Numerical investigation on two-phase oscillating flow and heat transfer enhancement for a cooling channel with ribs

Rib structures can enhance heat transfer in single-phase flows. In order to investigate the influence of semi-circular rib structures on the two-phase oscillating flow and heat transfer characteristics, two-dimensional computational fluid dynamics (CFD) models were established for the cooling channels with rib diameters of 2, 4, 6, and 8 mm. The shear stress transportation (SST) k-omega turbulence model and the Volume of Fluid (VOF) symbolscript-Set model were used to simulate the flow pattern and predict the two-phase flow interface. A visual experiment was performed to validate the CFD models. The results showed that during the reciprocating motion of the channel, both sides of the rib were impinged and flushed continuously by the cooling oil. Therefore, the heat transfer on the both sides of the rib was enhanced, and the peak value of the heat transfer coefficient (HTC) increased by 100.5% when the rib diameter was 2 mm compared to the channel without ribs. The rib diameter increase had little influence on the peak value of the cycle-average HTC near the rib and the left wall. However, the oil flow velocity on the flat wall and the impingement intensity on the top wall were weakened due to the rib structure, resulting in a reduction in the cycle-average HTCs of the flat wall and the top wall. Furthermore, the larger the rib diameter, the more reduction in the cycle-average HTCs of the flat wall and the top wall. When the rib diameter was 8 mm, the reductions in the cycle-average HTCs on the flat wall and the top wall were the most obvious, reaching 10.7% and 8.3%, respectively. The numerical results in this study can provide design guidance for heat transfer enhancement of cooling channels during reciprocating motions.