ISSN Online: 2377-424X
International Heat Transfer Conference 12
Heat transfer from a dimpled surface with and without free stream turbulence in a thermally developing flow
Abstract
The objective of this study was to characterize the area averaged heat transfer performance of a dimpled
surface in a thermally developing flow with and without free stream turbulence. Two 30 by 30 cm plates, one
smooth, one dimpled were constructed and tested in a wind tunnel. The dimples are 3 mm deep with print
diameters of 16 mm and are configured in a staggered array of 15 rows and 13 columns. Tests were conducted at
channel heights from 1.27 to 3.81 cm and Reynolds numbers (based on hydraulic diameter) from 20,000 to
60,000. The smooth plate results were compared to the Dittus-Boelter equation for turbulent flow in a pipe and
found to agree within 5% while the dimpled plate data showed a 30-40% increase in the average heat transfer
coefficient. Two different metal mesh grids were placed upstream of the test plate to induce 3-4% and 6-8%
turbulence levels in the channel. We found that although the heat transfer coefficients on both the smooth and
dimpled plates increased when turbulence was induced in the channel, the overall benefit of the dimpled surface
decreased.