for bhrescobar

For my own surprise, I've designed such a thing some time ago, but it was a pneumatic motor rotating a small shaft with a brake and with a flywheel attached to the last shaft.

Three questions have arisen with your picture:

1. Whats the size of your flywheel? (Inertia required, or, if already built, what's its dimensions and material - and weight).

2. What's the available size to fit things in, what's your desired total lenght for the assembly?

3. Please confirm requirement for absolute alignment of the generator. If you can offset it, you can use a chain, a pair of regular gear, a belt, some alternatives to change shaft speed. If not possible,You'll need a in-line reduction, can be a little more expensive. Please confirm.

Besides I feel honored to receive a post, let's allow the other guys give them oppinion too. I am really sure I'm not the best engineer or the most experienced one in the world, and someone always come here with a good idea.

Check it out. I'll help you with the design, it's really fun for me.

You mentioned in a side message that you'd like to dimension the flywheel against water hammering. I am assuming that you dont need to guarantee a certain speed range, your gen may be a DC or variable input speed type. In this case, the calculation would be different, and based on the effective power input distribution and allowable speed variation.

I'll post here a guide with very simplified equations so you can play with numbers by yourself. Please note that all values must be converted to SI before entering equations. Some are empirically determined, and are unit dependents. This is a collection of basic equations. I'd recommend you to consult a good fluid mechanics book or pipe design book to double check them and read some basic information so you can better understand it.

First of all, check your system and calculate water hammer according

ΔH=c·v / g (Allievi equation)

[piezometric heigh] = [celerity][speed of fluid] / [gravity]

c = 9900√(48,3 + k·D / e)

[celerity] = ... [k adim.] [Tube inner dia.] / [wall thickness]

k for steel pipe 0,5; for PVC 33,3;... check web for ref. values

Then you can calculate the stop time, i.e., the time taken for the flow under study to stop with the mentioned heigh of water hammer

ΔH= 2 L v / g t (Michaud equation)

L = tube lengh

If t equals to 2L / c, in a slow actuation, ΔH= cv/g

It also means that in a lengh L = ct/2 of pipe the values obtained with both eaquations are the same. From this point on, use use Michaud equation, and before it, use Allievi equation, to determine the maximum water hammer.

A simplified form to obtain the stop time is

t = C + (KLv)/(gHm)

K empirically determined

As well as "C"

Hm = manometric heigh = H static + cv/g

Then use equation

GD^2 = (8Q(Hm g t - L v)) / w^2 n

where

I = GD^2 / 4g

w = angular speed

n = machine efficiency

Then design your flywheel as light and cheap as possible using the inertia moment found. Try to do a design that has more mass in the outter diameter, of course. Choose to work with basics 1018 or 1020 steel strengh values.

Shaft dimensioning for the flywheel depends on the flywheel dimensions and weight.

It's pretty simple after the water hammer consideration. As your speed is not so high, you won't suffer with vibration effects that much.

Just remember to dimension the shaft for bending, for torsion, and add the stress. Assume some safety margin, let's say, 3 for fatigue effects, 2 for impacts in loads, a total of 6 safety factor would give you the ability to go to sleep in peace.

So you found the shaft diameter. Good. Go to bearing catalogs and find the right bearing for your application, based on speed and size. A small variation in shaft ends to fit bearings is allowable and desired (remember the safety margin?). Find also the recommended mount and lubrication method for the work you're imposing to the assembly.

Now, for the very same method, go and find the couplings, based on torque, speed and shaft dimensions.

I didn't have time to look for gearbox suppliers. Browse the web, find some suppliers with the numbers that you have now:

input: 1000 rpm, 382 Nm

output: 1500 rpm, 254.65 Nm

Nominal power 40 KW

In line, so, it will be a planetary gearbox, or something like this.

Contact some and ask if there's a product available off-the-shelf. If not, oh, ,...

They will tell you also what are the couplings required for the transmission.

After soing that all, go back to shaft design and modify it to fit the equipment you'll need to install. You'll note that everything will not be so dissimilar, because everything is made to fit nearly close applications.

I think you have enough to play with for now. Come up with some more issues when they arise (they will...)

And, in your place, I'd connect the turbine directly to generator, and install a relief valve in the pipe if water hammering is really a problem.

Oh, I forgot: wish you goodluck.