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Heat transfer rates were measured for steam-heated, rotating cans containing potato spheres in water. Can rotational speed (9.3-101 rpm), sphere size (22.2-35.0 mm), and potato volume fraction (0.107-0.506) were varied in 14 triplicated experiments. Overall heat transfer coefficients were correlated within 225% with physical properties and operating variables by an equation derived by dimensional analysis. Film coefficients (h,) for heat transfer from the water to potatoes in the can were determmed by thermocouple measurement of potato surface temperatures; values were found to be finite and nearly invariant, averaging h, = 160 * 30 W/m*K. The lack of variation of hp suggested that for the experimental conditions tested, there was little relative motion between liquid and particles.

A mathematical procedure was developed to estimate heat transfer coefficients for heated rotating cans of food comprised of a liquid and spherical particles. The method uses experimental data for only the fluid temperature, and heat transfer coefficients are obtained by comparing predicted with experimental fluid temperature data in the Laplace transform plane. Results obtained using the procedure were compared with experimentally obtained heat transfer coefficients from the literature for three cases: potato spheres in deionized water, Teflon spheres in deionized water, and aluminum spheres in silicone fluid. Agreement between predicted and experimental results depended upon the agreement of the experimental conditions and the assumptions associated with the model.

High temperature thermal death parameters for Bacillus sfearofhermophilus TH24 (NCDO 1096) spores in water were determined using a computer-controlled reactor. The equipment produced and recorded accurate, reproducible square-wave temperature transients during very short heating times (-0.1 set). Survivor curves and the phantom thermal death time (TDT) curve between 130°C and 155°C from reactor data were compared to results from oilbath-heated capillary tubes between 115°C and 135°C. The TDT curve was nonlinear in the high temperature range but could be described by two lines with z = 9.3C for temperatures between 115°C and 145°C and z = 16.9C" for temperatures above 145°C. An Arrhenius plot did not represent the data better.

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