Process evaluation for aseptic processing of particulate foods in tubular heat exchangers: Simulation and experimental verification
Abstract
A finite difference simulation of heat transfer to Power-law fluids, in a tubular heat exchanger, with temperature dependent viscosity and density was carried out to evaluate a thermal process by varying experimental parameters. The DuFort-Frankel finite difference technique was applied in solving the coupled continuity, momentum and energy balance partial difference equations. Thermal time distributions (TTD) were calculated to evaluate processing of non-Newtonian fluids in a tubular heat exchanger. The Eulerian approach was used to follow particles along their flow path and calculate thermal treatments received by individual particles. Reducing the tube diameter and lowering wall temperature achieved a lower spread in TTD indicating better quality food products. Fluid to particle convective heat transfer coefficient $(h\sb{f\sb{p}})$ was calculated from experimental measurement of particle temperatures along their flow path in a hold tube. The $h\sb{f\sb{p}}$ values ranged from 108-195 $W/m\sp2\sp\circ C$ for the temperature range of 22.22-82.22$\sp\circ C$ and Carboxy methyl cellulose concentration of 0.5-1.2% (w/w). Fluid viscosity significantly affected the $h\sb{f\sb{p}}$ values. A finite element simulation of particle heating in a non-Newtonian fluid in a tubular heat exchanger was successfully implemented. Temperature distribution on the surface of the particle along its flow path was considered. Destruction of peroxidase and C. sporogenes (PA3679) were studied. Factors studied included the $h\sb{f\sb{p}}$, initial fluid and particle temperatures, particle size, and flow properties. Results showed that temperature distribution on the particle surface, $h\sb{f\sb{p}}$ and particle size played an important role in particle sterilization. Fluid properties did not have a major effect on the particle sterility. Experimental verification of the simulation was carried out using calcium alginate spheres with Horseradish peroxidase as a chemical indicator of thermal treatment. D and Z values were obtained in TDT cans for a temperature range of 100-130$\sp\circ C.$ A procedure to make spherical particles of dehydrated potato (BUD) in alginate loaded with Horseradish peroxidase was developed and used as an indicator of thermal treatments. Particles were processed in a continuous flow pilot scale system at temperatures of 110, 120 or 130$\sp\circ C.$ Destruction of peroxidase was related to the amount of thermal treatment received and were used to verify the numerical simulation.
Degree
Ph.D.
Advisors
Singh, Purdue University.
Subject Area
Food science
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