Fittings losses in paste flow design

Abstract

Accounting accurately for the losses that arise from pipe fittings, such as valves, becomes a significant and important issue, given the current emphasis on energy reducing technologies. Efficient design is only possible if reliable loss coefficient data are available. For paste slurries which are in use in many industrial settings, this situation is exacerbated by the necessity to use less water, resulting in laminar flow designs becoming more common. Against this is the prevalent design reality that whilst reliable loss coefficient data are available for turbulent Newtonian flow, this is simply not the case for laminar flow. The objective of this paper is to show that fittings losses become much more prominent in laminar flow design. Work done by the authors for the measurement of loss coefficient data on diaphragm valves is reviewed and updated. This work, which is particularly important for paste flow applications, is then used to illustrate the importance of laminar flow loss coefficient data in the context of a practical design example. Pumping power requirement inaccuracies of the order of 50% are illustrated. The literature available to the paste piping designer contains a direct contradiction, and further research on this important practical issue is called for.