Abstract
The present study deals with the numerical simulation of mixed convective heat transfer from an unconfined heated square cylinder using nanofluids (Al2O3-water) for Reynolds number (Re) 10–150, Richardson number (Ri) 0–1, and nanoparticles volume fractions (φ) 0–5%. Two-phase modelling approach (i.e., Eulerian-mixture model) is adopted to analyze the flow and heat transfer characteristics of nanofluids. A square cylinder with a constant temperature higher than that of the ambient is exposed to a uniform flow. The governing equations are discretized and solved by using a finite volume method employing the SIMPLE algorithm for pressure–velocity coupling. The thermo-physical properties of nanofluids are calculated from the theoretical models using a single-phase approach. The flow and heat transfer characteristics of nanofluids are studied for considered parameters and compared with those of the base fluid. The temperature field and flow structure around the square cylinder are visualized and compared for single and multi-phase approaches. The thermal performance under thermal buoyancy conditions for both steady and unsteady flow regimes is presented. Minor variations in flow and thermal characteristics are observed between the two approaches for the range of nanoparticle volume fractions considered. Variation in φ affects CD when Reynolds number is varied from 10 to 50. Beyond Reynolds number 50, no significant change in CD is observed with change in φ. The local and mean Nusselt numbers increase with Reynolds number, Richardson number, and nanoparticle volume fraction. For instance, the mean Nusselt number of nanofluids at Re = 100, φ = 5%, and Ri = 1 is approximately 12.4% higher than that of the base fluid. Overall, the thermal enhancement ratio increases with φ and decreases with Re regardless of Ri variation.
Highlights
Nanofluids are the engineered colloidal suspension of nanosized particles (10–100 nm) in a base fluid [1]
Nusselt number of nanofluids at Reynolds number (Re) = 100, φ = 5%, and Richardson number (Ri) = 1 is approximately 12.4% higher than that of the base fluid
Mixed convective heat transfer from a heated square cylinder placed in a uniform flow is studied numerically with Al2O3-water nanofluids as the working fluid using the two-phase mixture model
Summary
Nanofluids are the engineered colloidal suspension of nanosized particles (10–100 nm) in a base fluid [1]. They have greater thermal conductivity compared to their base fluids and are considered smart fluids because the heat transfer rates can be controlled to some extent by varying nanoparticle concentration in the base fluid [2]. Nanofluids find applications in nuclear reactors [3], electronic cooling [4], heat exchanger [5], heating buildings in cold regions [6], drying of various materials [7], and automotive applications [8,9].
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