First set of simulations should be without chemistry (Wojciech email 12/06)

Benefits of different particle types:

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  solid ceria

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    more reducible material per particle

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    more dense, requires higher flow rate

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    more material means more absorption so more concentrated irradiation is used to drive chemistry

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  ordered, highly porous ceria

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    transport of oxygen into and out of solid ceria is easier

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    lower density so easier to keep in suspension… allows flexibility in choosing flow rate to adjust for changes in solar flux… also tradeoff with convective losses

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    geometry may lead to high absorption or radiative energy per volume of ceria

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    increased surface area leads to increased reaction release and uptake

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    A degree of radiative property tunability was shown to be attainable by varying the internal pore structure as well as the overall particle size. Larger pores were shown to lead to broadening and decay of the absorption efficiency factor peak, redshifting and decay of the scattering efficiency factor peak, and a trend away from isotropic scattering. Increases in particle size leads to similar effects \cite{Randrianalisoa_2014}. Since ceria naturally absorbs well only in the ultraviolet region, any redshifting of of absorption peaks should lead to significant improvements in solar-weighted absorption. A scattering peak near the peak of the solar spectrum is also desirable to reduce direct irradiation of the back of the reactor by redistributing radiation within the cloud allowing for more chance of absorption. In this paper, we highlight the dramatic effect such tunability can have on the macroscopic behavior of a cloud of such particles undergoing thermal reduction.

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  randomly porous ceria

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    marriage of the two benefits and drawbacks

Previous studies show that, not surprisingly, smaller particles provide a more constant temperature profile leading to a more uniform reaction within the media [cite grampp]. This is desirable since we want to every particle within the reactor to reach full reduction before exiting. However, this constant temperature profile was achieved largely due to the transparency of the particles, and therefore the particle slab, thus the percent of concentrated solar irradiation transmitted through the particle slab and impinging on the wall was very high leading to very high losses and impractical conditions for realistic reactor design.

Faster heating rates means we are able to cycle particles faster and therefore achieve more prolific production of oxygen.

But Roman’s paper says the reaction rate cannot keep up with the heat transfer rate! This means heating up the particle faster is not necessarily better because we will only get more losses with no gain. How do we balance that?

We are looking for uniform and complete absorption.