Improvement of Heat Transfer During Low Temperature Pasteurization Processes

摘要

Heat transfer control remains important during pasteurization of a foodstuff or ready-to-eat meal. This paper presents a new stirring system which can be used in a water cooking bath. This system, besides increasing the heat transfer rate, decreases the temperature gradient in the cooking bath. Air bubbles are introduced at the bottom of the bath and their ascent promotes stirring and uniformity of the bath temperature during cooking. Stirring efficiency has been estimated experimentally. The factors involved are: position of the foodstuff (horizontal or vertical), air mass flow rate and volume occupation ratio of the foodstuff in the cooking bath. The heating rate was estimated from the temperature rise at the centre of a slab of methylcellulose gel which was used as a model food. Analysis of the results indicates that bubbles significantly increase the heating rate of the heat transfer phenomenon. It also shows that the effect of bubble stirring is much more efficient when the slabs are in a horizontal than in a vertical position.