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 × 10−5, 3.7 × 10−5 and 4.7 × 10−5 m3 s−1), at three steam temperatures (110.0, 121.1 and 132.2 °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.