Comparative study of flow structures and heat transfer enhancement in a metallic lattice fabricated by metal sheet folding: Effects of punching location shift

Abstract

This study numerically investigates the effects of the punching location shift on thermo-fluidic characteristics of a metallic lattice fabricated by the metal sheet folding method. By shifting the punching location, new lattices with the identical porosity and surface area density can be fabricated without redesigning the metal sheet or adjusting the fabrication process. The effects of the punching location shift on the flow and heat transfer is totally different when the dimensionless punching location shift (s/d) is below and above 0.55, respectively. When s/d is below 0.55, the flow is composed of the parallel primary flow and the counter-rotating vortex pair; the average overall Nusselt number increases with the increase of s/d; and both the primary and secondary flows are responsible for the enhanced heat transfer. When s/d is above 0.55, the spiral primary flow and three kinds of secondary flows (i.e., two types of cross-flows and a counter-rotating vortex pair downstream each ligament) dominate the fluid flow behaviors; the average overall heat transfer varies slightly and tends to decline when s/d is above 0.8; and the variation in the secondary flows result in the corresponding heat transfer variation. When s/d is 0.55–0.8, the average overall Nusselt number approximately remains constant and is about 10% higher than that of the ideal X-lattice. The variation of the friction factor as a function of s/d resembles that of the local heat transfer on ligaments because pressure drop is dominated by the form drag induced by ligaments. The overall thermal performance ranked from the inferior to the superior is as follows: the pyramidal lattice (s/d = 0), the lattice with a quarter punching location shift (s/d = 0.25), the X-lattice (s/d = 1) and the other lattices.