Validation of heat transfer and friction loss data for fibre suspensions in a circular and a coaxial pipe heat exchanger

Abstract

Heat transfer data obtained previously in a pipe heat exchanger were validated using an annular test unit with longer calming section and axial entry flow levels. Water and two suspensions of long-fibre softwood Kraft pulps with fibres having different coarseness (mass/unit fibre length) were used. Data in both systems were accumulated and compared over a range of flow rates with the fibre concentrations up to 0.4%. Heat transfer coefficient hc increased with increasing velocity for both water and fibre suspension flow. Various fibre dimensions and fibre characteristics are shown to vary systematically with hc at the same experimental conditions in both flow systems. The data from a pipe and an annular coaxial pipe heat exchanger for fibre suspensions of concentrations 0.2 and 0.4% show that the relationships among heat and momentum transfer and fibre characteristics and specific properties of paper can be obtained with confidence from either type of heat exchanger.