Creare Engineering Services – Spacecraft Void Fraction Meter

Spacecraft Void Fraction Meter Creare has developed a void fraction meter capable of characterizing two-phase flow behavior of fluids with high-density vapor phases under microgravity conditions. Vapor/liquid two-phase flow regimes have been well characterized at normal Earth gravity, and in microgravity situations using air and water, but much remains to be learned. In the past, NASA has relied upon single-phase, liquid-ammonia cooling systems for spacecraft heat dissipation, but the reduced system mass possible with two-phase systems fuels the need to better understand two-phase flow behaviors in space. Up to now, obtaining quantified void fraction information has dictated undertaking simulations using water and air at low fluid/gas densities. However, the larger gas densities encountered using ammonia systems leave legitimate questions unanswered about slug formation and annular flow behavior that may not be accurately addressed by the application of unqualified scaling functions.

Several prototype instruments were built at various sizes. Instruments at 12.7 mm ID were installed in an existing two-phase flow test facility managed by Texas A&M University. Creare engineers then performed extensive experiments aboard NASA’s KC-135 aircraft, during 11 flights, experiencing approximately 400 parabolic arcs, to produce limited periods of reduced gravity.

Creare obtained detailed void fraction, liquid film thickness, pressure drop, and flow rate measurements; investigated the annular flow regime, the slug flow regime, and the transition between them at over 100 microgravity test conditions; and examined and characterized the scaling of multi-phase behavior through analysis of data, comparison with mechanistic analytical models, and comparison with previously obtained data. The results extend our knowledge of fluid behavior in space and should enable the confident design of multiphase cooling systems for microgravity environments.