Thesis Details

Thesis Title: An investigation of the factors affecting the behavior of cotton textiles as filter fabrics
Thesis Author: Laconla Hance
Abstract: Utilizing Ruth's equations, the filtration resistance of cotton filter cloths is studied for systematic variations of cloth construction,factors and variations of many filtration factors in constant-pressure filtrations of an aqueous calcium carbonate slurry. The clarifying properties of the cloth are evaluated in terms of the time required to produce a clear filtrate, the amount of filtrate flowing in this time, and the amount of solids contained in the filtrate. The behavior of a fabric in a given filtration is expressed in measurable quantities which do vary for different fabric construction properties. For a wide variety of cotton filter cloths and filtration conditions, it is found that Ruth's proposals for linear, inverted-rate plots hold. The filtration resistance of the fabric includes not only the resistance to flow of filtrate but also the resistance resulting from the solids having throttled the fabric pores. Both of these resistances varied with the construction of the fabric. In general, the filtration resistance is found to be related to both the nature of the wet fiber surfaces in yarns and the fabric density. The following fabric properties are found to contribute to a low fabric resistance: 1) long floats and a small number of yarn interlacings per unit area of fabric, 2) low yarn twist, 3) loose texture, and 4) the presence of coarse, mature fibers rather than fine, immature ones. Initial use of the fabric, use of previously unwet fabrics, high filtration pressures, and fine particles of solids were also found to effect a low filtration resistance of the fabric. The amount of a given particle size of solids passed by a fabric appears to be related to the size and distribution of pores lying between the yarns of the fabric. Those factors which in general give low filtration resistances also effect an excessive passage of solids through the fabric except in the case of low yarn twist. In this case, a low resistance is obtained for 2/1 twill fabrics with little change in clarity of filtrate. The following fabric properties are found to contribute towards a small amount of solids being passed by the fabric: 1) short floats and a large number of yarn interlacings per unit area of fabric, and 2) close weave, Prewetting of fabrics, prolonged usage of a given piece of fabric, low filtration pressures, and coarse particles of solids also effect a low amount of solids being passed by the fabric. In general, twill fabrics are found to give lower fabric resistances but permit the passage of more solids than duck fabrics for similar fabric weights. Certain twill fabrics can be chosen, however, which offer low resistance and yet permit only a slight passage of solids. A mechanism for the theory of fabric behavior in filtration is presented in terms of the influence of fabric construction factors and filtration factors on flow through the fabric, resistance offered by the fabric, amount of solids passed, and the rate of clarification. It is concluded that fluid flow occurs through all portions of the fabric, i.e., through pores lying both between yarns and those lying within the yarns.