Air jet cooling of brake discs

Abstract

This paper reports on an investigation of a novel approach to the cooling of brake discs, based on the application of impinging air jets. This has the capacity to enhance the heat transfer coefficients at the disc surface quite considerably without affecting the disc design, so that the disc construction may then be optimized without reference to heat transfer. Using a purpose built test-rig, disc temperature histories were recorded using IR thermography for varying jet air flow rates, angle of impingement, dimensionless distance from the brake disc and rotational speed. As well as comparing cooling effectiveness for different test parameters, convective heat transfer coefficients were calculated from the transient temperature data and were used as boundary conditions for a finite element model of the process. The results obtained from this investigation suggest that the higher convection coefficients achieved with jet cooling will not only reduce the maximum temperature in the braking cycle but will reduce thermal gradients, since heat will be removed faster from hotter parts of the disc. Jet cooling should therefore be effective to reduce the risk of hot spot formation and associated disc distortion.