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|dc.description.abstract||The encapsulation of devices sensitive to moisture is necessary to prolong lifetimes under adverse environmental conditions. Therefore, quantifying moisture flow is important in design and verification of the encapsulations. Gaseous flows have been studied after Knudsen’s paper appeared in 1909, with one important exception: water vapour. A recent unexpected finding from Holt et al. concerned ultra-fast water and air flows in carbon nanotubes. While Gruener and Huber did not obtain ultra-fast nitrogen flows in silicon nanotubes. This leaves us to concern main effective factors for flows in tubes.
We use a theory of extended Navier-Stokes equations, having one equation for all flow regimes with an empirical parameter (Cha and McCoy theory), for predicting flow rates of nitrogen and water vapour through a 25 μm diameter silica glass cylindrical tube under isothermal condition.
We measure nitrogen flow rates through microtubes across a wide range of Knudsen number (0.0048 ~ 12.4583) using a two-chamber method. We find that the nitrogen flow obeys the Cha and McCoy theory with values of the tangential momentum accommodation coefficient (TMAC) α= 0.91 at small Kn and α close to one at large Kn, consistent with the redefinition of α by Arya et al.
We obtain fast transport of water vapour compared to the predictions from the Cha and McCoy theory over a range of pressures using the two-chamber method and a mass loss method. We attribute the excess flows to: (1) a thin adsorbed layer of chain-like water on the walls reducing the TMAC at low pressures; (2) liquid or two-phase flow appearing for inlet pressure close to saturation pressure. A theory for TMAC is developed based on the Langmuir adsorption.
We measure interdiffusive flow rates of water vapour in atmospheric air for the first time using the mass loss method and compare experimental results with ideal gas interdiffusive flow theory. We find interdiffusive flows of water vapour in air agree with the theory except for the case where water vapour partial pressures are close to the saturation pressure. Liquid or two-phase flow causes an enhancement of the interdiffusive flow by up to three orders of magnitude.
Using the available theories we predict the dominant flow types as a function of channel diameter and make recommendations on the moisture hermeticity testing in devices.||en_AU|
|dc.publisher||University of Sydney||en_AU|
|dc.publisher||Faculty of Science||en_AU|
|dc.publisher||School of Physics||en_AU|
|dc.subject||Water vapour flow||en_AU|
|dc.title||The physics of water leaks and water nanoflows||-|
|dc.type.pubtype||Doctor of Philosophy Ph.D.||en_AU|
|Appears in Collections:||Sydney Digital Theses (Open Access)|
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