max3.2

when it comes to inside cooling, its pretty much the same as outside. convection. vane design and other objects change velocity (some of the rotors look just like a cetr. pump) and create turbulence, thus increasing the HTC.

putting that into equations like mine (with h=const. or h=f(x,v,..) gets ugly. Thats a call for experiments and CFD...and even CFD will be a big problem. predicting changes from laminar to turbulent flow (as mentioned above) is still not working good.

I bet the FEA above used constant or simplified HTCs. In FEA, you will apply a so called boundary condition, specifying Heat loss/area, or in more sophisticated codes, a HTC and ref temperature. but they most certainly do not compute the exact HTC using a second CFD code..

I'll do my math this week and get some T(t) plots - lets see how that works with the rest of data...

alexjc4

You're right, in the FEA paper they use fixed htc:

h = 90 - 100 (W/m^2 K)

From "experimental determinations of the brake industry"

They get within 3% of empirical data for the system they are simulating though so its not too bad.

max3.2

well, using my eq. and plugging in 20m/s =approx 70km/h and a 300mm rotor, i get

approx 107 W/(m^2*K)

So not too bad. Ill do the solving the next days...

KaiB

I run Pagid RS29 (yellows) both front and rear. As I run a relatively strong rearward brake bias (compared to most), I wear front and rear at almost exactly the same rate.

Babalouie

I really shoulda studied harder at school...you guys lost me at page 2

max3.2

ok built a small model for car velocity.
implemented is constant accelration, constant braking pulses, wind resistance, mass reduction, brake force leverage.
i will then use velocity to compute htc and braking power. then plug it into T quation, voila, brake T(t). I attached acceleration (line: constant acceleration, curve:brakind and non linear wind force, both m/s^2) and velocity (kmh) profiles over 180s. maybe a bit harsh on the brakes...
by assuming 75% line pressure, 2piston caliper with guessed piston sizes im getting approx 0.85g decelaration...not to unrealistic.
also added a block model for convenience. maybe a bit hard to grasp but just a little bit education on mechanics :P
questions? ask! temperature calcs will follow after i loose my halloween hang over which i will get tomorrow







edit: again a cosmetic problem: last gain on the right is just 3.6 for km/h. the name with mass comes from c&p..

edit2: wind force changed so its there all the time. did NOT update images. new ones later

max3.2

there we go. still got to tune around. but all implemented, including radiation heat transfer. biggest piece still is convection
two spreadsheets, one for 300mm rotor, one for 420mm rotor.
please down be to hard on the actual values, as i said, first runs...I think seeing the brutal brakeabuse (look at veloity plots...but watch out, looong time), Ts are still too low
but you can already see: pad temp will pretty much rise constantly due to bad conductivity (no high t effects like radiation to caliper included for pad t...)
bigger rotor->Way better cooling

more to come. ask for specific input related data (pad sizes, rotor sizes, etc..)
code is matlab, so no c++ or general distribution, sorry for that.

http://www.file-upload.net/download-...2/BDT.rar.html

alexjc4

Just wow!

alexjc4

Max, you may have this info at your fingertips already but... if you want to tune/compare your data the FEA paper uses;
a four piston caliper
a 305mm rotor
160km/h to 0km/h stops of 0.6g
70% load on front brakes
vehicle mass of 1445kg
htc 90-100
rotor properties all as per cast iron.
discount heat transfer to pads and cylinders - which seems shaky.

They get an value by experiment of a peak 287 deg C from thermocouples in the rotor after the first stop. The FEA produces a cycling temperature of between ~160-270 deg C after the first stop.



@Steve and Grant - when you chaps got "fade" was it "hard pedal but reduced stopping power" or "pedal to the floor - oh cripes" type fade? One is the pads friction dropping off the other is boiling the fluid. The later is greatly effected by pad compound (how "metallic" and it is - as metalic pads conduct the heat much better to the fluid) and pad thickness (a half worn pad has way higher temps at the backplate and therefore through the pistons to the fluid).

Cheeksyboy

Ok, when I had fade with the WBC yellows at spa it was with a pedal that was a softening pedal that also needed to be pressed further to get any retardation. Out of experienced I released the brake and then reapplied. I only had it twice, same effect each time, given that I didn't get much runtime....for previously well documented reasons!

I've not had fade with the hawks but at oulton there was not the same need to she'd high speed within such short timeframes as at top of kemmel through to corner with no name.

alexjc4

That does sound more like the beginings of pad fade rather than fluid boil doesnt it. How much meat was there left on your yellows when they came out?

Looking at the pad friction and temp range data I got from vwvortex, the ebc yellow is 900 - 1100 deg f and the hawk blue is two steps up +1300 deg f and a bunch more friction. There is an intermediate step of Ferodo DS2500 or Mintex 1155, these are popular with the skybarge lot.

Cheeksyboy

Yes, defo pad fade and not fluid (I run blue so no boiling there). And I've had fluid heat fail before and that's much worse as you have no brakes!

Yellows have plenty of meat on them, back in for road use..... But as I said I didn't get much running so I'm not surprised. I suspect if I had been on track as much as the rest of you then I would have got through much of the pad material