Offset screen and pseudodiffusion models for prediction of filtration phenomena in real fibrous filt...

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" Offset screen and pseudodiffusion models for prediction of filtration phenomena in real fibrous filter media "
A. M. Khan M. Faghi

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112498
Doc. No	:	TLpq303856771
Main Entry	:	A. M. Khan
	:	M. Faghi
Title & Author	:	Offset screen and pseudodiffusion models for prediction of filtration phenomena in real fibrous filter media\ A. M. KhanM. Faghi
College	:	University of Rhode Island
Date	:	1990
student score	:	1990
Degree	:	Ph.D.
Page No	:	298
Abstract	:	The existing filter models do not account for the microscale inhomogeneities and the three-dimensional random fiber dispersion present in real media. Such models either fail to assume a realistic geometrical description of the actual fibrous matrix or idealize the complex three-dimensional fluid flow. Consequently, none of the approaches to the modelling of fibrous filters are capable of adequately predicting the performance of real fibrous filter media. To overcome the shortcomings, a three-dimensional microstructural Offset Screen Model has been developed to simulate filtration phenomena in fibrous filters. The model is based on the hypothesis that a realistic fibrous filter model must account for the structural properties of the media, namely, the fiber size, solidity and anisotropy. In addition, the microscale random pore size distribution must be represented in the filter model. A typical module constructed according to the offset screen theory is constituted of arbitrarily offset screens in the streamwise direction. Using finite volume discretization the full Navier-Stokes equations have been solved under periodicity conditions along all the three space coordinates. Pressure drop predictions have been obtained for the whole range of filter solidities for isotropic and anisotropic media for Reynolds numbers up to 30. The predictions from the offset screen model are in excellent agreement with the data obtained from the real fibrous filter media. The anisotropy in filter media results in higher pressure drops for solidities larger than 0.2. The pressure drop for inertia driven flows increases nonlinearly with the flow rates. The Offset Screen Model calculates particle capture efficiencies in real fibrous filter media due to Brownian diffusion, inertia, and interception. Collection of point inertialess particles due to Brownian diffusion has been calculated by solving the particle conservation equation with the assumption of periodic fully developed concentration profile in streamwise as well as the other two coordinates. The predictions from the offset screen model have been compared with the experimentally measured overall filter efficiencies of real fibrous filter media over the range of parameters 22 usd< Pe\leusd 1.902 usd\timesusd 10, 3.80 usd\timesusd 10 2.575, 0.0091 usd\le I\leusd 0.1182, 0.00733 usd\le Re\leusd 2.68 for low to high filter solidities. The predictions from the offset screen model have been found to be in reasonably good agreement with the experimental data for diffusion dominated or inertia dominated regimes. (Abstract shortened with permission of author.)
Subject	:	Applied sciences
	:	fibrous filter media
	:	Mechanical engineering