AUGMEN TATION OF FREE CONVECTION HEAT TRANSFER THROVGH CYLINDRICAL ANNULUS

Abstract

In the present work, natural convection heat transfer through vertical cylindrical annulus is experimentally investigated. The inner cylinder is heated electrically with constant heat flux, while the outer one is subjected to ambient air. The out side Rayleigh number was varied between 80 and 1500 throughout this investigation. The aspect ratio is 50 while the radius ratio is I. 5. The annular gap is provided with helical-wire-coil rings wound around the outer surface of the inner cylinder as an augmentation device. The helical-wire-coil rings used are made of copper wire of different wire diameters. The wire is coiled around rods of different diameters in order to have helical-coils of different outside diameters. The helical-wire-coils are then wounded around the inner cylinder of the annulus in the form of rings with constant longitudinal distance along the axis of the annulus (ring pitch).