Date: Wednesday 14th July 2021
Time and Venue: 03:00 PM @ A8-605 Meeting Room
Presenter: Mr. Michael Atkins, Lecturer
School of Mechanical and Aeronautical Engineering
University of the Witwatersrand, Johannesburg, South Africa
Bio-sketch:
Michael Atkins completed his MSc (with Distinction) in 2015 at the University of the Witwatersrand and is a PhD candidate at the same institution. In 2012 he won the Royal Aeronautical Society (UK) University Prize for the best graduating student of the University of the West of England, Bristol, UK. He has published 11 peer-reviewed journal articles, 3 book chapters and 8 conference papers. He is specialized in fundamental and applied aerodynamics, flow control, thermo-fluids in gas turbine engines, thermal - hydraulics in CANDU reactors, particle image velocimetry (PIV), planar laser visualization, and thermochromic liquid crystals (TLC's) transient heat transfer measurement techniques.
Abstract:
This presentation discusses insights into the internal thermal/fluidic behaviour of rotating ventilated brake discs. For the first time, the local internal temperature and convective heat transfer distributions within ventilated brake disc channels have been experimentally measured. The measurements are made within the rotating frame of reference using the thermochromic liquid crystal (TLC’s) heat transfer technique, and fluidic velocity field data was obtained using an adapted particle image velocimetry (PIV) method. The thermal/fluidic characteristics of different brake disc configurations (i.e., radial vane, curved-vane, pin-fin, and novel wire-woven bulk diamond (WBD) cored brake discs) were characterized.
For the radial vane configuration, the effect of the number of vanes on the internal thermal behaviour was investigated, providing insight into the radial, circumferential (vane-to-vane) and axial (inboard-to-outboard) convective heat transfer variations. In general, for a typical number of vanes used on automobiles (36-vanes), the overall thermal distributions are highly non-uniform, although uniformity improves as the number of vanes are increased. Significant thermal variation occurs between the inboard and outboard internal surfaces for all the brake disc configurations tested (18, 36 and 72-vanes), which possibly exacerbates thermal distortion (i.e., coning) of the brake disc when severe frictional heating occurs. For the maximum number of vanes, the end-wall thermal maps revealed distinct heat transfer behaviour attributed to the effects of enhanced secondary flow mixing that occurs above a critical rotational speed.
The investigation of the pin-finned internal thermal/fluidics shows that the bulk flow within the ventilated channel of a rotating disc follows a predominantly backward sweeping path between the pin-fin elements. The transient heat transfer measurements revealed that the internal local heat transfer distribution is highly non-uniform. Further detailed laboratory investigations using the TLC and PIV techniques and track testing of the novel WBD specimen compared with a pin-fin brake disc showed that the highly porous core achieves 21.3% increased heat dissipation. The mechanisms of the improving thermal dissipation are the substantially increased heat transfer surface area and greater utilization of the available end-wall and internal core surfaces for superior convective heat transfer.
