Modeling and experimental studies on aseptic processing of particulate foods

Jun Ho Lee, Purdue University

Abstract

A finite difference scheme was used to simulate an aseptic processing of particulate foods. Size, shape, thermal properties, and residence time distributions (RTDs) of particles within scraped surface heat exchanger (SSHE) and holding tube greatly influenced the accumulated lethality and minimum required processing time. Effects of the overall heat transfer coefficient for heater and holding tube and the particle surface heat transfer coefficient were significant. A sensitivity analysis indicated that particle size, density, and specific heat were the most sensitive parameters which influence holding tube length required while fluid thermal conductivity and viscosity were less susceptible to affect the model prediction. Product flow rate and initial temperature were also critical parameters. Minimum and maximum normalized particle residence times (NPRTs) and standard deviations of mean values were not significantly affected by the particle concentration for horizontal and vertical SSHEs. Mean NPRTs of up to 10% particle concentration were significantly lower than those of 20-40% for horizontal SSHE while those of 40% was significantly higher than those of single particle--20% for vertical SSHE. Mean NPRTs were also significantly influenced by viscosity of carrier, mutator speed, and particle size. Most of the individual particle RTDs in a vertical SSHE flow could be described by gamma model, whereas many of individual distributions fitted to normal model in addition to the gamma model for horizontal SSHE. Orientation of SSHE was an important factor to influence the forces acting on the particles. Liquid mean residence times (LMRTs) were not significantly influenced by particle concentration 0 to 30% in a holding tube. Variance was significantly higher without particle loading, resulted in broader distributions. Twenty percent particle loading significantly reduced the LMRTs in a horizontal SSHE. An increase in mutator speed significantly increased the variance, resulted in broader distributions. Effect of mutator speed was more dominant than the particle concentration to influence liquid RTDs in the SSHE. The LMRTs calculated from volumetric flow rate were lower than those from the pulse input experiments for holding tube and SSHE. Thermal process calculations based on the former may result in considerable overprocessing of liquid portion of the product.

Degree

Ph.D.

Advisors

Singh, Purdue University.

Subject Area

Food science|Agricultural engineering|Mechanical engineering

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