Improved heating-element configurations for a tunnel oven

Natural convection within a 1700 mm horizontally long, 350 mmx 350 mm squar e cross-sectioned oven, containing a symmetrically-positioned square-sectio ned inner body, has been measured. Attention was focused on the effects tha t three hearer configurations have on the steady-state rate of heat transfe r to the rectangular-sided, 175 mmx 175 mm square cross-sectioned inner bod y. The radiative fluxes to each of the inner-body's surfaces have been calc ulated for the different configurations, using a multi-zone radiation model . Evacuating the enclosure permitted the convective component of the steady -state heat transfer to be identified. Thence, an easily applicable empiric al correlation, of the form (Q) over dot(conv) = n(1)(log(e) (Q) over dot(i n)) + n(2) was deduced for the natural-convection contribution. Overall, th e proximity of the heating element to the inner body dictated the proportio ns of the rates of heat that are transferred by radiation and convection. F or enhanced convective-heating, configurations with the heaters mounted alo ng the lower section of the sidewall, are recommended. (C) 1998 Published b y Elsevier Science Ltd. All rights reserved.