An investigation of local heat transfer characteristics in a ventilated disc brake with helically fluted surfaces

Abstract

Local Nusselt numbers in the cooling flow passage of the automobile disc brake with helically fluted surfaces are presented. The flat surface in the flow passage is modified to the helically fluted surface for the purpose of enhancing the heat transfer rate, thereby reducing the thermal stress and deformation in the disc brake. Thermochromic liquid crystals and shroud-transient technique are used to measure spatially-resolved surface temperature distributions, which are used to deduce local Nusselt numbers. The Reynolds number Re ranges from 30,000 to 70,000, the helix angle θ is fixed at 45° and the dimensionless streamwise distance z/d ranges from 1.5 to 4.5. The results show that in general, local Nusselt numbers monotonically decrease with a distance away from both windward and leeward crests of the helical flute and reach a minimum value near its valley for all Re’s and z/d’s tested. The local Nusselt numbers on the helically fluted grooves are maximum 51.6 to 93.7% higher than values measured on the flat surface. The heat transfer enhancement magnitudes become more pronounced with smaller Re and z/d. The largest enhancement occurs at the windward side of the helical flute at z/d=1.5 and Re=30,000. It is also found that at Re=30,000 the average Nusselt numbers on the helically fluted surface are maximum 37% higher than those on the flat surface. The numerical results show that with 10 braking cycles, the temperatures with helically fluted surface are maximum 44.3%, 36.8%, and 36.6% lower than those with the flat surface in the inlet, the center, and the outlet, respectively.