Fully developed forced convection through trapezoidal and hexagonal ducts

Laminar, fully developed flow through single- and double-trapezoidal (or he xagonal) ducts is modeled using a finite-difference method. A coordinate tr ansformation is employed to map the irregular flow cross-section onto a rec tangular computational domain. Both H1 and T thermal boundary conditions ar e considered as they represent the fundamental limiting conditions in most practical applications. Solutions for velocity and temperature variations a re obtained for a wide range of duct aspect ratios and with four different trapezoidal angles. The friction factor and Nusselt number results show a s trong dependence on duct geometry (aspect ratio gamma and trapezoidal angle theta). The variations off Re, Nu(H1), and Nu(T) With duct aspect ratio fo r each theta-valued duct are presented in the form of polynomials in gamma. These equations describe the computed numerical values within +/-2% for si ngle-trapezoidal and within +/-1.5% for hexagonal ducts and are of much imp ortance to the design of compact heat exchangers. (C) 1999 Elsevier Science Ltd. All rights reserved.