The existing turbine has a rotor diameter of 300mm for a speed approx. 800 rpm, H=4m and Flow=150-180 l/s. Which should produce about 4kW-5kW, without generator and mechanical efficiency included. If you increase the operating speed for the same site conditions, the diameter needed decreases and the blade angles need to be recalculated. A similar powered turbine with a lower head of say H=2m but with a larger flow rate of 340 l/s would require a larger diameter runner and a slower operating speed (maybe 400-500rpm). In this case, the diameter could be as high as 500mm depending on what specific speed you choose. So I suppose, propeller diameter anywhere up to 500mm might be of potential use if they match the blade angles needed for a specific set of turbine operating conditions.
The main constraint with regard to developing countries is that the method of manufacture is cost-effective for local manufacturers and the equipment and materials are readily available. For example, the manufacturer we are working with in Peru only has basic equipment such as sheet metal bender, welder and a method to heat the metal for shaping. No casting or milling processes are required. Another low-cost option might be to use a suitable boat propeller but as was outlined in the previous post by Eilrem it can be difficult to source a specific prop that suits the diameter and blade angles that you require for the site conditions. It is an iterative process to a certain extent so if a suitable prop is sourced then the speed of the turbine can be adjusted to suit within limits. regards Robert -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] Behalf Of Girish Kharel Sent: 04 September 2005 22:05 To: [email protected]; Simpson, Robert Subject: Re: [microhydro] boat propellers as runners This sounds like an interesting project. For a range of head (say up to 10m) and flow conditions in the 0-5 kW power range, what would be the corresponding speed and rotor diameter? This would then give an indication of the sizes of propellers that we are interested in. I am assuming that you have already done the theoretical work on the application range. You mention that the design is for use in developing countries. What particular conditions/constraints do you have in mind? Regards Girish ----- Original Message ----- From: "Simpson, Robert" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, September 06, 2005 2:47 PM Subject: RE: [microhydro] boat propellers as runners > Do you have any more details about schemes where a boat propeller was used or modified for use for a low-head turbine? > > I am currently working on a project to develop a design method for cost-effective manufacture of propeller turbines in the pico-hydropower range (ie 0-5kW). The focus so far on the method of manufacture for the runner has been to cut the blade shape from flat sheet steel and then bend and twist into the desired geometry using some heat and hammer. From computer simulations conducted so far it doesn't appear that much efficiency is lost by using constant thickness blades as opposed to profiled blades, as long as the pitch angles and twist are designed correctly for the site conditions (head, flow rate, operating speed). These will hopefully be confirmed soon with field testing of a prototype turbine. > > The overall aim of the project is to develop a design manual and software that can be used for the design of low-head propeller turbines for use in developing countries. Any other comments, advice or potential case studies etc.... would be most welcome. > > Robert Simpson > > > > -----Original Message----- > From: [email protected] [mailto:[EMAIL PROTECTED] > Behalf Of [EMAIL PROTECTED] > Sent: 05 September 2005 22:12 > To: [email protected] > Subject: Re: [microhydro] boat propellers as runners > > > Boat propellors definately do work in micro hydro. If you machine the > rounded tips off a bit , they are even better. Add some pre swirl vanes, or a > scroll case and you have a low cost approach > > > [Non-text portions of this message have been removed] > > > > > > > > Does your company feature in the microhydro business directory at http://microhydropower.net/directory ? 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