Experimental investigation of Rayleigh-Bénard convection patterns in low-concentration nanofluids

This study investigates the influence of titanium dioxide ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>TiO</a:mi> <a:mn>2</a:mn> </a:msub> </a:math> ) nanoparticles suspended in water on convection cells and heat transfer dynamics. To this end, a Rayleigh-Bénard experimental study was conducted for a water- <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msub> <b:mi>TiO</b:mi> <b:mn>2</b:mn> </b:msub> </b:math> nanofluid ( <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mo>&lt;</c:mo> <c:mn>0.02</c:mn> </c:math> % wt) in a cylindrical cavity with a diameter to height aspect ratio of 16. A shadowgraph was used to visualize the spatial and temporal evolution of convection cells in a Rayleigh regime ( <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:mo>&lt;</d:mo> <d:msup> <d:mn>10</d:mn> <d:mn>4</d:mn> </d:msup> </d:mrow> </d:math> ), well suited for observing transitions and stability in flow patterns. The observations show that both colloidal stability and nanoparticle sedimentation strongly affect the evolution of convection patterns and heat transfer. These experiments qualitatively demonstrate that <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:msub> <e:mi>TiO</e:mi> <e:mn>2</e:mn> </e:msub> </e:math> nanoparticles can enhance heat transfer under convective conditions, as inferred from the observed changes in convection cell pattern and flow organization. While nanofluids are typically designed to maximize colloidal stability, minimize agglomeration, and prevent sedimentation, our results challenge this paradigm by showing that sedimentation plays a key role in intensifying heat transport.