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Heat transfer question(in brake system)

  1. Mar 14, 2010 #1
    Anyone can tell me what is kinetics energy that needs to be convert into heat energy by the brake?( I mean can show me the formula or any journal)

    Anyone know any relevant heat transfer formula needs to be applied in order to determine appropriate sizes and surface area for the brake in order to achieve the cooling required?
  2. jcsd
  3. Mar 14, 2010 #2


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    The kinetic energy in the car = 1/2 mass * velocity ^2 = 1/2 m v2

    This gets turned into heat energy in the brakes and the brake disc heats up.
    The energy in the brakes = mass of brake disc * specific heat capacity * temperature difference = mcT
    You can use this to estimate what temperature the brakes reach.
    The disc then cools by transferring the heat into the air.

    The rate of cooling is proprtional to the area of the brake * the difference in temperature between the brake and the air.

    Getting actual values is very difficult since it depends on details of the air flow around the brake.
  4. Mar 17, 2010 #3
    Thanks for your reply. Can you give me more details about heat transfer formula needs to be applied to determine appropriate sizes and surface area for the brake to achieve the cooling required.
  5. Mar 18, 2010 #4


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    Homework? Your question is insufficiently defined. Once you define and parameterize the variables, the solution should be easier. Assume no air flow as your initial condition.
  6. Mar 18, 2010 #5
    Hmmm, i think i know what are you trying to tell me. I will try first before i asking next question. Actually it is a project. My title is about brake system. So, i need the formula for kinetic energy convert to heat energy.

    PS: Let say i have a sizes/surface area for the brake, can i calculate the heat?(assume the air temperature is 30)Need calculate the speed first?
  7. Mar 19, 2010 #6


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    Take a look in:

    Standard Handbook of Engineering Calculations by Tyler G. Hicks.

  8. Mar 22, 2010 #7

    I have car weight 3500 lb, rotor weight 200 lb, initial speed 50 mph, slowdown speed 0 mph
    calculate the average temperature?
    who know the formula?
  9. Mar 22, 2010 #8


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    Are you still trying to find the required surface area as in your original post?

  10. Mar 22, 2010 #9
    Yes, I am.
  11. Mar 25, 2010 #10

    Ranger Mike

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    holy cow..what kind of car you making that has 50 pound rotors per axle?
    way over board on unsprung weight..too much torque required to accelerate these...
    i hope this isn't a car designed for max fuel mileage cause it ain't gonna make it!
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