The international space station packed bed reactor experiment: capillary effects in gas-liquid two-phase flows.

Experimental data on flow patterns and pressure drop in two-phase gas-liquid flows through a packed bed obtained aboard the International Space Station (ISS) are analyzed in the limit of low flow rates. Four distinct flow regimes (dispersed bubble, pulse, elongated or large bubble, and gas continuous) are observed and the transition boundaries are identified by a change in the slope of the pressure gradient versus flow rate. It is found that the pressure drop is a function of flow history with the relative magnitude of the hysteresis decreasing with increasing gas or liquid flow rates.

Experimental investigation of frequency and amplitude of density wave oscillations in vertical upflow boiling.

Historically, study of two-phase flow instabilities has been arguably one of the most challenging endeavors in heat transfer literature due to the wide range of instabilities systems can manifest depending on differences in operating conditions and flow geometry. This study utilizes experimental results for vertical upflow boiling of FC-72 in a rectangular channel with finite inlet quality to investigate Density Wave Oscillations (DWOs) and assess their potential impact on design of two-phase systems for future space missions. High-speed flow visualization image sequences are presented and used to directly relate the cyclical passage of High and Low Density Fronts (HDFs and LDFs) to dominant low-frequency oscillations present in transient pressure signals commonly attributed to DWOs.

Flow condensation pressure oscillations at different orientations.

Investigation of two-phase flow dynamic behavior and instabilities has traditionally centered on phenomena present in boiling flows due to the safety critical nature of boiling in a variety of cooling applications. Analysis of pressure signals in condensing systems reveal the presence of relevant oscillatory phenomena during flow condensation as well, which may impact performance in applications concerned with precise system control. Towards this end, the present study presents results for oscillatory behavior observed in pressure measurements during flow condensation of FC-72 in a smooth circular tube in vertical upflow, vertical downflow, and horizontal flow orientations.

Experimental investigation into the impact of density wave oscillations on flow boiling system dynamic behavior and stability.

In order to better understand and quantify the effect of instabilities in systems utilizing flow boiling heat transfer, the present study explores dynamic results for pressure drop, mass velocity, thermodynamic equilibrium quality, and heated wall temperature to ascertain and analyze the dominant modes in which they oscillate. Flow boiling experiments are conducted for a range of mass velocities with both subcooled and saturated inlet conditions in vertical upflow, vertical downflow, and horizontal flow orientations. High frequency pressure measurements are used to investigate the influence of individual flow loop components (flow boiling module, pump, pre-heater, condenser, ) on dynamic behavior of the fluid, with fast Fourier transforms of the same used to provide critical frequency domain information.