Yeditepe University, Department of Mechanical Engineering June 2nd, 2023
Spring 2023 Semester, ME212, Thermodynamics II
Midterm Exam; Question 1 (25 points)
Duration: 20 minutes + 5 minutes for uploading your answer to the YULEARN = 25 minutes
Automotive manufacturers are looking for ways to improve the cars' overall efficiency, and one
way they are interested in is the brake system of the cars for improvement. In this problem, let us
look into a disk brake system of a car. Typically, a disk brake system consists of a disk brake and
brake pads. We want to analyze this problem from the first and the second law of thermodynamics
perspective; therefore, let us assume that one of the car's disk brake system is 3 kg in mass and
brake pads are 1.5 kg in mass. When a driver needs to stop, he/she presses on the brake pedal, and
the brake system stops the car by applying friction force to the wheels. Note that there is a heat
dissipation during stopping. Temperature measurements show that disk brake surfaces reach up to
2XYC just after the brake is applied. The driver parks his/her car and stops the engine by letting
the brake system cool down to a surrounding temperature of 20C. Determine the exergy
destruction for the braking process by considering the braking and brake system to be cooled to
the surrounding temperature. Specific heat of the brake pads can be taken as 0.5 kJ/kg-K.
Reference temperature for this problem is surrounding temperature.
Note that the XY value in the temperatures is the last two digits of your student ID number. In
other words, if your student id ends with 45, then you should take the temperatures as 245 C.
Also, note that you may not get any point from this problem if you solve this problem with different
numbers than given in the problem statement.
