A comprehensive experimental, analytical, and numerical investigation of the modes of heat transfer in an electrically heated oven.

摘要

A many-faceted, all-encompassing experimental, analytical, and numerical investigation has been performed to identify and quantify the heat transfer processes that occur in an oven containing a thermal load. Parametric variations were made of load characteristics such as surface finish, size, composition, and location; the radiation surface properties of the oven walls were also varied parametrically. In addition, the effect of a variety of supports for the thermal load, of the presence of blockages—both water filled and empty, and of different radiation properties of the supporting surfaces and blockages were quantified. Three other operating conditions were systematically investigated including: (a) surface finish of the temperature sensor which controls the on-off heating cycle of the oven, (b) various set-point temperature levels, and (c) open or closed state of the oven vents.; In the experimental phase of the work, time-varying temperatures were measured in the thermal load, in the air contained within the oven, on the various walls of the oven, and on the various blockages and load supports. Heat transfer rates at the thermal load were deduced from the aforementioned temperature measurements, and corresponding heat transfer coefficients were evaluated. These heat transfer coefficients were found to be quasi-steady. The experimentally determined heat transfer results were subsequently used to examine the validity of a succession of variously analytical, quasi-analytical, and numerical models now to be described.; In the non-experimental phase of the work, numerically assisted, exact solutions were obtained for the radiative heat transfer to the thermal load. Also, three-dimensional, laminar and turbulent numerical solutions for natural convection were carried out, with account being taken of the actual equation of state of the air within the oven and of the continuous heating at the walls and the discrete heating at the electric heater. These fundamental solutions were augmented with a number of quasi-analytical, differential and algebraic models. All of the aforementioned models were employed to predict the experimental data collected during the course of this investigation. The comparisons between the various predictions and the data were, in all cases, excellent and supported the validity of the models and the competence of the experimental technique.