Air-Gap Convection in Rotating Electrical Machines

This paper reviews the convective heat transfer within the air gap of both cylindrical and disk geometry rotating electrical machines, including worked examples relevant to fractional horsepower electrical machines. Thermal analysis of electrical machines is important because torque density is limited by maximum temperature. Knowledge of surface convective heat transfer coefficients is necessary for accurate thermal modeling, for example, using lumped parameter models. There exists a wide body of relevant literature, but much of it has traditionally been in other application areas, dominated by mechanical engineers, such as gas turbine design. Particular attention is therefore given to the explanation of the relevant nondimensional parameters and to the presentation of measured convective heat transfer correlations for a wide variety of situations from laminar to turbulent flow at small and large gap sizes for both radial-flux and axial-flux electrical machines.

[1]  S. Harmand,et al.  Local convective heat transfer for laminar and turbulent flow in a rotor-stator system , 2005 .

[2]  Joseph Kaye,et al.  Measurements of Diabatic Flow in an Annulus With an Inner Rotating Cylinder , 1962 .

[3]  Peter R.N. Childs.  Flow in rotating components - discs, cylinders and cavities , 2007 .

[4]  P. Childs,et al.  Heat Transfer to a Rotating Drum in an Annulus with a Stator Blade Row and Axial Throughflow , 1992 .

[5]  Andrea Cavagnino,et al.  Convection Heat Transfer and Flow Calculations Suitable for Electric Machines Thermal Models , 2008, IEEE Transactions on Industrial Electronics.

[6]  Andrew S. Holmes,et al.  Prediction and measurement of heat transfer in air-cooled disc-type electrical machines , 2010 .

[7]  A. B. Turner,et al.  Heat 'Transfer on the Surface of a Cylinder Rotating in an Annulus at High Axial and Rotational Reynolds Numbers , 1994 .

[8]  L. Rayleigh.  On the Dynamics of Revolving Fluids , 1917 .

[9]  Sébastien Poncet,et al.  Batchelor versus Stewartson flow structures in a rotor-stator cavity with throughflow , 2005 .

[10]  K. Stewartson.  On the flow between two rotating coaxial disks , 1953, Mathematical Proceedings of the Cambridge Philosophical Society.

[11]  S. Wittig,et al.  Local Heat Transfer in Turbine Disk-Cavities: Part I — Rotor and Stator Cooling With Hub Injection of Coolant , 1990 .

[12]  G. Batchelor.  NOTE ON A CLASS OF SOLUTIONS OF THE NAVIER-STOKES EQUATIONS REPRESENTING STEADY ROTATIONALLY-SYMMETRIC FLOW , 1951 .

[13]  P. Childs,et al.  A Review of Forced Convective Heat Transfer in Stationary and Rotating Annuli , 1996 .

[14]  A.C. Smith,et al.  Assessment of power losses of an inverter-driven induction machine with its experimental validation , 2002, Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344).

[15]  R. E. Nece,et al.  Chamber Dimension Effects on Induced Flow and Frictional Resistance of Enclosed Rotating Disks , 1960 .

[16]  C. J. Scott,et al.  Turbulent Heat Transfer Studies in Annulus With Inner Cylinder Rotation , 1975 .

[17]  Sébastien Poncet,et al.  Centrifugal Flow in a Rotor-Stator Cavity , 2005 .

[18]  J. Owen,et al.  Heat transfer from an air-cooled rotating disk , 1974, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[19]  G. Taylor.  Stability of a Viscous Liquid Contained between Two Rotating Cylinders , 1923 .

[20]  J. M. Owen,et al.  Flow and Heat Transfer in Rotating Disc Systems, Vol.1: Rotor-Stator Systems , 1989 .

[21]  K. Becker,et al.  The Influence of a Radial Temperature Gradient on the Instability of Fluid Flow in an Annulus With an Inner Rotating Cylinder , 1962 .

[22]  L. A. Dorfman,et al.  Hydrodynamic resistance and the heat loss of rotating solids , 1963 .

[23]  J. M. Owen,et al.  Flow and heat transfer in rotating-disc systems , 1994 .

[24]  Alessandro Giua,et al.  Guest Editorial , 2001, Discrete event dynamic systems.

[25]  Aldo Boglietti,et al.  Special section on thermal issues in eletrical machines and drives , 2008 .

[26]  T. Kármán.  Über laminare und turbulente Reibung , 1921 .

[27]  D. R. Turner,et al.  Lumped parameter thermal model for electrical machines of TEFC design , 1991 .

[28]  W. Kays,et al.  Heat transfer between concentric rotating cylinders , 1959 .

[29]  E. C. Cobb,et al.  Heat transfer from a rotating disk , 1956, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[30]  K. Pullen,et al.  Radially resolved measurement of stator heat transfer in a rotor-stator disc system , 2010 .

[31]  E. Spooner,et al.  TORUS' : a slotless, toroidal-stator, permanent-magnet generator , 1992 .

[32]  Jacek F. Gieras,et al.  Axial Flux Permanent Magnet Brushless Machines , 2005 .

[33]  Keith Robert Pullen,et al.  An investigation into the flow within inclined rotating orifices and the influence of incidence angle on the discharge coefficient , 2004 .

[34]  A. Boglietti,et al.  Solving the more difficult aspects of electric motor thermal analysis in small and medium size industrial induction motors , 2005, IEEE Transactions on Energy Conversion.

[35]  J.E.R. Coney,et al.  A Reynolds analogy solution for the heat transfer characteristics of combined Taylor vortex and axial flows , 1979 .

[36]  J. Owen.  The Reynolds analogy applied to flow between a rotating and a stationary disc , 1971 .

[37]  Andrea Cavagnino,et al.  Evolution and Modern Approaches for Thermal Analysis of Electrical Machines , 2009, IEEE Transactions on Industrial Electronics.