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Cooling rate of a blade tip

Cooling rate of a blade tip

Cooling rate of a blade tip

(OP)
I have a specific problem about the cooling rate of a blade attached to a rotor spining at 20000rpm. The blade would achieve a temperature of 1200°C after heating and I need to find the cooling rate of the blade tip and its final temperature after a single quarter revolution. Since the blade would revolve at 20000rpm, a quarter revolution would take only 7.5 e-4 seconds. The blade tip speed would be 379.7 m/s. The radius of the rotor is 175mm and the blade  dimension is 15mm X 1.5mm with a height of 6.3mm in the direction of the rotor radius. There are 24 blades on the rotor so there will be 15° offset angle between the rotors at the rotor centre. I done a theoretical modeling of the problem, predicting turbulent wake at the blade tip. Does anyone have any idea how to compute the convective heat transfer coefficient? Can I use the equation for a transient heat conduction of a semi infinite body with a surface convection boundary here?

Dave

RE: Cooling rate of a blade tip

I'm not sure I understand the question.  

If it's a steady state problem and you want to find the convection coefficient, there are ways to estimate it but a specialized software simulation may be required for an accurate value.

If it's a transient problem (blade at 1200C in steady state, then the heat is turned off) blade mass & specific heat & ambient temp are required.  But I'd be very surprised if the blade temperature changed by a measureable amount after a quarter rev!

ko  (www.ecooling.biz)

RE: Cooling rate of a blade tip

(OP)
Thanks imok2 for the file, I have a similar doctorate dissertation but I thought if anyone has any correlation equation for rotating machines that I can apply quickly. I got some diagrams to clarify the poblem. It is at the below link.

 http://home.pacific.net.sg/~emailcs/heat transfer question.pdf

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