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UBC Theses and Dissertations

A study of heat transfer from steam-air mixtures to a retort pouch substrate Kisaalita, William Ssempa


Thermal processing of foods in retort pouches using steam-air mixtures may offer advantages over alternate techniques; however, thermal properties of steam-air mixtures are not well understood. Since retort pouches are becoming increasingly common, it is important to know the heat transfer characteristics of steam-air mixtures in order to permit their efficient utilisation. In this study, a sensor was designed for measuring the heat transfer coefficient of steam-air mixtures using a retort pouch laminate as the condensation surface. This was incorporated into a condensation chamber that was designed to accommodate steam-air mixtures, up to 50% steam at a maximum temperature of 125°C. With steam-air media flowing horizontally and on the underside of a retort pouch substrate, the nature of condensation was investigated, as well as the effects of temperature, Reynolds number and the diffusion coefficient on the heat transfer coefficient. It was concluded that the release of enthalpy from steam-air mixtures on the underside of a retort pouch substrate was by filmwise condensation. It was also concluded that the heat transfer coefficient could be predicted by exponential functions of the surface temperature, and the temperature difference between the steam-air medium and the substrate surface. The dependence of the heat transfer coefficient on the diffusion coefficient was found to be stronger at high temperature differences.

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