Velocity field and turbulence effects on heat transfer characteristics from surfaces with V-shaped ribs

The flow field of smooth surfaces and surfaces with V-shaped ribs (V-SR) was studied experimentally with a Laser-Doppler Anemometry (LDA) system. In addition, heat transfer characteristics were experimentally investigated. Heat transfer results from these surfaces under impingement of a circular jet array (5 x 3) using an infrared thermal imaging technique are presented. The velocity profiles were measured at Reynolds number of 10,000 and at H/d equal to 3 and 12. For each H/d position, profiles were collected from x/d = 0 to 6 axial locations. The heat transfer data were obtained at Reynolds numbers equal to 2000, 6000, and 10,000. Along the target plate, different boundary layer profiles were obtained for smooth and V-SR plates at Hid = 3 and 12. Positions of maximum radial and axial velocities and turbulence intensities have been determined for smooth and V-SR plates. For low jet-to-plate spacings, the production of turbulence kinetic energy is higher for the V-SR surfaces as compared to smooth surfaces. For Hid = 3, the radial velocities are higher for the V-SR surfaces as compared to smooth surfaces but for Hid = 12, the radial velocities are not nearly changed all x/d locations. The heat transfer results have also been compared with those of a smooth surface under the same flow conditions to determine the enhancement in the heat transfer coefficient from x/d = 0 to 3 locations. In these locations, the Nusselt numbers are higher for the V-SR surfaces as compared to smooth surfaces. The locations of the peaks and the minima are influenced by cross flow velocities which in turn depend on jet-to-plate spacing and V-SR arrangements. For all results, the Nusselt numbers at the stagnation points decrease with increase in H/d. (C) 2012 Elsevier Ltd. All rights reserved.