Experimental and numerical investigation of heat and fluid flow in a square duct featuring criss-cross rib patterns

This paper presents findings from experimental and numerical study of heat and fluid flow in a straight square duct featuring rib turbulators in a criss-cross pattern formed by 45° angled rib turbulators. Two ribbed configurations with criss-cross pattern - Inline and staggered, have been studied where the baseline case was smooth duct with no heat transfer enhancement feature. Detailed heat transfer coefficients were calculated using transient liquid crystal thermography by employing 1-D semi-infinite conduction model. Heat transfer and pressure drop measurements were carried out for Reynolds number ranging from 30,000 to 60,000. For understanding of heat transfer enhancement mechanism, numerical investigations were carried out using SST k-ω turbulence model. Numerical predictions of near-wall fluid dynamics and turbulent transport has been presented in conjunction with experimentally obtained detailed heat transfer coefficients to demonstrate the heat transfer characteristics of ribbed duct. Nusselt numbers normalized with respect to Dittus-Boelter correlation for developed turbulent flow in circular duct varied between 2.7 and 3.1 for inline and staggered configurations and the thermal hydraulic performance varied between 1.2 and 1.5 for the range of Reynolds number investigated.