FLUID FLOW AND HEAT TRANSFER CHARACTERISTICS OF NON-CIRCULAR ANNULAR PASSAGES

Abstract

The design and development of compact passages for heat exchangers, inclUding those in.nuclear reactor Cores, depends critically on the knowledge of the local flow and heat transfer characteristics. It has been found that non-circular ducts improve the performance of heat exchangers making them compact and efficient. In the present work, fluid flow and heat transfer characteristics of the non-circular annular passages bounded externally by a circle and internally by a regular polygon are investigated both analytically and experimentally. Hydrodynamically and thermally developed, steady, laminar flow of a constant property fluid has been investi-gated analytically. The thermal boundary conditions of the second kind i.e. insulated outer tube and constant heat flux at the inner wall have been considered. Finite element solution algorithm has been developed for obtaining numerical solutions to the governing equations for momentum and energy transfer. Detailed results' for velocity and temperature profiles have been obtained for the annuli with an inner core of each one of the following crass-sections: (i) equilateral triangle (ii) square (iii) hexagon (iv) octagon (v) eighteen-sided polygon and (vi) circle (i.e. circular annulus). The friction factors at the inner and at the outer walls, the average friction factor and the Frusselt number have been evaluated. The investigation covers the range of aspect ratio from 0.02 to 0.999 for each configuration of the annuli...