Investigations of Single Jet Impinging on Plates With Circular Dimples

In this paper, experimental and numerical investigations are both conducted to study the effect of circular dimples on the heat transfer performance of jets impingement. The circular dimples, set as one kind of surface structures on flat plate, have the same diameter of 3 mm but with different depths: 1.2 mm, 0.9 mm and 0.6 mm. Furthermore, in order to understand the mechanism of impingement heat transfer with circular dimples deeply, three different jet locations are studied in this paper. For the experimental investigations, the infrared thermography is applied to gain the temperature distributions on the flat plate. A comparison is made between the numerical results and experimental data, which indicates that they are in good agreement. The numerical results show that the dimples on the plates have significant effects on the impingement heat transfer. The overall averaged and local heat transfer coefficient in a single jet impingement on the smooth and dimpled plates are obtained and compared, as well as the flow structure. The effect of the dimples on the heat transfer performance of the target plates is different for different locations of dimples. Velocity distributions and streamlines near the target plates are also shown to explain the heat transfer characteristics. From the investigations, for the dimpled plates with different depths, the deeper dimples have the better averaged heat transfer on the target plates. The dimpled surface enhances the heat transfer performance obviously with H/D of 1.5. However, with the distance between the impinging hole and the target plate increasing, the transition location of the impact zone and the wall jet zone advances and the enhancement effect decreases. Moreover, further downstream region on the dimpled plates shows lower heat transfer enhancement effect and the effect becomes approximately invisible after X/D is larger than 3. The fluid in the dimples with different depths has the same streamline. The heat transfer enhancement at the downstream of dimples is better than the upstream.