Heat transfer question(in brake system)

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Discussion Overview

The discussion revolves around the conversion of kinetic energy to heat energy in brake systems, focusing on the relevant formulas and calculations needed to determine the appropriate sizes and surface areas for brakes to achieve effective cooling. Participants explore theoretical and practical aspects of heat transfer in this context.

Discussion Character

  • Technical explanation
  • Homework-related
  • Debate/contested

Main Points Raised

  • Some participants provide the formula for kinetic energy as \( \frac{1}{2} m v^2 \) and discuss how this energy is converted into heat energy in the brakes, represented by the equation \( mcT \) for estimating temperature.
  • There is mention of the cooling rate being proportional to the brake area and the temperature difference between the brake and the air, though actual values are noted to be difficult to determine due to airflow complexities.
  • One participant requests more details on heat transfer formulas to determine brake sizes and surface areas for cooling, indicating a need for clarification on the initial conditions and parameters.
  • Another participant suggests that the question is insufficiently defined and emphasizes the importance of parameterizing variables for a clearer solution.
  • Several participants express urgency in calculating average temperatures based on specific vehicle weights and speeds, seeking formulas for these calculations.
  • A later reply humorously critiques the weight of the rotor mentioned, suggesting it may be impractical for a car designed for fuel efficiency.

Areas of Agreement / Disagreement

Participants generally agree on the basic principles of kinetic energy conversion to heat energy in brakes, but there is no consensus on the specific formulas or methods for calculating the required surface area and cooling effectiveness. The discussion remains unresolved with multiple competing views and requests for clarification.

Contextual Notes

Limitations include undefined variables and assumptions regarding airflow, which affect the calculations and estimations discussed. The need for parameterization is emphasized to facilitate clearer solutions.

apolo123
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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?
 
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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.
 
mgb_phys said:
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.

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.
 
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.
 
Chronos said:
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.

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?
 
apolo123 said:
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?

Take a look in:

Standard Handbook of Engineering Calculations by Tyler G. Hicks.

CS
 
urgent!

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?
 
apolo123 said:
urgent!

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?

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

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

CS

Yes, I am.
 
  • #10
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 going to make it!
 

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