Free convection with MWCNT/water nanofluid having varying aspect ratio of MWCNT nanoparticle in thermally undulated enclosures

The Aspect ratio of carbon nanotubes (CNTs) in cavities of different geometrical aspect ratio is one of the critical parameters of the design in thermal engineering. The present work documented a numerical simulation of 2D, steady and laminar free convection in rectangular cavities with different aspect ratios filled with water-based nanofluid. The nanoparticle considers in the present work is MWCNT with varying average diameter and length consequently varying aspect ratio. The Navier-Stokes and energy equations are solved numerically, coupling Thang a al. [43] model for calculating the effective thermal conductivity and Brenner and Condiff [44] model for determining the effective dynamic viscosity. The results are presented in the form of streamlines, isotherms, vertical velocity and Nusselt numbers. The novelty of the present study is to find the effect of MWCNT nanoparticle aspect ratio on fluid flow and heat transfer. Maximum of about 65% increment in average Nusselt number is observed at maximum aspect ratio (length/diameter) of 6 x 10(4) for any temperature undulation and cavity aspect ratio. Maximum MWCNT aspect ratio (or minimum diameter) is proposed for better heat transfer. A range of Rayleigh number is observed for better heat transfer for different temperature undulation value at the left wall.