Gas–liquid flows through porous media in microgravity: The International Space Station Packed Bed Reactor Experiment

Abstract

Experimental results on pressure drop and flow patterns for gas–liquid flow through packed beds obtained in the International Space Station with two types of packing are presented and analyzed. It is found that the pressure drop depends on the packing wettability in the viscous–capillary (V–C) regime and this dependence is compared with previously published results developed using short duration low‐gravity aircraft tests. Within the V–C regime, the capillary contribution is the dominant force contributing to the pressure drop for the wetting case (glass) versus the viscous contribution dominating for the non‐wetting case (Teflon). Outside of the V–C regime, it is also found that hysteresis effects that are often strong in normal gravity gas–liquid flows are greatly diminished in microgravity and pressure drop is nearly independent of packing wettability. A flow pattern transition map from bubble to pulse flow is also compared with the earlier aircraft data.

Bubble Morphology Analysis and Pressure Drop of Gas–Liquid Two-Phase Flow inside a Quarto Static Mixer

“…The flow patterns are discriminated by standard deviation, kurtosis, skewness, and domain frequency. Different pressure fluctuation sources are distinguished based on statistical analysis. − …”

Hydrodynamics of bubble flow through a porous medium with applications to packed bed reactors

“…Experiments on gas-liquid flow through a packed-bed reactor performed under microgravity conditions at the International Space Station showed the presence of the so-called bubble and pulse flow regimes but noted the absence of the so-called trickle and spray flow regimes. [9][10][11] They found that the flow regime maps in microgravity differ from those under terrestrial gravity conditions, leaving a knowledge gap regarding the understanding of how gravity shapes the presence (or absence) of regimes in gas-liquid flow through a porous medium. High-fidelity simulations can bridge this gap.…”

“…We did not consider the effect of wettability in the present study, so contact angle dynamics were not modeled. We expect that the influence of the contact angle on flow dynamics is negligible in liquid continuous flow regimes, such as the bubble flow studied in this article 9 . In Section 3.3, unless otherwise stated, microgravity conditions () are considered in the simulations.…”

“…They observed larger pressure drops in microgravity, which they attributed to the dominance of capillary forces in microgravity conditions. Further work in the viscous‐capillary regime (i.e., negligible flow inertia) at microgravity was conducted by Motil et al 9 for both wetting and nonwetting packing materials. They found that the capillary contribution dominates the overall pressure drop in the wetting case, while the viscous contribution is dominant for the nonwetting case.…”

“…Overall, these prior works on the hydrodynamics of gas‐liquid flow through a PBR under microgravity (or microgravity‐like) conditions broadly focused on flow regime characterization (into a bubble or pulse flow) and the corresponding pressure drops, without gaining insight into the bubble dynamics. Moreover, in the recent analysis of the microgravity experiments on the ISS, Motil et al 9 noted that “one fundamental problem identified in the PBRE, that is, there is a minimum liquid superficial flux needed to dislodge trapped bubbles in a porous medium.” To better understand this fundamental problem and thus fill a knowledge gap in the literature, we explore the bubble flow regime in depth by investigating the influence of inertia, capillary, and buoyancy forces on a bubble's entrapment and displacement through a PBR. To this end, we propose new dynamic scales to estimate the pore‐scale force magnitudes and balances on a bubble traversing a PBR, which improves on the assumption of previous studies 9–11 that the dimensionless numbers should be defined based on a constant packing diameter, without taking into consideration the scales characterizing the tortuous paths through the PBR.…”