Heat transfer air cooled solid rotor

[bennygod]

Hi all, long time listener, first time poster. It's been a while since my uni days of performign heat transfer calculations, so any guidance with a suitable method for the follwoing problem would be appreciated.

I have a solid rotor wrapped in a carbon sleeve. I know the k for both stator and sleeve (21 and 0.6 W/m.K). I also know the Q dumped from rotor into carbon = 500 W. The outside dia. of the sleeve is air cooled by air at 40C and ~70 m/s. Given that the air flow is turbulent and the Re (100000), Nu (200) and Pr are known, as is h (~200 W/m2.K).

I've got lots of info on composite hollow pipes where hot air/gas moves through the centre of the pipe and heat transfer takes place between pipe wall and then some extra lagging/insulation, but not sure how well this would translate for my needs?

My questions are:

Q1. How to calculate heat removed by air.
Q2. If the rotor was required to be kept at a certain temperature, can the air speed be determined?

Any help will be greatly received.

Cheers.

 

[IRstuff]

If you "know" that the heat dumped into the sleeve is 500W, then that power must leave the sleeve, no?

TTFN

FAQ731-376

 

[imcjoek]

Q1)
500W. Or temperature increases until 500W IS removed.

Q2)
A change in airflow changes Re, Nu, and h.
Finding a reliable h value is the heart of any convection problem.

My guess would be that you have a desired maximum (or operating) temperate and you must design your airflow (vent, fins, etc) in such a way to reach that temperature. If this is your problem, then you must research how to correlate "h" with your design parameters.

 

[vpl]

Q = [ṁ]c_p[Δ]T

Patricia Lougheed

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