Knowledge of the physical mechanisms governing bubble dynamics and two-phase heat transfer is critical in order to accurately predict and scale the performance of two-phase systems, most importantly in low-g environments. To better understand flow boiling, especially under microgravity conditions, the dynamics of single and multiple bubbles under different levels of bulk liquid velocity, surface orientation, contact angle, and substrate materials are studied in this work. Microfabricated cavities at the center of a flat heating surface are used to generate bubbles. Silicon and aluminum are used as substrate materials, with contact angles of 56° and 19°, respectively, with water as test liquid. The investigated bulk liquid velocities ranged from 0 m/s to 0.25 m/s, while surface orientation varies from horizontal to vertical, through 30°, 45° and 60°, and cavity spacing from 0.4 mm to 1.2 mm, in upflow conditions. Bulk liquid temperature was set close to saturation temperature, with bulk liquid subcooling less than 1° C, and wall superheat was maintained between 5.0° C and 6.0 °C. Based on the experimental data, a simple force balance model was developed, and is used to develop a model to predict bubble lift off. These forces are the lift force (F_b), the buoyancy force (F_b), the surface tension force (F_s), the contact pressure force (F_cp), and the inertia of both the vapor and the liquid displaced by the growing bubble. It is showed that at the instant when bubble lift off is initiated, the sum of forces acting on the bubble is equal to zero (and then becomes positive in the direction normal to the heater). This force balance is used to develop an expression for bubble lift off diameter. It also is found that for single and merged bubbles, when lift off occurs, buoyancy and lift forces are the only forces acting on the bubble, regardless of orientation, contact angle and flow velocity, and that for all cases, the ratio (F_b + F1) / A1 is constant and equal to 2.25 N/m2, where A1 is the bubble surface area at lift off.

This 2001 book provides a thorough review of the motion of bubbles and drops in reduced gravity.

This volume contains papers presented at the IUTAM Symposium on Bubble Dynamics and Interface Phenomena held at the University of Birmingham from 6-9 September 1993. In many respects it follows on a decade later from the very successful IUTAM Symposium held at CALTECH in June 1981 on the Mechanics and physics of bubbles in liquids which was organised by the late Milton Plesset and Leen van Wijngaarden. The intervening period has seen major development with both experiment and theory. On the experimental side there have been ad vances with very high speed photography and data recording that provide detailed information on fluid and interface motion. Major developments in both computer hardware and software have also led to extensive improvement in our understand ing of bubble and interface dynamics although development is still limited by the sheer complexity of the laminar and turbulent flow regimes often associated with bubbly flows. The symposium attracts wide and extensive interest from engineers, physical, chemical, biological and medical scientists and applied mathematicians. The sci entific committee sought to achieve a balance between theory and experiment over a range of fields in bubble dynamics and interface phenomena. It was our intention to emphasise both the breadth and recent developments in these various fields and to encourage cross-fertilisation of ideas on both experimental techniques and theo retical developments. The programme, and the proceedings recorded herein, cover bubble dynamics, sound and wave propagation, bubbles in flow, sonoluminescence, acoustic cavitation, underwater explosions, bursting bubbles and ESWL.

A Hamiltonian model for the radial and translational dynamics of clusters of coupled bubbles in an incompressible liquid developed by Ilinskii, Hamilton, and Zabolotskaya [J. Acoust. Soc. Am. 121, 786-795 (2007)] is extended to included the effects of compressibility in the host liquid. The bubbles are assumed to remain spherical and translation is allowed. The two principal effects of liquid compressibility are time delay in bubble interaction due to the finite sound speed and radiation damping due to energy lost to acoustic radiation. The incorporation of time delays produces a system of delay differential equations of motion instead of the system of ordinary differential equations in models of bubble interaction in an incompressible medium. The form of the Hamiltonian equations of motion is significantly different from the commonly used models based on Rayleigh-Plesset equations for coupled bubble dynamics, and it provides certain advantages in numerical integration of the time-delayed equations of motion. Corrections for radiation damping in clusters of interacting bubbles are developed in the form of a time-delayed expression for bubble self-action following the method of Ilinskii and Zabolotskaya [J. Acoust. Soc. Am. 92, 2837-2841 (1992)]. A set of approximate series expansions of this delayed expression is calculated to first order in the ratio of bubble radius to the characteristic wavelength of acoustic radiation from the bubble, and to varying orders in the ratio of bubble radius to characteristic bubble separation distance. Stability of the delay differential equations of motion is analyzed with four successive levels of approximation for the effects of radiation damping and time delay. The stability is analyzed with and without the effects of viscous and thermal damping. The effect of time delay and radiation damping on the pressure radiated by small systems of bubbles is considered. An approximate method to account for the delays in bubble interaction in a weakly compressible liquid is presented. This method converts the system of delay differential equations into an approximate system of ordinary differential equations, which may simplify numerical integration. Several sets of model equations incorporating propagation time delay in bubble interactions are solved numerically with existing algorithms specialized for delay differential equations. Numerical simulations of the dynamics of single bubbles, pairs of bubbles, and clusters of bubbles are used to compare the different levels of approximation for compressibility effects for low- and high-amplitude radial motion in systems of bubbles under free response and pulsed excitation by an external pressure source.