What is it about?
Porous materials are widely used in heat exchangers and energy storage systems to transfer and retain thermal energy efficiently. However, in real-world manufacturing or over long periods of operation, the solid surfaces inside these materials develop microscopic roughness due to fabrication limits, corrosion, or scale deposition. In this paper, we used detailed computer simulations to examine how turbulent fluid flow and heat transfer change when square surface bumps are explicitly added onto the solid obstacles within a porous material. Our research demonstrates that the physical height and spacing of these surface bumps fundamentally reshape how fluid flows around the obstacles. Very small, tightly spaced roughness particles trap fluid inside tiny cavities, forming an insulating fluid layer that reduces overall heat transfer compared to smooth obstacles. Conversely, larger or more widely spaced roughness elements disrupt the fluid layer and entrain cooler fluid, which enhances heat transfer but simultaneously increases fluid resistance and drag.
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Why is it important?
Most existing research on transport in porous media assumes idealized, perfectly smooth solid obstacles or focuses strictly on low-speed laminar flows in geological contexts. Our paper fills a major gap by presenting a systematic study of turbulent convection around rough obstacles across multiple porosity levels and flow speeds. By analyzing the underlying microscale flow patterns, we resolve conflicting observations in literature regarding whether surface roughness helps or hurts thermal performance. These findings are particularly timely for engineers designing high-performance heat exchangers and thermal energy storage devices needed for renewable energy systems. Recognizing the precise conditions under which roughness degrades or improves heat transfer enables designers to set realistic manufacturing tolerances, predict long-term performance degradation, or deliberately design surface textures that optimize thermal performance without incurring severe pumping penalties.
Perspectives
Collaborating with my co-author, Vishal Srikanth, on this project was a rewarding effort in connecting microscale fluid dynamic phenomena to macroscopic thermal performance. It was remarkable to observe how tiny recirculating vortices—occupying just a small fraction of the obstacle size—can dictate whether an entire porous heat exchanger experiences thermal insulation or enhanced cooling. I hope this paper encourages the thermal science community to look beyond idealized smooth geometries when modeling porous systems. Accounting for realistic microscale surface textures is a crucial step toward building accurate predictive models and developing innovative passive heat transfer enhancement techniques for clean energy applications.
Andrey V Kuznetsov
North Carolina State University
Read the Original
This page is a summary of: NUMERICAL INVESTIGATION OF TURBULENT CONVECTION HEAT TRANSFER IN POROUS MEDIA COMPOSED OF ROUGH SOLID OBSTACLES, January 2023, Begell House,
DOI: 10.1615/ihtc17.370-50.
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