Harvesting Water from Icing Porous Media for In-situ Resource Utilization

Abstract

Water is one of the most basic needs in our daily life everywhere, whether in our homes, workplaces, vacations, etc. However, when it comes to space missions, extracting water from the ground for human habitation is very expensive. According to NASA, it costs $25000 for a space shuttle cargo to bring 1 gallon of water to space. Towards the space sustainability, it is imperative to harvest water from space by taking advantage of solar energy. In fact, ice exists in extraterrestrial regolith, and its in-situ resource utilization is very attractive though no technological solution is available yet. To tackle such water extraction challenge, the knowledge of ice melting dynamics in porous media comes first. Systematic characterization is required to understand the transient ice melting process in porous media like moon regolith. For icing porous media, it is very complex to study the ice-water phase transition and movement of the interface within pore-throat network. Unlike bulk volume, the solid-liquid interface has an extremely irregular shape due to porous matrix, making it difficult to monitor the interface motion. In addition, it is impossible to photograph the interface position, and observe the flow structure in the melt region due to opaque nature of porous media. The complicated 3D pore-throat network also adds complexity to the problem. As a result, it is difficult to capture the transient phase distribution and understand the effect of the grain size on the melting process. Fortunately, the advent of technologically modern tools such as nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are paving the way to probe physical insights without destroying opaque materials’ structure or disturbing phase transition processes.

In this thesis, the ice melting dynamics, particularly ice-water phase transition, in porous media is experimentally characterized by using the low-field NMR analyzer along with thermocouples. The porous samples contain homogeneously packed soda lime glass beads or heterogeneously distributed regolith simulants with vertical and horizontal orientations. The main outcome of the NMR experiment is the transversal relaxation time (𝑇2 ) curve, where the peak area values are used to determine the transient volume of water and melting rate of icing porous media. The peak area is the total area under the 𝑇2 curve, which represents the instantaneous amount of water. The temperature distribution is also extracted from the thermocouple experiments. Three 𝑇2 times are obtained from the 𝑇2 curve, and these are 𝑇2 min, 𝑇2 max, and 𝑇2 peak. In the horizontal orientation, all 𝑇2 values are shifted towards longer time, indicating that melting is initiated in the smaller pores and proceeds at a relatively faster rate as compared to larger glass beads. These NMR results are in agreement with the thermocouple results. Further analysis via Gibbs Thomson equation shows the confinement effect is important in micro-sized porous media as it shifts the thermodynamic phase-change equilibrium. In the vertical orientation, thermocouple results indicate that melting rate is larger in the larger glass beads than in smaller glass beads, mainly because of the considerable permeability difference aided by the gravity effect. This is further confirmed by analytical calculation of permeability based on the Carman-Kozeny equation. Overall, confinement effect and permeability play a key role in the horizontal and vertical orientation, respectively. Moreover, MRI also provides the distribution of the water content in porous media with a stack of cross-section images.

Date of Award	Aug 2023
Original language	American English
Supervisor	TJ Zhang (Supervisor)