MEASUREMENT AND MODELLING OF STRUCTURE AND PORE LEVEL PROCESSES IN FILTERS AND WICKS

Abstract

Characterisation of new filtration and wicking materials through a 'wet-bench" testing process is a requirement for many filtration companies before new products can be released to market. A reduction in this testing commitment through the application of successful computational based models, requiring minimal empirical input, would undoubtedly result in huge financial savings and reductions in testing lead times. Such models could offer total media characterisation and could also aid further insights into many filtration and wicking processes which before would have required an expensive combination of different testing procedures. In this research, a depth filtration model has been developed, based on the three-dimensional void network model Pore-Cor, The geometry of the void network is fitted, by means of an 8-dimensional Boltzmann annealed amoeboid simplex, to the porosity and percolation characteristics of stainless steel sintered filters measured by mercury intrusion porosimetry (MIP). Preferential and critical flow paths through the network are calculated via a newly developed algorithm which allows a representation of net flow within individual pore/throat clusters. Particles from an experimental size distribution are fed along these flow-biased paths, using a newly developed random-particle-selection algorithm and, when straining occurs, the flow paths are re-calculated. The model is shown usefully to reproduce experimental filtration efficiencies as a function of pressure drop, measured by single pass tests. A critique of filtration efficiency measurements is given, suggesting use of a new 'alpha efficiency' rather than standard beta efficiency. The model is currently being adapted to accept porometry as well as porosimetry data, hence avoiding the use of mercury in future testing. Further to development of the filtration model the research associated with this thesis has also investigated two related areas. One is an investigation of a hydrophilic treatment of a series of polymeric sinters using oxidizing plasma. The investigation shows an improved method of data analysis of capillary rise measurements. An optimization process for determining the correct hydrophilic treatment parameters is proposed based on the variance across sample sets, and results are interpreted with respect to the Vyon® samples analysed. Secondly an investigation of anomalous compression characteristics found in the MIP of stainless steel Sinterflo® media is presented. Hypotheses were proposed for the observed increase in media compressibility and these were investigated using the Pore-Cor void network model for comparison with other investigations of porosity and compression analysis. Preliminary results suggest increased compressibility arises from microscopic material deformities and micro-fractures found in the media.