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low n' slow
17th Oct 2010, 21:03
Hi all!

I have a question that I thought I might be able to get a decent answer on from here.

What's the difference between convection cooling and impingement cooling in a turbine blade? I've been trying to figure it out from googling a little but I haven't found a good description yet. It's stated in the learning objectives for ATPL students but not covered in the Oxford material which I find a bit odd being a quite important part in keeping turbine temperatures down.

Could anyone on here explain these details to me please?

Regards/ LnS

rudderrudderrat
17th Oct 2010, 22:16
Hi LnS,

I thought impingement cooling is where the cooling air is directed squarely to the internal blade surface, convection cooling is where it's parallel with the blade surface.

Have a look at turbines here. (http://www.netl.doe.gov/technologies/coalpower/turbines/refshelf/handbook/4.2.2.2.pdf)

HazelNuts39
17th Oct 2010, 23:01
Hi LnS and rudderrudderrat;

I'm still amazed by the treasures available on the net if you know where to find them - many thanks rrrrt! The document describes impingement cooling and film cooling, but I couldn't find convection cooling. On another thread on PPRuNe, with some help of Wikipedia, I learned that 'convection' generally refers to a process of mixing. Maybe that helps.

regards,
HN39

1-26E
18th Oct 2010, 01:26
Do a Google search for <Convection cooling turbine blades> and then look at the Wikipedia article on cooling. Then look at almost any of the other references displayed for more technical information.

Impingement cooling is air directed onto the surface to be cooled striking or impinging upon it.

Film cooling directs a flow of cooling air along the surface to be cooled which acts as a protective boundary layer between the surface and the heat stream.

Convective cooling means that the air is made turbulent by various means and causes more heat transfer from metal to air.

low n' slow
18th Oct 2010, 13:54
Thanks all!

A very informative link rrrt! Excellent.

/LnS