D�borah SITBON wrote: > > Hi, > I am designing a water current turbine (no head) expecting to > produce 150 watts on average. I am trying to choose a generator, but > for that i need to know the rpm range. > I don't how to calculate it. > The formula I found for common hydro doesn't suit with zero head. > And the method I found for wind power can't be useful because using > wind power efficiency graph. And this graph should be completly > different for water power. Isn't it? > > I hope you can help me. >
Debra, Once you know the relationship between the blade tip speed and water speed for the type of turbine you are interested in, then with a little geometry you can calculate the RPM for any water speed. I can offer you some help for three types of devices 1. FLOATING WATER WHEELS The freewheel blade tip speed is the water speed and it is well known that the peak power is obtained at half the freewheel speed. Hence, blade tip speed = water speed/2. 2. PROPELLOR TURBINES At www.ampair.com there are performance graphs for the Aquair UW turbine that allow the relationship between water speed and RPM for this turbine to be deduced. I have done the calculations - it turns out that over its useful range the turbine rotates at between 250RPM and 300RPM per metre/sec of water speed at peak power RPM. This corresponds to a blade tip speed to water speed ratio of between 4:1 and 5:1. 3. HELICAL TURBINES At the website for the Gorlov Helical Turbine [http://www.gcktechnology.com/GCK/pg2.html] it states that the turbine "rotates at twice the velocity of the water current flow". It's not clear what this means, but a likely interpretation is that at peak power RPM the tip speed to water speed ratio is 2:1. If these speeds are a little low for the generator you have in mind, then running the turbine at a little above peak power RPM is OK. Up to 20% above peak power RPM the output loss will only be a few percent. Regards, Max Enfield Planetary Power ------------------------ Yahoo! Groups Sponsor --------------------~--> Yahoo! Domains - Claim yours for only $14.70 http://us.click.yahoo.com/Z1wmxD/DREIAA/yQLSAA/FGYolB/TM --------------------------------------------------------------------~-> Does your company feature in the microhydro business directory at http://microhydropower.net/directory ? If not, please register free of charge and be exposed to the microhydro community world wide! NOTE: The advertisements in this email are added by Yahoogroups who provides us with free email group services. The microhydro-group does not endorse products or support the advertisements in any way. More information on micro hydropower at http://microhydropower.net To unsubscribe: send empty message to [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/microhydro/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
