Thermal management in viscoplastic systems: on the role of heat source configuration and yield number

This study numerically investigates the influence of heat-source configuration—concentrated versus distributed—on Rayleigh-Bénard convection in a viscoplastic fluid within a square enclosure. Utilizing the Bingham model, the governing conservation equations are solved via the Galerkin Finite Element Method across a range of Rayleigh numbers ( 10 5 ≤ Ra ≤ 10 6 ) and Yield numbers (0 ≤ Y ≤ Y max ). The primary objective is to evaluate the impact of the spatial distribution of heating on flow structures, unyielded regions, and overall heat-transfer efficiency. The results reveal a paradoxical thermal performance: contrary to the well-established principle for Newtonian fluids, where distributed heating enhances heat transfer, a concentrated heat source yields consistently superior overall heat transfer rates in viscoplastic fluids. This thermal advantage of the concentrated source is significantly amplified at higher Rayleigh numbers. Furthermore, analysis of the flow topology indicates that the concentrated source generates a single, powerful buoyant plume capable of driving a vigorous, large-scale circulation. In contrast, distributed sources fail to organize the flow into a coherent global structure, resulting in weaker overall convection despite locally fluidizing the material near the heaters. Finally, the concentrated heating configuration demonstrates enhanced convective stability, sustaining fluid motion over a wider range of fluid plasticity compared to the distributed setup. These counterintuitive findings carry significant practical implications, suggesting that a targeted, concentrated heating strategy is far more effective for the thermal management of rheologically complex fluids in industries such as polymer processing and food manufacturing. • Numerical study compares concentrated and distributed heating in Rayleigh. • Bénard viscoplastic convection. • Concentrated heating forms a coherent plume and stronger global circulation • Thermal benefits of concentrated heating increase at higher Rayleigh numbers. • Concentrated heating sustains convection at higher Yield numbers and fluid plasticity.