NASA Lewis Research Center low-gravity fluid management technology program

A history of the Lewis Research Center in space fluid management technology program is presented. Current programs which include numerical modeling of fluid systems, heat exchanger/radiator concept studies, and the design of the Cryogenic Fluid Management Facility are discussed. Recent analytical and experimental activities performed to support the Shuttle/Centaur development activity are highlighted

Nonlinear Effects in Cavitation Cloud Dynamics

This paper presents a spectral analysis of the response of a fluid containing bubbles to the motions of a wall oscillating normal to itself. First, a fourier series analysis of the Rayleigh-Plesset equation is used to obtain an approximate solution for the nonlinear effects in the oscillations of a single bubble. This is used in the approximate solution of the oscillating wall problem and the resulting expressions are evaluated numerically in order to examine the nonlinear effects. The frequency content of the bubble radius and pressure oscillations near the wall is examined. Nonlinear effects are seen to increase with increased amplitude of wall oscillation, reduced void fraction and viscous and surface tension effects

Simple improvements to classical bubble nucleation models

We revisit classical nucleation theory (CNT) for the homogeneous bubble nucleation rate and improve the classical formula using a new prefactor in the nucleation rate. Most of the previous theoretical studies have used the constant prefactor determined by the bubble growth due to the evaporation process from the bubble surface. However, the growth of bubbles is also regulated by the thermal conduction, the viscosity, and the inertia of liquid motion. These effects can decrease the prefactor significantly, especially when the liquid pressure is much smaller than the equilibrium one. The deviation in the nucleation rate between the improved formula and the CNT can be as large as several orders of magnitude. Our improved, accurate prefactor and recent advances in molecular dynamics simulations and laboratory experiments for argon bubble nucleation enable us to precisely constrain the free energy barrier for bubble nucleation. Assuming the correction to the CNT free energy is of the functional form suggested by Tolman, the precise evaluations of the free energy barriers suggest the Tolman length is $\simeq 0.3 \sigma$ independently of the temperature for argon bubble nucleation, where $\sigma$ is the unit length of the Lenard-Jones potential. With this Tolman correction and our new prefactor one gets accurate bubble nucleation rate predictions in the parameter range probed by current experiments and molecular dynamics simulations.Comment: 10pages, 6figures, Accepted for publication in Physical Review