Convective heat transfer enhancement: effect of multi-frequency heating

Purpose This study aims to enhance natural convection heat transfer for a porous thermal cavity. Multi-frequency sinusoidal heating is applied at the bottom of a porous square cavity, considering top wall adiabatic and cooling through the sidewalls. The different frequencies, amplitudes and phase angles of sinusoidal heating are investigated to understand their major impacts on the heat transfer characteristics. Design/methodology/approach The finite volume method is used to solve the governing equations in a two-dimensional cavity, considering incompressible laminar flow, Boussinesq approximation and Brinkman-Forchheimer-Darcy model. The mean-temperature constraint is applied for enhancement analysis. Findings The multi-frequency heating can markedly enhance natural convection heat transfer even in the presence of porous medium (enhancement up to similar to 74 per cent). Only the positive phase angle offers heat transfer enhancement consistently in all frequencies (studied). Research limitations/implications - The present research idea can usefully be extended to other multi-physical areas (nanofluids, magneto-hydrodynamics, etc.). Practical implications - The findings are useful for devices working on natural convection. Originality/value The enhancement using multi-frequency heating is estimated under different parametric conditions. The effect of different frequencies of sinusoidal heating, along with the uniform heating, is collectively discussed from the fundamental point of view using the average and local Nusselt number, thermal and hydrodynamic boundary layers and heatlines.