Analysis of natural convection for a Casson-based multiwall carbon nanotube nanofluid in a partially heated wavy enclosure with a circular obstacle in the presence of thermal radiation.

INTRODUCTION: Nanofluids are considered a better alternative to conventional fluids in many industrial situations and unfolding new opportunities for various applications owing to the optical and thermal properties of additive nanosized materials. OBJECTIVES: In this study, the thermal and hydraulic characteristics of a Casson-based (sodium alginate) multiwall carbon nanotube (MWCNT) nanofluid were computationally investigated inside a wavy square enclosure containing a circular-shaped obstacle. The square enclosure comprised two cooled vertical walls and a wavy adiabatic top wall. The central part of the bottom wall comprised a heated wavy structure, and the remaining parts exhibited a flat and adiabatic structure. METHODS: The Navier-Stokes (N-S) equations and boundary conditions were established using the non-Newtonian Casson fluid model and Rosseland thermal radiation. The present problem was numerically simulated using the Galerkin finite element method for three types of obstacles, namely, adiabatic, hot, and cold. The impacts of Casson parameter (0.001 ≤ ß ≤ 0.1), Rayleigh number (103 ≤ Ra ≤ 106), nanoparticle volume fraction (0.01 ≤ φ ≤ 0.1) and radiation parameter (1 ≤ Rd ≤ 4) are analysed. A numerical code validation was performed using the available benchmark results. RESULTS: The characteristics of the convective radiation heat transport were clearly analyzed through the stream function and isotherm plots. For all types of obstacles, the mean Nusselt number along the heated wavy wall increased with the Casson parameter, MWCNT volume fraction, Rayleigh number, and radiation parameter. CONCLUSION: The heat and flow characteristics of a Casson-based MWCNT nanofluid inside a wavy square enclosure were investigated. The mean Nusselt number was higher (lower) in the presence of cold (hot) obstacles.

Flow of hybrid nanofluid across a permeable longitudinal moving fin along with thermal radiation and natural convection.

BACKGROUND: The numerical investigation of nanoparticles embedded water based hybrid nanoliquid flow over porous longitudinal fin moving with constant velocity is carried out together with thermal radiation and natural convection condition. Darcy's model is implemented for the flow behaviour. The two types of boundary conditions are considered at the tip i.e., insulated tip fin and fin with known convective condition. METHOD: The modelled ordinary differential equation is non-dimensionalized and tackled mathematically by applying RKF (Runge Kutta Fehlberg) technique. RESULTS: The parametric evaluation is carried out through graphs and interpreted physically. From obtained outcomes, it is noticed that, fin with known convective coefficient at the tip shows greater heat transfer rate than fin with insulated tip.

Numerical study of entropy generation due to coupled laminar and turbulent mixed convection and thermal radiation in an enclosure filled with a semitransparent medium.

The effect of radiation on laminar and turbulent mixed convection heat transfer of a semitransparent medium in a square enclosure was studied numerically using the Finite Volume Method. A structured mesh and the SIMPLE algorithm were utilized to model the governing equations. Turbulence and radiation were modeled with the RNG k-ε model and Discrete Ordinates (DO) model, respectively. For Richardson numbers ranging from 0.1 to 10, simulations were performed for Rayleigh numbers in laminar flow (104) and turbulent flow (108). The model predictions were validated against previous numerical studies and good agreement was observed. The simulated results indicate that for laminar and turbulent motion states, computing the radiation heat transfer significantly enhanced the Nusselt number (Nu) as well as the heat transfer coefficient. Higher Richardson numbers did not noticeably affect the average Nusselt number and corresponding heat transfer rate. Besides, as expected, the heat transfer rate for the turbulent flow regime surpassed that in the laminar regime. The simulations additionally demonstrated that for a constant Richardson number, computing the radiation heat transfer majorly affected the heat transfer structure in the enclosure; however, its impact on the fluid flow structure was negligible.