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Pouring of Grains onto Liquid Surfaces: Dispersion or Lump Formation?

Ong, Xin Yi, Taylor, Spencer E. and Ramaioli, Marco (2019) Pouring of Grains onto Liquid Surfaces: Dispersion or Lump Formation? Langmuir, 35 (34). pp. 11150-11156.

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This study considers the consequences of adding grains to an air−liquid interface from a funnel. Depending on the grain contact angle and liquid surface tension, the interface is found to support a single or multiple layers of grains, forming a granular stack. By continuing to add grains, the stacks grow until either the lower grains disperse in the liquid, or the complete stack breaks free from the surface and sinks as a dry powder lump. Herein, the effects of grain contact angle, density, and size on these processes are studied experimentally, and a theoretical analysis is given. The maximum number of grains contained in a floating stack and its critical depth are observed to increase as the grain size decreases. The maximum number of grains scales with the bond number (Bo) as Bo−1.82 when stack detachment is observed and with an exponent −2.0 when grains disperse into the liquid. As a result of these different scaling exponents, a critical bond number above which grains wet and disperse can be identified. Favorable conditions for dispersion are achieved with larger grains and, to a lesser extent, by lower surface tension and contact angle. The critical bond number separating grain dispersion from lump formation increases with an increasing grain contact angle, thus providing a physical justification for increasing grain size with common processes such as granulation or agglomeration. Conversely, a quantitative framework to interpret the limitations in dispersing small grains is proposed, justifying the need for low contact angle or liquids with low surface tensions, both favored by the use of surfactants. The present findings have identified conditions under which lump formation occurs, and hence how these undesired phenomena can be avoided in applications requiring the efficient dispersion of grains across a liquid interface.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Chemical and Process Engineering
Authors :
Ong, Xin
Taylor, Spencer E.
Ramaioli, Marco
Date : 8 August 2019
DOI : 10.1021/acs.langmuir.9b01277
Copyright Disclaimer : This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Langmuir, copyright © 2019 American Chemical Society after peer review.
Depositing User : Diane Maxfield
Date Deposited : 10 Jan 2020 14:50
Last Modified : 13 Jan 2020 11:57

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