Enhancement of laminar convective heat transfer relying on excitation of transverse secondary swirl flow

Abstract

Laminar forced convective heat transfer is studied for the purpose of getting the best heat transfer performance with the least flow resistance increase. The variation calculus method is employed to establish the equations describing the optimized fluid velocity field and temperature field. Numerical solutions of the equations for a convective heat transfer process in a section-cut of a square duct indicate the optimized flow should have a transverse secondary swirl flow pattern consisting of multiple vortexes with identical swirl direction in the junction region of any two neighboring vortexes. We then propose the convective heat transfer enhancement method relying on excitation of transverse secondary swirl flow. To validate this method, we numerically study the heat transfer and flow resistance characteristics of laminar flows in tubes with four-reverse-vortex-generator (FRVG) inserts, four-homodromous-vortex-generator (FHVG) inserts, or a twisted tape insert. The calculated transverse secondary flow in the tube with the FRVG inserts approximately follows the optimized flow pattern and the tube is thus found to have the best thermo-hydraulic performance, validating the proposed convective heat transfer enhancement method.