Abstract
This study investigates the effect of acceleration and deceleration in the turn region of a two-pass, serpentine channel. Channel aspect ratios of 2:1 and 4:1 are considered in three combinations to investigate the effect of acceleration and deceleration through the turn region in a smooth, two-pass channel. For each aspect ratio combination, the experiments include nominal Reynolds numbers ranging from 15,000 to 45,000 in the first passage. A transient TLC technique is used to measure the detailed surface heat transfer coefficient distributions, and tomographic PIV measures the flow field characteristics. Enhanced heat transfer from the impinging flow on the side wall and downstream in the second pass is observed for all cases. Based on the first pass Nusselt number ratio, the accelerating case provides the best overall heat transfer enhancement. However, based on the second pass Nusselt number ratio, the decelerating case is a promising arrangement. If the Reynolds number is controlled, the constant cross-section case has the highest Nusselt number and heat transfer coefficient in the turn, and if the mass flow is controlled, the accelerating case exhibits the lowest overall average Nusselt numbers and heat transfer coefficients. The flow field results suggest the secondary flow induced by the turn is weakened when the flow accelerates after the turn. The opposite is observed for the decelerating channel. The strength of the counter-rotating vortex pair, turbulence level, and local heat transfer enhancements are closely correlated in a serpentine channel.
