The influence of the wall temperature on the development of heat transfer and secondary flow in a coiled heat exchanger

In the present study the development of mixed convective flow is studied in a helically coiled heat exchanger with an axially varying wall temperature for Re = 500, Pr = 5 and delta = 1/14 and compared to the constant wall te mperature boundary condition. In the method used the parabolized equations are solved using a finite difference discretization scheme. The influence o f buoyancy forces is analyzed on heat transfer and secondary how. For all G rashof numbers studied it appears that both heat transfer, quantified by th e Nusselt number, and secondary flow, quantified by the relative kinetic en ergy, exhibit a wavy behaviour in axial direction. For higher Grashof numbe rs, however, this phenomenon diminishes for the case with an axially varyin g wall temperature due to stabilizing stratification effects. (C) 1999 Else vier Science Ltd.