Aerothermal performance of two-pass channel with tilted grater-baffles

Abstract

Aerothermal performances of four two-pass channels enhanced by tilted 90° or 60° grater-baffles with one- or two-rows of perforation are studied. Aerothermal impacts of baffle attack angle and perforation row-number on Nusselt number (Nu) distribution, friction factor (f), and aerothermal performance index (API) are cross examined. Cold streams from duct core are confluent in oval dimples to eject through inclined grater-baffle as impinging jets that diminish boundary layers at stagnation spots and augment core-to-wall mixings, leading to significant heat transfer enhancements (HTE). Heat transfer data reveals that the HTE impact increases and decreases with perforation-row number and Reynolds number (Re) respectively. With the sectional vortical flows tripped by the 60° grater-baffles, both Nu and f are raised from those with the 90° baffles. The Nusselt numbers and friction factors for the two-pass channel enhanced by the inclined 60° baffles with two perforation rows are elevated to 4.64–4.95and 33.67–34.16 times Dittus-Boelter correlation and Blasius equation levels, giving rise to the API in the range of 1.67 and 1.43 at Re between 5000 and 15,000. Empirical correlations of regional average Nu and channel average f for the four two-pass baffled channels are devised to assist engineering applications.