# Tesla turbine from old hard drives and minimal tools

11 Steps

## Step 8: Make disk spacers

There is a fair bit of interesting math and physics involved which determines how far the disks need to be spaced. Since we are just prototyping here, it is sufficient that the disks are spaced by 2 thicknesses of the average postcard (how scientific is this? Well, that's what the formulas indicate).

So, using the hole cutter, cut at least 12 washers with inner radius 15mm and outter radius of 20mm.
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gerrit_hoekstra (author) says: Jul 18, 2011. 6:41 AM
You won a medal for this? Well done! Your future as an engineer is secured!

I found a spreadsheet somewhere (and I don't know where it is now) that suggested that spacing should be about 0.8mm for something that has the viscosity of air. The more viscous the flowing material (water is more viscous than air) the bigger the spacing should be. It seems to not be too critical, but too tight and you loose energy from 'squeezing' your fluid through the gaps, and to loose and you loose energy from not sufficient fluid coming into 'contact' with the disk platters. My guess is that spacing is directly proportional to fluid viscosity (I do not know much about fluid mechanics).

The size of the inlet nozzle is of little importance - your aim is to get all the fluid to flow over the surfaces of all disk platters. I have a rectangular inlet that is a wide as the set if platters, which i made by simply sawing a cut into the one drive chassis, such that the airflow is directed along the outer tangent (i.e. 90degs to the radius line) of the platter. This way you will get maximum 'contact' between the energetic air and the platter surfaces.
Slicerr2 says: Jul 17, 2011. 5:39 PM
um i am doing a a science fair project this year with a friend and was wondering if you could give me the exact specifications to find out the spacing.

oh and by the way this years project is an extension of my project last year using your design it won me a bronze at nationals.
Slicerr2 in reply to Slicerr2Jul 17, 2011. 5:42 PM
oh and the sizing and angle calculations for the inlet nozzle would be great to