This paper presents a model for the initial particle deposition in a deepbed filter with a sphere‐in‐cell porous media model used. The analysis includes all the relevant mechanisms, and the results indicate that deposition occurs under favorable surface interactions. A semiempirical expression relating collection efficiency and operating parameters is presented.
Two porous media models — capillaric and Brinkman — were used for the study of deep bed filtration and to calculate the filter coefficient and the pressure drop increase during the course of filtration.
The filter coefficient was estimated with trajectory calculations which determine the path of particulate matters as they pass through the filter. A number of relevant forces were included and their effects determined. The Brinkman model was found to give good agreement with experimental results and the filter coefficients based on capillaric model were approximately one to two orders of magnitude lower than experimental data.
Both models fail to give reasonable estimates on the pressure drop increase and the discrepancies between the model and the experimental values were two to three orders of magnitude. This is largely due to the failure of the models to distinguish the different roles played by the filter grains and by the particulate matters retained. The filter grains constitute a matrix of passages as conduits for the liquid flow, and the deposited particulate matters act primarily to modify these flow passages (i.e. to restrict the flow). Such a distinction is however not possible with the use of these models.
The use of tracer dispersion measurements in conjunction with associated pressure drop data, as an indirect diagnostic technique for the determination of particle deposit morphology in deep‐bed filters, was investigated. The dispersion measurements consisted of the injection of an electrolyte tracer pulse at the inlet and the monitoring of the tracer peak as it traveled down the bed, while the pressure drop data consisted of the axial pressure gradient histories as deposition took place. These data are interpreted using dispersion and pressure drop theories established on the basis of assumed models of deposit morphology. The validity of this technique was confirmed experimentally.
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