Effects of reduced gravity on nucleate boiling bubble dynamics in saturated water

Abstract

A study was made of nucleate boiling bubble dynamics in saturated distilled water for various reduced gravity fields. The nucleation occurred on a very smooth horizontal nickel surface a t low heat fluxes. Since because of the smooth surface finish only a few nucleation sites were active, it was possible to photograph individual bubbles that were not interfered with by adjacent bubble columns. Data were taken a t seven different gravity fields in the range from 1.4 to 100% of earth gravity by placing the apparatus on a counterweighted falling platform. Measurements were made of bubble departure diameters and frequencies, growth rates, contact angles, base circle diameters, and rise velocities. Comparisons were made to determine whether the measured gravity dependence of these quantities was in agreement with that predicted by correlations in the literature.In the design of systems for space applications the effects of reduced gravity fields must often be considered. In an orbiting satellite or in space distant from planetary bodies the gravity field will closely approach zero. In a system that is accelerating slightly, or on bodies such as the moon, the gravity field will be a fraction of that on earth. Heat transfer processes such as pool boiling, condensation, and free convection are gravity dependent and hence would be expected to behave differently in reduced gravity fields. The effect of gravity has been indicated in numerous theoretical and experimental heat transfer correlations by the presence of a g factor. Although a number of experiments have been conducted to study highgravity effects (1 to 4 ) , there has been relatively little experimental work investigating the functional form of the g dependence in the reduced gravity range.The present paper is concerned with bubble dynamics for saturated pool boiling in reduced gravity fields in the range from 1.4 to 100% of earth gravity. A previous paper (5) , concerned mainly with burnout for low-gravity conditions, gives some information on bubble rise velocities and bubble diameters at departure for boiling water. It was found that the departure diameters increased as gWzf7 rather than g-1/2, as is commonly indicated in correlations such as the Fritz equation (reference 1 2 ) . In the present study an improved apparatus was used which permitted studies of bubble dynamics in greater detail.In (5) the nickel ribbon used as a test surface was generally quite crowded with nucleation sites, and bubbles probably interfered with each other. Consequently the diameters measured at bubble departure were likely not those of single bubbles grown from a single nucleation site without interference from adjacent bubbles. Also the nickel ribbon in ( 5 ) was only 0.2 in. wide, and hence the bubbles may have had a tendency to grow asymmetrically, that is elongated in the direction along the ribbon length. This would be especially true under reduced gravity conditions, where the bubbles can become quite large for boiling water.In the present apparatus boiling took place from a...

Bubble dynamics in nucleate pool boiling on micro-pin-finned surfaces in microgravity

“…In addition, five well-known theoretical correlations were employed to predict the bubble departure radius. By using this model, the results of the bubble departure radius on smooth surface were in good agreement with the experimental micro-g data of Siegel and Keshock [13], and the working fluid is saturated steam water in Siegel and Keshock's experiment. However, for high subcooled boiling (30e43 K), the liquid temperature near the heater surface is higher than that far away from the heater surface.…”

“…The bubble departure radius is almost constant though with changing gravitational acceleration. By using a force balance model, the bubble departure radius on smooth surface was estimated and compared with that from experimental measurements on literature in microgravity, conducted by Karri [16], and the results were in good agreement with the experimental micro-g data of Siegel and Keshock [13].…”

“…The effect of gravity on the bubble dynamics for saturated pool boiling of water and 60% sucrose have experimentally studied by Siegel and co-workers [13,14]. Meanwhile, bubble departure radii were measured.…”

Influence of heater thermal capacity on bubble dynamics and heat transfer in nucleate pool boiling

“…The numerical results of the present numerical method have been compared both with the experimental results of Siegel & Keshock [30] and with the numerical results of Son [9] and Son et al [10]. Good agreements were evident.…”

“…Furthermore, fused silica will be used as the substrate of an integrated heater in our on-going space experiment mission, SOBER-SJ10, which will be flown of our group, to study local convection and heat transfer around an isolated growing vapor bubble during nucleate pool boiling on a flat plate heater (Hu et al [31]). Nickel was used by Siegel & Keshock [30] in their experiments, and, as mentioned above, their experimental results were used to validate the present numerical method.…”