Estimation of Filtration Efficiency – from Simple Correlations to Digital Fluid Dynamics

AbstractAerosol filtration in fibrous filters is one of the principal methods of accurate removal of particulate matter from a stream of gas. The classical theory of depth filtration of aerosol particles in fibrous structures is based on the assumption of existing single fibre efficiency, which may be used to recalculate the overall efficiency of entire filter. Using “classical theory” of filtration one may introduce some errors, leading finally to a discrepancy between theory and experiment. There are several reasons for inappropriate estimation of the single fibre efficiency: i) neglecting of shortrange interactions, ii) separation of inertial and Brownian effects, ii) perfect adhesion of particles to the fibre, iv) assumption of perfect mixing of aerosol particles in the gas stream, v) assumption of negligible effect of the presence of neighbouring fibres and vi) assumption of perpendicular orientation of homogenous fibres in the filtration structure. Generally speaking, “classical theory” of filtration was used for characterization of the steady - state filtration process (filtration in a clean filter, at the beginning of the process) without deeper investigation of the influence of the nternal structure of the filter on its performance. The aim of this review is to outline and discuss the progress of deep-bed filtration modelling from the use of simple empirical correlations to advanced techniques of Computational Fluid Dynamics and Digital Fluid Dynamics.

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Influence of the aerosol flow and exposure time on the structural changes in the filtering half masks material

Journal of the Serbian Chemical Society ◽

10.2298/jsc170624004i ◽

2018 ◽

Vol 83 (4) ◽

pp. 463-471 ◽

Cited By ~ 1

Author(s):

Negovan Ivankovic ◽

Dusan Rajic ◽

Radovan Karkalic ◽

Dusan Jankovic ◽

Zeljko Radovanovic ◽

...

Keyword(s):

Structural Changes ◽

Aerosol Particles ◽

Direct Consequence ◽

Filtration Process ◽

Flow Rates ◽

Process Duration ◽

Aerosol Flow ◽

Flow Change ◽

Aerosol Filtration ◽

Theory Of Filtration

The flow of air and aerosol particles through the filtering half masks material depends on the structure porosity. It is very difficult to determine the behaviour of the filtering material during the process of extraction and retention of aerosols. The samples of five filtering half mask models were used in this investigation. Dynamics of the aerosol filtration through the filtering materials was tested using a method for testing the leakage of aerosol particles through the filtering material and a method for testing the inhalation resistance of filtering material, both specified in the SRPS EN 149:2013. Recording of the structural changes in the samples of the tested materials was carried out by the technique of scanning electron microscopy. The experiments showed a deviation of the results in relation to the theory of filtration the finely dispersed submicron sized particles. It was concluded that the aerosol leakage through the filtering half masks and their resistance to aerosol flow change depend on the aerosol flow rates and the on filtration process duration, as a direct consequence of the newly-made changes in the structure of the filtering material and due to reversibility effect between the filtration process and the changes in the filtering material.

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Filtration Model of Aerosol Particles by Fibrous Filters

Textile Engineering ◽

10.1115/imece2004-60873 ◽

2004 ◽

Author(s):

Wen Zhong ◽

Ning Pan

Keyword(s):

Aerosol Particles ◽

Filtration Process ◽

Fiber Cells ◽

Fibrous Filters ◽

Aerosol Filtration ◽

Numerous Cell ◽

System Energy ◽

Simulation Results ◽

The Difference ◽

Filtration Model

Aerosol filtration by fibrous filters is one of the most common methods of separating and removing particles in micro and sub-micro size ranges. The statistical genesis of this process can be regarded as the interactions and the resulting equilibrium among particle and fiber cells that comprise the system. Therefore a statistical mechanics approach, the Ising’s model, combined with Monte Carlo simulation, is employed in studying the process of the aerosol filtration through fibrous filters. The process is modeled as consisting of numerous cell state exchanges driven by the difference of system energy after and before a particle moves from one cell to the other and/or deposits on a fiber cell. With the use of a simpler binary algorithm, this approach is capable of realistically simulating the complicated mechanisms involved in the filtration process. For verification, simulations are carried out for the behaviors of aerosol particles of different sizes through isotropic fiber filters with various volume fractions. Simulation results are in good agreements with reported experimental data.

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