wheel hubs and rotate with the wheels. When the brakes are applied, pads are pushed against the faces of the disc causing frictional heating. The energy is transferred to the disc and wheel hub through heat conduction raising its temperature. It is then heat transfer through conduction and radiation to the surroundings which prevents the disc (and pads) from overheating. If the combined rate of heat transfer is too low, the temperature of the disc and working pads will exceed working limits and brake fade or failure can occur. A car weighing 1200 kg has four disc brakes. The car travels at 100 km/h and is braked to rest in a period of 10 seconds. The dissipation of the kinetic energy can be assumed constant during the braking period. Approximately 80% of the heat transfer from the disc occurs by convection and radiation. If the surface area of each disc is 0.4 m2 and the combined convective and radiative heat transfer coefficient is 8
Disc brakes are used on vehicles of various types (cars, trucks, motorcycles). The discs are
mounted on wheel hubs and rotate with the wheels. When the brakes are applied, pads are
pushed against the faces of the disc causing frictional heating. The energy is transferred to
the disc and wheel hub through heat conduction raising its temperature. It is then heat
transfer through conduction and radiation to the surroundings which prevents the disc (and
pads) from overheating. If the combined rate of heat transfer is too low, the temperature of
the disc and working pads will exceed working limits and brake fade or failure can occur.
A car weighing 1200 kg has four disc brakes. The car travels at 100 km/h and is braked to
rest in a period of 10 seconds. The dissipation of the kinetic energy can be assumed constant
during the braking period. Approximately 80% of the heat transfer from the disc occurs by
convection and radiation. If the surface area of each disc is 0.4 m2 and the combined
convective and radiative heat transfer coefficient is 80 W/m2 K with ambient air conditions
at 30oC. Estimate the maximum disc temperature.
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