Design and development of a prototype radio frequency applicator for post baking biscuits

Abstract

Manufacturing biscuits in a factory involves several processes like mixing, moulding, baking, cooling and packaging. Out of these the baking process is a major quality deciding and energy consuming process. In the baking process, the moulded biscuit dough is passed into baking oven and the biscuits are heated to desired temperatures to remove the moisture. In the oven the heat transfer to the biscuits happen by the conventional methods of heating namely conduction, convection, radiation. When the biscuits are baked by the conventional heating methods a condition called checking arise which can result in cracking of biscuit at centre. Checking is caused due to the build-up of stresses in the biscuit due to the differential moisture content between the outer surface and the centre surface of the biscuit. The differential moisture content exists in conventional heating because the heat energy has to pass from the surface by conduction to the interior of the biscuit. Often this can present a problem, and as such it is difficult to get the heat to penetrate to the centre of the product. Therefore, the surface dries out, while the core or centre of the biscuit remains high in moisture. Radio Frequency (RF) post baking of biscuits can overcome the problem of checking in biscuits by selectively removing the differential moisture content by RF dielectric heating. In its simplified form the RF post baking system will consist of a RF high frequency source coupled to the applicator (oven) through an impedance matching network. The baked biscuits will be RF dielectric heated in the applicator for removing the differential moisture. The ability of the applicator to have better RF power uniformity/heating uniformity on the biscuit being heated is important for achieving efficient design. The RF power uniformity/heating uniformity is defined by a metric called power uniformity index. The objectives of this research were to investigate the influence of various factors of the applicator design like inter electrode gap, material o