Heat transfer during thermal processing of a temperature dependent non-Newtonian fluid in a tubular heat exchanger

Heat transfer is highly dependent upon fluid properties and operating conditions for a particular heat exchanger. Determination of heat transfer coefficients in aseptic processing of a temperature dependent non-Newtonian fluid (banana puree) as a function of steam temperature, flow rate and heat exchanger's length/diameter ratio is essential for modeling the thermal process. A commercial acidified aseptic banana puree with an average pH of 4.49 and average soluble solids concentration of 22.1 degrees Brix was processed in a tubular heat exchanger with two heating sections. Three flow rates (2.5 x 10(-5), 3.7 x 10(-5) and 4.7 x 10(-5) m(3) s(-1)), three steam temperatures (110.0, 12 1.1 and 132.2 degrees C) and two length (L)/diameter (D) ratios (250 and 500) were studied. Density, thermal conductivity and specific heat capacity were considered constant and heat transfer coefficients were calculated from the temperature data obtained. For an L/D ratio of 500, heat transfer coefficients varied from 654.8 to 842.2 W m(-2) K-1, while for an L/D ratio of 250 heat transfer coefficients varied from 735.5 to 1070.4 W m(-2) K-1. An empirical correlation was proposed and verified, which explained the experimental data within 10% error. (c) 2006 Elsevier B.V. All rights reserved.