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Heat transfer in canned particulate system in Newtonian and non-Newtonian liquids was studied during end-over-end agitation thermal processing in a pilot scale rotary retort. Computational methods for conventional overall heat transfer coefficient (U) and fluid to particle heat transfer coefficient (hfp) were found unsuitable in high viscosity fluids. A methodology for evaluating an apparent heat transfer coefficient (hap) between retort medium and particle, and an apparent overall heat transfer coefficient Ua between retort medium and can fluid was proposed. Use of h ap and Ua concepts permitted direct predictions of particle temperature and lethality based on retort temperature. / An L-16 orthogonal experimental design of experiments was carried out to select system factors that significantly affected hap and U a values for particles in high viscosity non-Newtonian and Newtonian fluids. Experiments using central composite rotatable design and full factorial design were carried out to study the effects of selected significant factors on hap and Ua. / Using all data obtained, dimensionless correlations were developed for the prediction of hap and Ua values. The developed correlations showed a good agreement with the experimental data. More precise predictions were achieved with trained artificial neural network (ANN) models. The results of ANN models could be compiled using algebraic equations and were included so that hap and Ua values could be predicted without actually using the ANN software. A flow visualization study was conducted to better understand the heat transfer behavior in high viscosity fluids. Results showed that in particulate high viscosity fluids, the particle liquid relative movement was very weak, implying that the heat transfer between them could converge to conduction-conduction rather than convection-conduction, which results in erroneous and unusually large hfp values.

Heat transfer to canned particulate laden Newtonian fluids was studied during free axial agitation thermal processing in a pilot STOCK retort which was modified to simulate the can motion in continuous turbo cookers. Evaluation of heat transfer coefficients (overall, U and fluid to particle, hfp) associated with canned liquid/particle mixtures, while they are subjected to free axial motion is difficult because of the problems involved with attaching temperature measuring devices to liquid and particles without affecting their normal motion. A new methodology was developed to evaluate U and hfp in Newtonian liquids. The methodology involved first correlating U and hfp as a function of input variables for cans in fixed axial mode of rotation in which both particle and fluid temperatures were measured using thin wire thermocouples. Subsequently, only liquid temperatures were measured in cans using wireless sensors in the free axial mode, and hfp values were empirically computed from the developed correlations and the measured temperatures. An L-16 orthogonal experimental design of experiment was carried out to select system and product parameters that significantly influence hfp and U for particles in the Newtonian liquid. With significant parameters selected, a response surface methodology and two full factorial experimental designs were used to relate U and hfp to process variables in each mode of rotation (fixed and free axial modes). / Dimensionless correlations were then developed using the evaluated data for heat transfer coefficients (U and hfp), in canned high viscosity Newtonian liquids (with and without particles) using stepwise multiple non-linear-regressions of significant dimensionless groups. In free axial mode, combining the natural and forced convection, Nu = A 1(GrxPr)A2+ A3(Re) A4 (Pr)A5 FrA 6 (rhop/rhop1)A 7 (e/100-e)A8 (dp/Dc) A9 (Kp/K1)A10 yielded a higher R2 (0.93) than using a pure forced convection model when particles were present in the can. Even in the absence of particles, and with the end-over-end mode of agitation where forced convection dominates, introducing natural convection term (GrxPr), improvedR2 from 0.81 to 0.97. Artificial neural network (ANN) models were also developed for heat transfer coefficient predictions and the trained models gave better predictions than dimensionless correlations. All ANN models developed could be implemented easily in a spreadsheet as either matrices or a set of equations.

Graduation date: 1991

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High pressure (HP) sterilization of low acid foods is a process involving HP at elevated temperatures. Data available on HP destruction kinetics of pressure resistant pathogenic, spoilage-causing and surrogate bacterial spores are limited, but essential for establishing such a process. While compression heating could be employed to provide the elevated temperature, accurate data gathering under such conditions is difficult due to rapid heat loss during the treatment. The objectives of this research were to first standardize the set up carrying out HP tests at elevated and stabilized temperatures, and subsequently to evaluate HP destruction kinetics of selected bacterial spores under HP elevated temperature processing conditions. / The set-up consisted of a thick insulated chamber for holding samples during the test. A relationship was established for the adiabatic temperature rise milk which was used as the main low acid food medium: DeltaTP = -0.306 + 0.0224Ti + 0.0423P + 4.49x10-4T i2 + 1.31x10-4TiP -- 1.24x10 -5P2 (R2 =0.999, n = 50, SE = 0.20°C, p<0.05). Initial temperatures at 83.5, 91.7, 95.8°C and 80.7, 88.9, 93.0°C provided operating process temperature 121, 130, 135°C, at 800, 900MPa, respectively. / Destruction kinetics tests were carried with two strains of Clostridium sporogenes (11437, 7955) and Geobacillus stearothermophilus 10149 spores suspended in milk at 700-900 MPa and 70-100°C. These strains were selected for their relatively high pressue and thermal resistance. The survival counts were well fitted by first order linear models. The D values C. sporogenes 11437 varied from 0.73 min at 900 MPa 100°C to 17.0 min at 700 MPa 80°C HP treatments while they ranged from 6.0 to 833 min at 80-100°C under thermal processing conditions. The D values associated with of C. sporogenes 7955 spores were higher and varied from 1.3 min at 900 MPa 100°C to 38.2 min at 700 MPa 80°C HP treatments, and from 12.1 to 156 min at 80-100°C during thermal treatments. The D values of Geobacillus stearothermophilus 10149 spores varied from 0.6 min at 900 MPa 90C to 20.9 min at 500 MPa 70°C HP treatments with 6.3 to 49.4 min for thermal treatments at 110-120°C. Hence C. sporogenes 7955 spores were the most resistant among those studied. The HP destruction kinetics of C. sporogenes 7955 spores were also studied in salmon and were lower than in milk. / Pressure resistance screening of selected group I C. botulinum spores was carried out at 800-900 MPa at 90-100°C. Nominal D values of each strain were evaluated which demonstrated that PA9508B, H09504A and CK2-A were the more resistant spores (PA9508B > HO9504A > CK2-A). HP destruction kinetics of C. botulinum PA9508B spores in milk were evaluated in detail at 700-900 MPa at 90-100°C and parallel thermal treatment at 90-100°C. The survival counts were again described by first order linear models (R2 >0.86). The D values varied from 0.35 min at 900 MPa 110°C to 38.9 min at 700 MPa 90°C for HP treatments and 14.4 to 273 min at 90-100°C for thermal treatments. These demonstrated that HP processing combined with elevated temperatures will accelerate the spore destruction rate. However, the associated D values of C. botulinum PA9508B spores in milk were more resistant than those of C. sporogenes 7955 at 90, 100°C, which indicated that the surrogate may not be very effective for using as a target for verification HP at elevated temperature processing conditions. / Overall, this work has demonstrated several findings. The non-pathogenic C. sporogenes 7955 spore was the most resistant surrogate but the pathogenic C. botulinum PA9508B spore was even more resistant. D values associated with HP at elevated temperatures were higher than under conventional thermal treatments, and hence provide accelerated destruction kinetics at least for the non-pathogenic spores and hence better spoilage control. However, from safety point of view the conventional thermal sterility requirements would still persist even under HP processing conditions. Milk as a low acid food medium provided more resistance for HP destruction than fish.

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