During frequent braking under race conditions the disk brake rotors on the car d

Question

During frequent braking under race conditions the disk brake rotors on the car described above reach a temperature of 500C. These disk brakes rely on forced convection to cool them. The dimensions of each disk rotor are: outer radius 130mm; inner radius 50mm; thickness 10mm. (Assume the disk is a simple donut shape ).

i) What is the surface area of the disk rotor (in m2)? (Include both sides and the edges)

ii) Given the heat transfer of the disk rotor is 120 W/m2/K, how much heat energy is radiatred from each of the disk rotors when the ambient air temperature is 30 C

Help with solutions and working out would be greatly appreciated

-----------------------

I posted this question before but the wrong answer was given.

Answers
i) 0.102m^2 ii) 5741W


I just wanted to know the working out that came to these answers

Explanation / Answer

there seems to be a slight error in the answers that you have given.
the procedure is given below.

(i) Area of disk = 2*(area of annular space)+(curved surface area of cylinder that results due to 10 mm thickness of the disk)

area of annular space = (1302-502)

total area of annular space = 2*(1302-502) = 90477.86842 mm2

area of curved surface = 2rh = 2*10*130 = 8168.140899 mm2

so

total area = 98646.01 mm2 = 0.09864601 m2

(the answer is close enough to 0.102 m2, i guess your answer has rounding off error, but the above procedure is the correct method to determine area)

(ii)

heat transfer = (co-eff of convection)*(total area)*(temp diff)

= (120)*(0.09864601)*(500-30) = 5563.635 W

the answers have 3.1% error which result due to rounding off at various places.

but the method is entirely correct.

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.