Abstract
The thermal fluidynamic behaviour of a variety of fluids filling either vertical cylinders or vertical annuli under external conditions giving rise to natural convective motions has been thoroughly investigated, both experimentally and numerically, because of the several possible engineering applications that can be well approximated and described by these kinds of configurations. This study aims at investing through a numerical analysis the mixed convection arising inside cavities formed between two horizontal adiabatic disks and two isothermally and differentially heated vertical cylindrical walls, one of which is rotating. Previous studies reported and discussed the role played by both the Rayleigh number the Reynolds number for the case of the rotation of either the inner or the external wall and for a specified geometry of the cavity. The focus of the present study is to analyse the role played by the aspect ratio, A=H/(Re-Ri), for the case of rotating inner cylinder. It is reported that this role is particular relevant with respect to the flow structures established within the cavity and, as a consequence, also with respect to the Nusselt number.
Highlights
The natural convection of a fluid in an annulus between two vertical rotating concentric cylinders is a topic of major interest in many fields of applications, such as electrical machineries, thermal energy storage systems and chemical mixing equipment
The mixed convection of a fluid of Pr=5 within a vertical annular enclosure with isothermally heated and cooled vertical walls was simulated for the case of rotation of the inner wall
This is reflected in the reduction of the size of the counter-rotating cell at the inner rotating wall that can be observed for growing aspect ratio, until A=4, and its disappearance for A=8, where the buoyancy-generates cell occupies the entire enclosure
Summary
The natural convection of a fluid in an annulus between two vertical rotating concentric cylinders is a topic of major interest in many fields of applications, such as electrical machineries, thermal energy storage systems and chemical mixing equipment. Some interest has been focused on the analysis of “buoyancy dominated flows”, i.e. natural convective flows that are generated in static systems. Example of this are the studies of Vahl Davis and Thomos [1] and Kumar and Kalman [2], where correlations between the number of Nusselt and physical parameters have been determined. Other works deal with the dynamical contribution occurring in vertical annular cavity in which one (or both) of the walls, either of the cylinder or of the annulus, rotates. [5] proposed a numerical study to evaluate the influence of the Prandtl number on the flow and the heat transfer rate on a rotating cylindrical annulus Urquiza et alii. [5] proposed a numerical study to evaluate the influence of the Prandtl number on the flow and the heat transfer rate on a rotating cylindrical annulus
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