The enhancement of the thermal performance of heat exchanging equipment transport energy at low financial cost by various techniques is presented in this review. Various annular passage configurations have been used in the reviewed studies, namely circular, ellipse, rectangular, square, triangular, and rhombic annular channels with different fluid and boundary conditions. The effect of eccentricity in both horizontal and vertical directions on heat transfer rate in most numerical and experimental investigations for horizontal and vertical annular passages is studied. The effects of heater length, as well as the Darcy, Prandtl, Reynolds, Grashof and Rayleigh numbers on heat transfer in concentric and eccentric annular passages are also investigated. In case of rotating the inner, outer or both cylinders of the annular cylinder arrangement, the generated secondary flow influences the heat transfer to fluid flow in an annular passage. The effect of nanofluid on the increased enhancement of heat transfer in an annular channel is presented. Related studies on curved, covered annular channels showed augmented heat transfer rate in comparison with straight annular channels. In this review, a good agreement is evident between experimental and numerical data, which could help researchers design thermal systems supported by annular passages with the goal of retarding energy consumption by equipment and machineries in applications that could ultimately contribute to appeasing the global energy crisis.

A review of studies on forced, natural and mixed heat transfer to fluid and nanofluid flow in an annular passage.

This work deals with the cooling of high-speed electric machines, such as motors and generators, through an air gap. It consists of numerical and experimental modeling of gas flow and heat transfer in an annular channel. Velocity and temperature profiles are modeled in the air gap of a high-speed test machine. Friction and heat transfer coefficients are presented in a large velocity range. The goals are reached acceptably using numerical and experimental research. The velocity field by the numerical method does not match in every respect the estimated flow mode. The absence of secondary Taylor vortices is evident when using time averaged numerical simulation.

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Numerical and experimental modelling of gas flow and heat transfer in the air gap of an electric machine

The study of heat transfer by forced convection in annular passages is of interest across the range of process and aeronautical industries, for example from annular heat exchangers to the various configurations of annuli found in turbomachinery. The aim of this paper is to review relevant experimental, numerical and analytical research of heat transfer in both stationary and rotating annuli, with an emphasis on presenting useful information for designers. The geometries considered are the stationary annulas with superposed axial throughflow and the rotating annulus with rotation of either the inner or outer cylinder (both with and without throughflow). The work presented covers laminar and turbulent flows as well as flow regimes where transition occurs or vortex flows are present.

A Review of Forced Convective Heat Transfer in Stationary and Rotating Annuli

Mixed convection within a porous heat generating horizontal annulus

Numerical results are presented for two-dimensional laminar mixed convection flows around a heated horizontal square cylinder rotating slowly within a concentric circular enclosure. The time evolution of the rotation and buoyancy-induced mixed convection flows are analyzed over a range of the radius ratio χ, the Gr, and the rotational Re. The radius ratio considered ranged from 0.2 to 0.55. The Gr range is taken from 103 to 2 × 104, and the rotational Re varied from 0 to 24. The flow and temperature fields and heat transfer characteristics are presented over this parameter range. The effect of the rotating noncircular geometry of the inner cylinder on the flow field and the heat transfer characteristics are considered in detail and compared with those previously studied for differentially heated concentric circular annuli.

Yang Lei

Papers

Three-dimensional mixed convection flows in a horizontal annulus with a heated rotating inner circular cylinder

Experimental study on pressure transfer mechanism of magnetic fluid seal in the vacuum environment