Convective Regime Classification and Heat Transfer Characterization of Domestic Electric Ovens: Effect of Enamel Coating Thickness and Cavity Geometry on Natural Convection, Thermal Resistance, and Energy Efficiency Index

This study experimentally investigates the combined effects of enamel coating thickness and shelf geometry on the thermal performance and energy efficiency of domestic electric ovens. Four configurations were tested by varying enamel thickness and shelf design. All four configurations operate in the transition natural convection regime. Dimensionless analysis showed comparable Nusselt numbers between the wire-rack and embossed-rack geometries, indicating that internal convective heat transfer alone does not explain the superior energy class achieved by the embossed-rack configuration. Thermographic and thermocouple measurements instead show that geometric irregularities in the embossed surface promote localized heat accumulation, reducing heat loss to the exterior at the cost of less uniform internal temperature distribution. The enamel layer dominates the composite wall resistance, accounting for up to 93.5