because tip-of-vane air speed is the same as pressure (because you’re accelerating more molecules into tighter packing in a constricted cowling or valve). Forward-curved blades accelerate the air out (not just push, as with a backward-curved fan) and are leading candidates for pressure (despite the fact that they also produce higher volumes than the backward-curved configuration, in my experience). Tip speed of a radial fan is the most critical factor, with the shape of the blade coming secondary, perhaps followed by cowling design. I have experimented obsessively with what may be an optimal shape for the forward-curved blade – the involute of a circle, a spiral. I have built very efficient wind and water turbines from this shape. (see: http://www.fundamentalform.com/html/involute_wind_turbine.html )
I experimented with an involute spiral fan, using an old water turbine prototype, which was far from ideal. I too first mistakenly assumed that the backward-curved orientation of the vanes would give the greatest pressure. What a disappointment. But then I turned it around and discovered the superior attributes of the forward-curved orientation. It seems to roll the air out from centrifugal force overpowering the tangential pressure of the rotating vane, like a ball from a lacrosse or Jai alai racket. Because the involute curve is so smooth, it differentially moves the air throughout the entire surface of the “blades”, which can increase greatly without interference.
With a slow 1720rpm motor, only 3 vanes, greatly mismatched intake/outlet areas (outlet 3-times inlet area), it produced over 1.25” pressure, which I found very promising.
Unique Advantages of the involute spiral-bladed fan:
- The passageways between vanes is constant ~ not getting wider as you go out ~ no matter how many vanes.
- This allows numerous non-interfering vanes with a much larger surface area to grab the air and hurl it out in a smoothly accelerating laminar course.
- The vanes extend the entire area between inlet circle and outlet diameter, maximizing the space/pressure ratio.
- The curvature is maximum at the inner open circle, approaching radial. This hooked scoop configuration first gets the air spinning tangentially, shooting it out the ever-spiraling curved vane ducts, throwing it at maximum speed from the tips of the vanes.
- To get greater and greater pressure with less flow, Increase the degree of spiraling and number of vanes.
- The cowling on this prototype is also a segment of an involute -- further modification of this shape might improve performance.
Variables to test:
- increase the number of vanes (to say 11-15, keep odd) This will increase the blade surface area
- increase the length of the involute (to say 300 degrees) This will decrease the flow by making the inner circle smaller, and increase the pressure by providing more propelling force from longer blades at an angle more approaching tangent to the outer fan circle.
- match the intake hole areas (either from both sides or one) with equal output area
- Use a faster motor (3600rpm or more)
- Use a variable-speed fan to produce speed/pressure graphs for variations in blades, inlet, cowling, etc. ~ if we are pushing air against an ever-higher pressure, there will be a fall-off point, where air will find a lower pressure path to circulate back into the fan. Once we discover how these parameters work, perhaps we can improve the industry as well.
- I’ll bet we can get a simple fan to give 10” pressure or more.
This would make a great patent, but I haven’t time, $$$s or conviction to pursue such, so I’m sharing it in the Creative Commons domain. Use it, modify it, share it with others, as long as you credit me with the idea and involve me in the action, especially financially, since that seems to be the currently weak link in this collective abundance and prosperity. Nonetheless, all complex letters of law such as patents too often stifle innovation and the betterment of mankind, in the name of protection and security. We need to share more openly so all will benefit.
Toward this end I am licensing many of my discoveries, including this involute spiral fan, under the Creative Commons non-commercial category (http://creativecommons.org/ )
Share, Remix, Reuse — Legally, but involve me in commercialization.
Creative Commons is a nonprofit organization that increases sharing and improves collaboration. Wikipedia, Google and hundreds of millions of other users are creating a revolution of sharing through CC licensing. It is focused on Copyrights, not invention patents, so I welcome any other approaches others have with sharing while still benefiting economically.