
#1
Jan913, 09:58 PM

P: 6

How do I convert the RPMs of a simple turbine (e. g. a windmill) into the power it generates? Let's say that I want to know if a single windmill of a certain size can power a refrigerator. Assume that I already know how long the blades have to be to produce the RPMs, and I know the energy requirements of the refrigerator. I am only looking for a basic equation of RPMs to power (watts or joules). Thank you.




#2
Jan1013, 01:30 AM

P: 669

I don't know the answer, but I at least know that its not that simple.
RPM alone don't tell the full story. You could get a small babytoy scale turbine to rotate at the same RPM as a big power turbine. What you can get is  for a given wind speed, and for a given turbine type of certain size you can find out the mechanical power output. The mechanical to electrical conversion is often >90% efficient. The theoretical limit to the maximum power that can be harnessed is given by Power_max = 0.5 x Swept Area x Air Density x Win_Velocity^3 But to get anywhere near the maximum power you need to have a stateofthe art turbine design. 



#3
Jan1013, 01:54 AM

P: 6

Hi, I_am_learning  Thanks for your input. I was afraid it might not be as simple as I had hoped. Apparently I will have to keep digging.




#4
Jan1013, 05:26 AM

Mentor
P: 22,001

Power output of a simple generator
Power is rpm times torque divided by 5252 (English units). http://www.largiader.com/articles/torque.html




#5
Jan1013, 09:32 AM

P: 6

Thanks, Russ!




#6
Jan1013, 12:55 PM

Sci Advisor
P: 3,139

i've been looking for an easy to remember number for that conversion, and 5252 is it . 52 twice makes me think of Tex Ritter's "Deck of Cards" So at 5252 RPM torque and horsepower have the same number. That's right in operating band of small outboard motors i tinker with. old jim 


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