| [GMCnet] John Biwersi's new direct replacement fan [message #269038] |
Tue, 06 January 2015 18:17  |
Advanced Concept Ener
Messages: 112
Registered: December 2014
Karma: 0
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Senior Member |
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I would like once and for all to put the idea of increased fan efficiency to bed. Lets assume that we want a 25% increase in air flow to make it worth while changing the fan. A 25% increase in air flow would, by the fan laws, increase the HP by 240% (1.25 cubed) Forget for a minute the fact that the pressure must also go up to move that air and HP increases by the square of the DP. That means that the efficiency of the fan must increase by 240% to break even on HP requirements. Only God knows how to increase the efficiency of a propeller fan blade by that much.
Now for Jim B question. You know me and my coach Jim and I would install the fan in a heart beat to decrease the noise which I firmly believe it does based on the feedback from this site. The fact that it decreases the moment arm on the water pump due to decreased weight is also a plus. But again I state that if you can control the speed of the fan to deliver just the right amount of air that keeps the oil cool while satisfying the water jacket temp requirements will deliver maximum efficiency and therefore minimum HP (fuel) requirements. If someone can get me the info on the electrically variable clutch that works on our units I will figure out the most simple control system , install it on my coach, test it and share the solution. The HP is to be saved by optimizing the quantity of air pumped across the radiator at any given load.
Jon Darcy
aces4nrg@gmail.com
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| Re: [GMCnet] John Biwersi's new direct replacement fan [message #269120 is a reply to message #269038] |
Wed, 07 January 2015 11:25  |
Jp Benson
Messages: 649
Registered: October 2011
Location: Fla
Karma: 2
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Jon,
Thanks for your thought provoking observations. According to my calculator, 1.25 cubed is 1.953. This would be a 95.3 % increase in horsepower not 240%. Nearly doubling the power requirements is still not very appealing. A more modest 10% increase in airflow would require 33% more horsepower. Conversely a more efficient fan would have a similar dramatic effect on reducing horsepower requirements. An increase in airflow should also produce a proportional reduction in duty cycle which must also be included in the calculations. The key to increased efficiency of any airfoil is reducing drag and I suspect the original fan blade could be significantly improved in this regard.
I think it's also fair to say that the assertion "more air flow for less power" is quite subjective. Even a small fraction of a percent improvement would render that assertion true.
I first became aware of the Biwersi fan in October 2014 when it was posted on the photosite and purchased one when I needed to remove my radiator for other reasons. My main concern was the potential fatigue failure of the 38 year old aluminum/steel riveted fan. Imbalance or damage would accelerate this type of failure. I've seen it happen more than once. The prospects of less noise and improved performance were appealing but secondary considerations for me.
One fact that I am aware of is that the Biwersi fan is not lighter but heavier than the original by 1 ounce. As for the moment of inertia, Mr. Biwersi has assured me that his fan has a lower moment of inertia but not knowing the mass distribution of either fan I am unable to verify. From observation I would state his assurance to be true but not by very much. Using just this fact alone one could modify the original fan and gain "more air flow for less power".
Modern CFD techniques not very practical in the 70's - have been used to dramatically improve the aerodynamic performance of all types of objects. Fan blades, essentially being rotating airfoils, are hardly the least among them. It's fairly easy to produce molded fan blades with aerodynamic characteristics far superior to the thin metal blades of the 70's style automotive fans. One good example of aerodynamic efficiency is the wing of a 747 which is reputed to have the same drag as a ΒΌ" wire flying under the same conditions. So they both require the same horsepower to move forward but only the wing would produce lift (i.e. move air). Judging from the noise of the original fan I wouldn't be surprised to find that it is operating in the stall region and thus would be very inefficient.
It would be nice to get hard numbers but we don't have them. From observing the fan design and the dramatic reduction in noise I tend to believe that the Biwersi fan in fact does in fact move air more efficiently.
I like the idea of an electrically activated clutch but would monitor oil, water and possibly trans fluid temps before designing an algorithm to activate that clutch. One concern would be reliability of a more complex system but then it seems that the thermally activated clutches also have a lot of reliability problems.
Regards,
JP
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