Exploratory Investigation of Thermally-Induced Water Flow in Soils

Michigan Technological University, Houghton MI

Investigators

Abstract

This project aims to answer a very fundamental yet very old scientific question: "Why and how does water move due to temperature gradients in porous materials?" This thermally induced water flux ubiquitously exists in porous materials, whenever both heat transfer and water movement are present. A scientific understanding of this phenomenon is an essential base for many important scientific and social challenges: climate effects on geomaterials, geothermal energy applications, behavior of porous materials under extreme conditions, and recovery of non-conventional fossil fuels such as gas hydrates and shale gas. However, despite the significance, this phenomenon has been an historically unsolved and perplexing issue affecting many science and engineering areas involving porous materials from traditional applications in civil engineering, soil science and petroleum engineering to emerging needs in microfluidics, material processing and biomechanics. This award supports the exploration of a new research concept/methodology and its application to reveal the physical mechanisms underlying thermally induced water flux for a complete scientific description and analysis framework for this phenomenon. As an exploratory study, which pioneers a very high-risk but possibly high-return concept, the success of the study may provide the geotechnical community a new understanding to tackle many issues which are hard to solve in the existing frameworks, and also provide a way to integrate porous material research which is currently distributed in various disciplines. In addition to supporting a doctoral student, the project will support outreach activities for rural, low-socioeconomic students and native tribal communities in the Upper Peninsula of Michigan. An annual summer program will be established to engage K-12 students in hands-on-learning for understanding of porous materials. This project will utilize a new concept/methodology, multiscale-driven multiphysics, to tackle the issue which appears difficult to solve with existing methods. The research will first focus on the macroscopic mechanisms underlying thermally induced water flux. For the purpose, thermally induced water flux will be related to the temperature dependence of the contact angle by conducting two sub-tasks: 1. measuring thermally induced water flux with a newly designed research setup, and 2. measuring the contact angle using a modified capillary rise method. Then molecular dynamics analysis will be carried out to reveal the microscopic mechanisms underneath the temperature dependence of the contact angle, which is hypothesized to be attributable to the temperature dependence of vapor adsorption. Finally, adsorption isotherms will be measured to experimentally validate the hypotheses and to couple the frameworks at both macro- and micro-scales, aiming at a physically-based and practically implementable framework for thermally induced water flux. The research is potentially very important as it attempts at breakthroughs via innovations on the theoretical (new theories at both macro and micro-scale), experimental (contact angle and thermally induced flux measurements), and numerical aspects (molecular simulations for water-mineral system). In the long term, the project also serves as an exploratory effort to examine the concept of multiscale-driven multiphysics, for the purpose of enabling solutions to critical historical issues and pressing challenges arising from upcoming applications in sustainability, energy and environmental protection, which more and more involve non-isothermal behavior of soils, and in a broad sense, multiphysics in porous materials.