Velocity and temperature profiles, heat transfer coefficients and residence time distribution of a temperature dependent Herschel-Bulkley fluid in a tubular heat exchanger

Banana puree was studied as a temperature dependent Herschel-Bulkley fluid. Experiments were conducted in a tubular heat exchanger at three flow rates (2.5 x 10(-5), 3.7 x 10(-5) and 4.7 x 10(-5) m(3) s(-1)), at three steam temperatures (110.0, 121.1 and 132.2 degrees C) and two length/diameter ratios (250 and 500). The minimum, maximum and average residence times were calculated from on-line electrical conductivity measurements. Inlet and outlet temperatures were recorded. A model was proposed to obtain heat transfer coefficients and velocity and temperature profiles in the heat exchanger. The continuity, energy and momentum equations were integrated using a finite difference method. The heat transfer coefficients varied from 654.8 to 1070.4 W m(-2) K-1 for average velocities of 0.24-0.40 m s(-1). There is good agreement between experimental parameters and those predicted by the model. (c) 2005 Elsevier Ltd. All rights reserved.