Particulate Science and Technology, 28: 51–66, 2010 Copyright © Taylor & Francis Group, LLC ISSN: 0272-6351 print/1548-0046 online DOI: 10.1080/02726350903405403 An Investigation into Modeling of Solids Friction for Dense-Phase Pneumatic Conveying of Powders S. S. MALLICK AND P. W. WYPYCH Centre for Bulk Solids and Particulate Technologies, Faculty of Engineering, University of Wollongong, Wollongong, Australia This article presents results from an investigation into the modeling of solids friction factor for fluidized dense-phase pneumatic conveying of powders. A fundamental design approach was pursued by employing “straight pipe” and “back calculation” techniques for modeling and using two types of power function formats. The “straight pipe” models were found to be unexpectedly different depending on the selected location of pressure-measuring tapping points (even for the same product). An attempt to explain this variation by studying the “straight pipe” conveying characteristics suggested significant changes in flow mechanisms along the pipe. The derived models were evaluated for scaleup accuracy and stability by predicting for larger and longer pipes. The results showed significant variations in predictions. One format of power function model was found to result in more stable predictions than the other. Possible explanations for the causes of such variations are provided. Physical observations of the flow phenomena of dense-phase conveying for different powders showed the products were mostly conveyed as a dense non-suspension liquid-type-layer along the bottom of the pipe. This mechanism does not seem to be correctly represented by the existing design approach of using a Froude number term in the solids friction factor models, thus initiating a search for suitable alternative dimensionless grouping(s) that can adequately represent the non-suspension flow phenomena. In this study, Steady-state conveying data of three different powders conveyed in various pipes (diameter/lengths) were used for the purpose of modeling and scaleup investigations. Keywords dense phase, pneumatic conveying, pressure drop, scaling up, solids friction Introduction The pressure drop for a straight horizontal section of pipe for a solids-gas mixture can be calculated using Equation (1), as given by Barth (1958). This expression was considered by Weber (1981) as being applicable only to coarse particles in dilute-phase flow. However, this equation has been used subsequently by various S. S. Mallick would like to thank the University of Wollongong for the International Tuition Fee Exemption Scholarship and the University Post Graduate Award (UPA), which have enabled him to undertake Ph.D. studies. Address correspondence to S. S. Mallick, Centre for Bulk Solids and Particulate Technologies, Faculty of Engineering, University of Wollongong, Wollongong, N.S.W. 2522, Australia. E-mail: soumyasuddha@gmail.com 51