Altering Bubble Dynamics via Vapor Extraction

Abstract

Bubble dynamics in the presence of a porous confining surface through which vapor is extracted was experimentally investigated. Using a pulsed laser operating at 3500 pulses per second (pps), bubbles were generated at a single, 30 μm diameter nucleation site in a silicon disk. A time-averaged heat flux of 80 W/cm2 and a constant pressure differential of 35 kPa across a porous surface were maintained. The surface, a supported porous Teflon® membrane, has a nominal porosity of 55% and pore diameter of 0.45μm. Steady-state heating was achieved as determined from a one-dimensional conduction model yielding a dimensionless surface temperature fluctuations of less than 0.01%. Bubble diameter and frequency were determined using high-speed imaging for ten gap heights ranging between 0.52 mm and 3.99 mm, where the gap height is defined as the distance between the heated surface and the confining surface. Bubble dynamics of freely departing, coalescing, and rupturing bubbles are considered. Results are compared to diameters and frequencies achieved in unconfined (i.e. pool boiling) conditions. Isolated bubble dynamics depend on gap height and can be grouped into three ranges: greater than, equal to, and less than the bubble diameters for unconfined conditions, which for the present conditions is 1.53 mm. This paper is a work in progress.

Altering Bubble Dynamics via In Situ Vapor Extraction

“…The laser spot size used for this study was 1.21 mm diameter, with 0.93 W delivered to the bottom of the silicon surface using a 3500 Hz laser pulse frequency. It was shown by Fox et al [16] that these conditions resulted in a steady temperature at the top of the silicon surface to within 0.01% of the surface excess temperature during boiling.…”

“…through(16) are the following: (i) growth rate, (ii) diameter (volume) of the bubble at rupture, which is used to indicate the onset of Regime II, (iii) the diameter of the extraction area during Regime II, which is expected to vary over time and start at a value of zero at the point of rupture, (iv) the bubble departure diameter (volume), used to indicate when to turn off growth at the onset of Regime III, and (v) the diameter of the extraction area during Regime III.The growth rate for the diabatic case is simply the volumetric injection rate of the air, the averaged value of which is 88.1 mm 3 /s. For these initial stages of model development, the correlation provided by Eq.…”