experiment to develop a gravity scaling parameter for n-perfluorohexane/FC-72 in the buoyancy-dominated boiling regime (Lh/Lc>2.1). The heat flux prediction was then validated using heat flux data at different subcoolings and dissolved gas concentrations. The scaling parameter can be used as a tool to predict boiling heat flux at any gravity level in the buoyancy dominated regime if the data under similar experimental conditions are available at any other gravity level.

On the Heat Transfer Characteristics of a Single Bubble Growth and Departure During Pool Boiling

2016 ◽  
Author(s):  
Mostafa Mobli ◽  
Chen Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Bubble Growth ◽  
Pool Boiling ◽  
Vof Method ◽  
Physical Relationship ◽  
Interface Diffusion ◽  
Departure Time ◽  
Parasitic Currents ◽  
Bubble Growth And Departure

In the present study, bubble growth and departure characteristics during saturated pool boiling were investigated numerically, and a comprehensive model was proposed and developed to study the heat transfer during growth and departure of a bubble as well as bubble growth rate and departure time. Two-phase characteristics of the boiling phenomena can be captured by well-known Volume of Fluid (VOF) method. However, the VOF method is susceptible to parasitic currents because of approximate interface curvature estimations. Thus, sharp surface formula (SSF) method was employed to effectively eliminate the presence of the parasitic currents. VOF method is a volume capturing method and hence, may be subject to interface diffusion, due to the fact that interface is smeared through some number of computational cells. Interface compression scheme is applied to prevent the plausible interface diffusion of the VOF method. To avoid unrealistic temperature profiles at the solid-liquid surface, a conjugate heat transfer model was used to calculate the heat flux going into the liquid region from the heater through the solution of conduction equation in solids. Phase change at the interface was incorporated based on Hardt and Wondra’s model in which source terms are derived from a physical relationship for the evaporation mass flux. Furthermore, effects of micro region heat transfer on the departure time of the bubble was investigated. Micro region heat transfer was included in the model by solving a temporal evolution equation and incorporating the resulting heat flux in the tri-phase contact line. In this study, OpenFOAM package was used to investigate the characteristics of the bubble growth and departure as well as the wall heat flux. The model was benchmarked by comparing the simulation results to available experimental and numerical literatures, as well as analytical solutions.

Effects of Dissolved Gas Content on Pool Boiling of a Highly Wetting Fluid

1995 ◽  
Vol 117 (3) ◽  
pp. 687-692 ◽  
Author(s):  
S. M. You ◽  
T. W. Simon ◽  
A. Bar-Cohen ◽  
Y. S. Hong
Keyword(s):  
Heat Transfer ◽  
Pool Boiling ◽  
Electronics Cooling ◽  
Horizontal Cylinder ◽  
Gas Content ◽  
Free Fluid ◽  
Dissolved Gas ◽  
Boiling Incipience ◽  
Wetting Fluid

Experimental results on pool boiling heat transfer from a horizontal cylinder in an electronic cooling fluid (FC-72) are presented. The effects on the boiling curve of having air dissolved in the fluid are documented, showing that fluid in the vicinity of the heating element is apparently liberated of dissolved gas during boiling. Dissolved gas was found to influence boiling incipience only with high gas concentrations (>0.005 moles/mole). For low-to-moderate concentrations, a larger superheat is required to initiate boiling and a hysteresis is observed between boiling curves taken with increasing and decreasing heat flux steps. Boiling, a very effective mode of heat transfer, is attractive for electronics cooling. The present experiment provides further documentation of the role of dissolved gas on the incipience process and shows similarities with subcooled boiling of a gas-free fluid.

Gravity Scaling Parameter for Pool Boiling Heat Transfer

2009 ◽  
Author(s):  
Rishi Raj ◽  
Jungho Kim ◽  
John McQuillen
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Gravity Level ◽  
Low Gravity ◽  
Experimental Conditions ◽  
Scaling Parameter ◽  
Flux Data ◽  
Variable Gravity ◽  
Continuous Range ◽  
Good Agreement

The effect of low gravity on pool boiling heat flux has been studied by researchers, but pool boiling heat flux data over a continuous range of gravity levels (0g–1.8g) was unavailable until recently. The current work uses the results of a variable gravity subcooled pool boiling experiment to develop a gravity scaling parameter for prediction purposes. The heat flux prediction at various gravity levels was found to be in good agreement with the measured heat flux data. The scaling parameter can be used as a tool to predict boiling heat flux at any gravity level if the data under similar experimental conditions are available at any other gravity level. The scaling parameter has been demonstrated to be valid for pool boiling of n-perfluorohexane in heater size independent boiling regime (Lh/Lc>2.8).

Gas-Saturated Pool Boiling Heat Transfer From Smooth and Microporous Surfaces in FC-72

1996 ◽  
Vol 118 (3) ◽  
pp. 662-667 ◽  
Author(s):  
J. P. O’Connor ◽  
S. M. You ◽  
J. Y. Chang
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Smooth Surface ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Pure Liquid ◽  
Dissolved Gas ◽  
Pool Boiling Heat Transfer ◽  
Boiling Process ◽  
Transfer Mechanisms

The effects of surface treatments and “gassy-subcooling” on pool boiling heat transfer are quantified by testing both smooth and treated surfaces at gassy-subcooling levels from O°C to 40°C (1 atm) and 40°C to 85°C (3 atm). Incipient and nucleate boiling wall superheats decrease over this range of gassy-subcooling. At gassy-subcooling levels greater than 20°C, the boiling curves for the smooth surface indicate two distinct regions governed by different heat transfer mechanisms, one in which the boiling process is influenced by the presence of dissolved gas, the other by boiling of the pure liquid. The critical heat flux (CHF) for each surface continually increases with increased levels of gassy-subcooling and the CHF sensitivity to gassy-subcooling is higher for the treated surface. The CHF increase due to combined surface treatment and gassy-subcooling (85°C) is ~400 percent (78 W/cm2).

Measurement of Temperatures Associated With Bubbles in Subcooled Pool Boiling

1969 ◽  
Vol 91 (1) ◽  
pp. 123-128 ◽  
Author(s):  
J. D. Jacobs ◽  
A. H. Shade
Keyword(s):  
Heat Transfer ◽  
Carbon Tetrachloride ◽  
Heat Source ◽  
Optical System ◽  
High Speed ◽  
Pool Boiling ◽  
Motion Pictures ◽  
Heater Surface ◽  
Subcooled Liquid ◽  
Idealized Model

High-speed motion pictures were taken of initial pool boiling of carbon tetrachloride using a schlieren optical system and associated temperature instrumentation. Many bubbles leaving the heat source were found to be superheated regardless of the degree of subcooling of the liquid. Individual bubbles rising from the heater surface carried a thin laminar layer of hot liquid on their upper surface and trailed a wake of warm liquid. An idealized model of the surrounding warm liquid was empirically developed and accounts for a significant portion of the heat transfer in pool boiling of highly subcooled liquid.

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