Natural convection in vertical, parallel-plate channels with appended unheated entrances

Purpose - To address the impact of adding insulated plate extensions at the entrance of an isoflux vertical parallel-plate channel on the thermal performances of natural convection in air for these systems. Design/methodology/approach - The model relies on the full elliptic conservation equations which are solved numerically in a composite three-part computational domain by means of the finite-volume method. Findings - Results are reported in terms of wall temperatures, induced mass flow rates, as well as velocity and temperature profiles of the air for various thermal and geometric parameters. The wall temperatures increase when the extensions are appended at the inlet of the channel. Wall temperature profiles strongly depend on the Rayleigh number and the dependence of the heated channel aspect ratio is weaker than the extension ratio. Velocity and temperature profiles modify inside the heated channel due to the thermal development. In addition, correlation equations for main engineering quantities, such as the induced mass flow rate, average Nusselt number and dimensionless maximum wall temperature in terms of the channel Rayleigh number, channel aspect ratio and extension ratio are presented. Research limitations/implications - The investigation has been carried out in the following ranges: 10(3)-10(5) for the Rayleigh number, 5.0-15.0 for the channel aspect ratio and 1.0-5.0 for the extension ratio. The hypotheses on which the present analysis is based are: two-dimensional, laminar and steady-state flow, constant thermophysical properties with the Boussinesq approximation. Practical implications - Thermal design of heating systems in manufacturing processes, evaluation of heat convective coefficients and maximum attained wall temperatures. Originality/value - Evaluation of the thermal and velocity fields and correlation equations for the Nusselt number and maximum dimensionless temperatures in natural convection in air for vertical channels. The paper is useful to thermal designers.