LWT 40 (2007) 1240–1245 System variables affecting heat transfer in a canned particle in Newtonian fluid system during end-over-end rotation Yang Meng, Hosahalli S. Ramaswamy à Department of Food Science, McGill University, Macdonald Campus, 21,111 Lakeshore Ste-Anne-de-Bellevue, PQ, Canada H9X 3V9 Received 25 January 2006; received in revised form 26 July 2006; accepted 17 August 2006 Abstract Heat transfer in a canned particle/Newtonian liquid system was evaluated in a pilot-scale, full water-immersion single-cage rotary retort. High-viscosity aqueous glycerin solutions (from 75% to 100%, V/V) were used as Newtonian liquids and the effects of rotation speed, glycerin concentration, retort temperature, can size and particle material on heat-transfer rates to products were investigated. A full factorial experiment design and a CCRD experiment design were used. Flexible thin wire thermocouples and rigid thermocouples were used to measure particle temperatures and liquid temperatures, respectively. Apparent heat-transfer coefficients h ap and apparent overall heat-transfer coefficients U a were evaluated during end-over-end rotation. The h ap values increased with increase in rotation speed, retort temperature and particle density, and a decrease in liquid viscosity and can size. U a values increased with an increase in rotation speed and a decrease in liquid viscosity. r 2006 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. Keywords: Heat-transfer coefficient; Viscosity; Newtonian fluid; Particulate liquid; Retort; Thermal processing; Agitation 1. Introduction For establishing and optimizing thermal processing, an appropriate methodology to predict and deliver a process lethality (F o ) is essential. Although heat penetration parameters are commonly used for this purpose, in combination with process calculation methods like Ball and Stumbo, the computerized approach suggested by Teixeira, Dixon, Zahradnik, and Zinsmeister (1969) is increasingly getting popular both for process control and optimization. This approach is based on numerical solution to heat transfer and makes use of data on thermophysical properties and associated heat-transfer coefficients with the system. For particulate liquid canned foods, such as sauces containing vegetables or meat chunks, the overall heat- transfer coefficient U, which is the heat-transfer coefficient between heating medium and liquid, combined with fluid- to-particle heat-transfer coefficient h fp , which is the heat- transfer coefficient between liquid and particle surface, can be used to predict the particle and liquid temperature profiles and then the process lethality. Heat-transfer coefficients can be much more easily coupled with heat-transfer models than the conventional heat penetration parameters when using computerized approaches. Several studies have been conducted on the effects of system variables on h fp and U values (Lekwauwa & Hayakawa, 1986; Lenz & Lund, 1978; Deniston, Hassan, & Merson, 1987; Fernandez, Rao, Rajavsireddi, & Sastry, 1988; Stoforos & Merson, 1992; Sablani & Ramaswamy, 1995, 1996, 1997, 1998, 1999). Results have shown that, for canned particulate liquid foods in rotary retorts, variables affecting the heat transfer to products include rotation speed, retort temperature, head space of the can, rotation radius, particle size, can size, particle material, particle concentration and liquid viscosity. Most of the previous studies (Lenz & Lund, 1978; Lekwauwa & Hayakawa, 1986; Deniston et al., 1987; Fernandez et al., 1988) used restricted particles in the can, which cannot simulate the particle motion during agitation processing. Stoforos & Merson (1992), Weng, Hendrickx, ARTICLE IN PRESS www.elsevier.com/locate/lwt 0023-6438/$30.00 r 2006 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2006.08.010 à Corresponding author. Tel.: +1 514 398 7919; fax: +1 514 398 7977. E-mail address: Hosahalli.Ramaswamy@McGill.ca (H.S. Ramaswamy).