Abstract
The heat transfer process takes place in numerous applications through the natural convection of fluids. Investigations of the natural convection heat transfer in enclosures have gained vital importance in the last decade for the improvement in thermal performance and design of the heating/cooling systems. Aspect ratios (AR=height/length) of the enclosures are one of the crucial factors during the natural convection heat transfer process. The investigated fluids consisting of air, water, engine oil, mercury, and glycerine have numerous engineering applications. Heat transfer and fluid flow characteristics are studied in 3-dimensional rectangular enclosures with varying aspect ratios (0.125 to 150) using computational fluid dynamics (CFD) simulations. Studies are carried out using the five different fluids having Prandtl number range 0.01 to 4500 in rectangular enclosures with the hot and cold surface with varying temperature difference 20K to 100K. The Nusselt number and heat transfer coefficients are estimated at all conditions to understand the dependency of ARs on the heat transfer performance of selected fluids. Temperature and velocity profiles are compared to study the flow pattern of different fluids during natural convection. The Nusselt number correlations are developed in terms of aspect ratio and Rayleigh number to signify the natural convection heat transfer performance.
Highlights
The mechanism of heat transfer persuaded by buoyancy force, which causes movement of fluid due to change in density by temperature gradient, is known as natural convection
Heat transfer and fluid flow characteristics are studied in 3-dimensional rectangular enclosures with varying aspect ratios (0.125 to 150) using computational fluid dynamics (CFD) simulations
A generic Nusselt number correlation is proposed for different fluids, which is based on the simulated results
Summary
The mechanism of heat transfer persuaded by buoyancy force, which causes movement of fluid due to change in density by temperature gradient, is known as natural convection. Arici et al [17] investigated heat transfer and fluid flow characteristics in double, triple and quadruple pane windows for a variety of aspect ratios and temperature gradients In their numerical study, they observed that gap width is an important energy-saving factor, and the effect is more noticeable at lowtemperature gradients. Ganguli et al [18] investigated the heat transfer behavior of air during natural convection across cold and hot surfaces in enclosed rectangular geometries with a wide range of aspect ratios. This research presents the investigation of natural convection behavior of different crucial heat transfer fluids, i.e., air, water, engine oil, mercury, and glycerine. These fluids are encountered in numerous engineering applications. A generic Nusselt number correlation is proposed for different fluids, which is based on the simulated results
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