Analytical Solution of Natural Convection Flow in Vertical Concentric Annuli with Internal Heat Generation/Absorption † Basant K. Jha and Abiodun O. Ajibade Department of Mathematics, Ahmadu Bello University Zaria, Nigeria E-mail: olubadey2k@yahoo.com Equations governing the steady, laminar fully developed natural convection flow in vertical concentric annuli in presence of temperature dependent heat sources/sinks are developed. These equations are solved analytically in terms of modified Bessel’s functions subject to the appropriate conditions. In the present analysis, convection current is setup due to the temperature difference between the outer surface of the inner cylinder and inner surface of the outer cylinder as well as the presence of heat sources or sinks in the system. Expressions for veloc- ity field, temperature field, mass flow rate and skin-friction (at the outer surface of inner cylinder and inner surface of the outer cylinder) are obtained in terms of modified Bessel’s function. *** Nomenclature a radius of inner cylinder; b radius on outer cylinder; g acceleration due to gravity; k thermal conductivity of fluid; Q 0 strength of heat source/sink in dimensional form; r ′ radial coordinate; R non-dimensional radial coordinate; S 2 strength of heat source/sink in dimensionless form; T ′ temperature of fluid in dimensional form; T temperature of fluid in dimensionless form; T ′ w temperature of outer surface of inner cylinder; T ′ ∞ temperature of inner surface of outer cylinder; u ′ velocity of fluid in dimensional form along z ′ -axis; U velocity of fluid in dimensionless form. † Received 08.02.2011 373 ISSN 1064-2277 c  2012 Begell House, Inc.