Removal of Yield-Stress Fluids from Pipework Using Water

The emptying of product from process plant is a significant multiphase flow problem in food and personal care industries, controlling both product recovery, and cleaning time. Product and operational losses can be significant, especially with viscous products. It is necessary to maximize product recovery while minimizing cleaning time and effluent volume. The removal of a range of products from fully filled pipework using water has been characterized and monitored by weighing pipes at intervals and by inline turbidity probe. Data is presented for a range of products (toothpaste, hand cream, apple sauce, yoghurt, and shower gel) that have been cleaned from two pipe systems. The data can be fitted by a linear relationship between a dimensionless cleaning time, and the ratio of the product yield stress to the surface shear stress. The effect of pipe fittings is to reduce cleaning times, reflecting increased shear/energy dissipation in the pipe. (C) 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers