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Adsorption-Based Atmospheric Water Harvesting: Impact of Material and Component Properties on System-Level Performance
journal contribution
posted on 2019-05-15, 15:08 authored by Alina LaPotin, Hyunho Kim, Sameer R. Rao, Evelyn N. WangConspectusAtmospheric
water harvesting (AWH) is the capture and collection
of water that is present in the air either as vapor or small water
droplets. AWH has been recognized as a method for decentralized water
production, especially in areas where liquid water is physically scarce,
or the infrastructure required to bring water from other locations
is unreliable or infeasible. The main methods of AWH are fog harvesting,
dewing, and utilizing sorbent materials to collect vapor from the
air. In this paper, we first distinguish between the geographic/climatic
operating regimes of fog harvesting, dewing, and sorbent-based approaches
based on temperature and relative humidity (RH). Because utilizing
sorbents has the potential to be more widely applicable to areas which
are also facing water scarcity, we focus our discussion on this approach.
We discuss sorbent materials which have been developed for AWH and
the material properties which affect system-level performance. Much
of the recent materials development has focused on a single material
metric, equilibrium vapor uptake in the material (kg of water uptake
per kg of dry adsorbent), as found from the adsorption isotherm. This
equilibrium property alone, however, is not 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. We focus our discussion on modeling
a solar thermal-driven system. Performance of a solar-driven AWH system
can be characterized by different metrics, including L of water per
m2 device per day or L of water per kg adsorbent per day.
The former metric is especially important for systems driven by low-grade
heat sources because the low power density of these sources makes
this technology land area intensive. In either case, it is important
to include rates in the performance metric to capture the effects
of heat and mass transport in the system. We discuss our previously
developed modeling framework which can predict the performance of
a sorbent material packed into a porous matrix. This model connects
mass transport across length scales, considering diffusion both inside
a single crystal as well as macroscale geometric parameters, such
as the thickness of a composite adsorbent layer. For a simple solar
thermal-driven adsorption-based AWH system, we show how this model
can be used to optimize the system. Finally, we discuss strategies
which have been used to improve heat and mass transport in the design
of adsorption systems and the potential for adsorption-based AWH systems
for decentralized water supplies.
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m 2 deviceRHsorbent materialstechnology land areamass transportmaterial propertiesAdsorption-Based Atmospheric Water Harvestingadsorption-based AWH systemsequilibrium vapor uptakefog harvestingsolar-driven AWH systemperformanceSystem-Level Performance ConspectusAtmospheric water harvestingthermal-driven adsorption-based AWH system
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