Cooling rate of a blade tip

[theonlydave]

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

 

[imok2]

Dave, I have no idea what you are talking about,but it got me interested so I thought this may be of some use to you

http://etd02.lnx390.lsu.edu/docs/available/etd-0530102-095332/unrestricted/Thesis.pdf

 

[ko99]

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 (

http://www.ecooling.biz)

 

[theonlydave]

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

 

[theonlydave]

the above link don't work well, the following link should work

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