DETERMINING CONVECTIVE HEAT TRANSFER COEFFICIENT (h) FOR HEATING AND COOLING OF BOTTLES IN WATER IMMERSION (pages 54–75)

摘要

Thermal process, specially the in-package process, is one of the safestnand most frequently used methods for food preservation. Mathematical modelsnfor heat transfer have been widely used as a powerful tool in safety andnhigh-quality food process design. The convective heat transfer coefficient (h)nis essential for heat flux calculation in model boundary conditions, and itsndetermination must be done by the actual heat transfer system. The presentnstudy has determined the h-values for two commercial bottles (G1 and G2) inntwo water immersion systems, one for heating and one for cooling. It wasncalculated by an inverse heat transfer problem, using computational fluidndynamics. Two methodologies for h determination were compared, usingneither a conductive material or a convective material inside the packages. Thenmethodology that uses a conductive material showed simpler and faster computationalnsimulation, but presented a limitation related with the Biot numbernof the process. Results indicated a limitation in the most used methodology fornh determination, and suggest that the convective material methodology can benan alternative for this analysis. For the same systems, the hheating value for G1nwas almost 50% higher than for G2, and hcooling values for G1 were almost 70%nhigher than for G2. Differences obtained between bottles highlight the need tondetermine h for the exact heat transfer system. Moreover, these results indicatenthat there is a potential for process optimization only by varying its packagenformat, as it can influence the heat flux for the packaging.