Water scarcity is a particularly severe challenge in arid and desert climates. While a substantial amount of water is present in the form of vapor in the atmosphere, harvesting this water by state- of-the-art dewing technology can be extremely energy intensive and impractical, particularly when the relative humidity (RH) and/or temperature are low. In contrast, atmospheric water harvesters (AWHs) that utilize sorbents enable capture of vapor at low RH conditions and can be driven by the abundant source of solar-thermal energy, and consequently exhibit higher efficiency even at low RH conditions. Metal organic frameworks (MOFs) are particularly attractive as an adsorbent for this application because they can capture more water and require lower regeneration temperatures for its release compared to conventional sorbents (zeolites, silica gels, etc.). Much of the recent materials development has focused on a single material metric, equilibrium vapor uptake in the material (kg of water uptake/kg of dry adsorbent), as found from the adsorption isotherm. This equilibrium property, however, is not alone a good indicator of the actual performance of the AWH system. Understanding material properties which affect heat and mass transport are equally important in the development of materials and components for AWH, because resistances associated with heat and mass transport in the bulk material dramatically change the system performance. This talk will first outline the detailed experimental measurements required to understand the transport properties at the material level and a theoretical framework which can connect mass transport all the way to the system scale. The framework considers diffusion both inside a single crystal as well as macro-scale geometric<br/>parameters, such as the thickness of the adsorbent layer. System level design implications will also be discussed.

Understanding material and component level properties on the performance of MOF-based atmospheric water harvesting systems

2019 Fall National Meeting

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