Session: 15-01: Internal Cooling Design Optimization

Paper Number: 152214

Heat Transfer Enhancement in Variable Aspect Ratio Serpentine Passages With Hemispherical Dimples 

The current study focuses on the effect of acceleration and deceleration in a two-pass channel with hemispherical dimples. Acceleration is produced by reducing the cross-section of the channel from 4:1 in the first pass to 2:1 in the second pass. To investigate the effect of deceleration, the cross-section increases from 2:1 to 4:1. The Reynolds number based on the smooth, rectangular channel in the first passage, ranges from 15,000 to 45,000. In the second passage, the Reynolds number ranges from 9,000 to 75,000. The staggered hemispherical dimples share a similar geometry to open literature, with a depth-to-imprint ratio of  δ/d=0.29 and a spacing of S x /d=S y /d=1.15 in streamwise and spanwise directions. The heat transfer characteristics are investigated by the transient, narrow-band thermochromic liquid crystal technique, and the flow field is recorded via tomographic PIV. The heat transfer results in the first passage for the accelerating flow are inline with literature values, with little change over the range of Reynolds numbers studied. For the accelerating channel, the combined effect of dimples and the turn produced higher heat transfer enhancement after the turn compared to a smooth counterpart. In the turn, the decelerating channel with dimples enjoys higher heat transfer enhancement than the accelerating one; while after the turn the heat transfer enhancement is even lower than that in its smooth counterpart. The time-averaged flow field measurement results show the flow has higher turbulence and vorticity after acceleration. With deceleration, the separation region is smaller compared with the smooth channel, but with weakened flow momentum, as the dimples divert the flow away from the divider wall. 

Presenting Author: Hanlin Wang Texas A&M University

Presenting Author Biography: Hanlin Wang is a Ph.D. candidate working at Turbine Heat Transfer Laboratory at Texas A&M University. His research primarily concerns the application of novel thermofluid measurement techniques, such as tomographic PIV, in the field of turbine heat transfer.

Authors:

Hanlin Wang Texas A&M University
Lesley Wright Texas A&M University