INJE UNIVERSITY

Inje University – Unsteady Milliscale Impingement Jets and Associated Vortices for Surface Heat Transfer Augmentation

This research activity, involving Dr. Ligrani, is in collaboration with Professor Dae Hee Lee, and associated graduate students, of the Department of Mechanical and Automotive Engineering of Inje University, located in South Korea. Of interest is jet impingement cooling of electronic chips, which are equipped with different cylindrical pedestal fin arrangements 1-2. More recently, confined, milliscale unsteady laminar impinging slot jets are investigated as they influence surface Nusselt numbers with constant surface heat flux and constant surface temperature thermal boundary conditions 3-5. Also considered are effects of confined impinging slot jets on heat transfer to concave and convex surfaces 6. The structure of the associated vortices, which form within the shear layers, which are adjacent to the slot jets, are investigated using flow visualizations 7. From these data, flow characteristics of confined, laminar milliscale slot jets are revealed, as the jets impinge upon a flat target plate, with a fully-developed velocity profile at the nozzle exit. The effects of Reynolds number and normalized nozzle-to-plate distance are considered for specific values of nozzle width. Transition from a stable symmetric jet to an unsteady oscillating jet is observed as the Reynolds number increases (with normalized nozzle-to-plate distance constant), where the Reynolds number associated with this transition decreases as the normalized nozzle-to-plate distance increases. Instantaneous visualizations also show unsteady lateral distortions of jet columns at experimental conditions corresponding to the presence of continuous sinusoidal oscillations, intermittent oscillating motion of the jet column, and jet flow fluctuation/flapping motion. Associated jet and vortex structural changes are determined for different modes of unsteadiness 7, including characterization of jet column unsteadiness using jet column oscillation frequency, and lateral and streamwise extents of jet distortion 7. More recent research considers surface roughness effects on impingement array cooling using different impingement hole shapes 8.

REFERENCES

1 Jet Impingement Cooling of Chips Equipped With Cylindrical Pedestal Profile Fins (Y. S. Chung, D. H. Lee, and P. M. Ligrani), ASME Transactions-Journal of Electronic Packaging, Vol. 127, No. 2, pp. 106-112, June 2005.

2 Jet Impingement Cooling of Chips Equipped With Multiple Cylindrical Pedestal Fins (D. H. Lee, Y. S. Chung, and P. M. Ligrani), ASME Transactions-Journal of Electronic Packaging, Vol. 129, No. 3, pp. 221-228, September 2007.

3 Confined, Milliscale Unsteady Laminar Impinging Slot Jets and Surface Nusselt Numbers (D. H. Lee, J. R. Bae, H. J. Park, J. S. Lee, and P. M. Ligrani), International Journal of Heat and Mass Transfer, Vol. 54, Nos. 11-12, pp. 2408-2418, May 2011.

4 Milliscale Confined Impinging Slot Jets: Laminar Heat Transfer Characteristics for an Isothermal Flat Plate (D. H. Lee, H. J. Park, and P. M. Ligrani), International Journal of Heat and Mass Transfer, Vol. 55, No. 9-10, pp. 2249-2260, April 2012.

5 Confined, Milliscale Unsteady Laminar Impinging Slot Jets: Effects of Slot Width on Surface Stagnation Point Nusselt Numbers (D. H. Lee, J. R. Bae, M. Ryu, and P. M. Ligrani), ASME Transactions – Journal of Electronic Packaging, Vol. 134, No. 4, pp. 041004-1 to 041004-11, December 2012.

6 Heat Transfer Measurements From Concave and Convex Surfaces With a Fully Developed Confined Impinging Slot Jet (S. J. Kim, Y. H. Kim, H. J. Park, D. H. Lee, and P. M. Ligrani), The 15th International Heat Transfer Conference, IHTC2014, Kyoto, Japan, August 10-15, 2014.

7 Visualization and Structure of Confined, Milliscale, Unsteady Impinging Slot Jets and Associated Vortices (D. H. Lee, H. J. Park, and P. M. Ligrani), Experiments in Fluids, Vol. 54:1420, pp. 1-15, 2013.

8 Effects of Hole Shape On Impingement Jet Array Heat Transfer With Target Surface Triangle Roughness (P. McInturff, M. Suzuki, P. M. Ligrani, C. Nakamata, and D. H. Lee), Paper Number GT2018-76228, ASME TURBO EXPO 2018: Turbomachinery Technical Conference and Exposition, Lillestrom, Oslo, Norway, June 11-15, 2018.

Copyright Trademarks Ligrani Research Group 2009