GEK Fan Curve

[bear@apl]

A Fan Curve for the GEK V2.X Fan has been posted to the GEK wiki.

Purpose: This test was conducted in order to determine the flow produced by the fan provided in the GEK V2.X kits.

Results:
Below are the results from testing one fan/motor/housing combination. Maximum vacuum achieved was 3.5 inH2O. Maximum flow at 1 inH2O was approximately 25 m3/hr. Maximum power consumption was approximately 80 Watts (average: yellow - 35 W, red - 46 W, orange - 78 W).

Wiki: GEK Fan Curve

[DanielChisholm]

I uploaded an "improved" (hopefully) version of the spreadsheet, which includes calculation of discharge pressure losses (the pressure drop due to friction in the blue hose, plus its free-discharge loss), and a calculation of actual air power developed (in watts), which can be compared to the electrical power input to the motor.

I didn't plot any of my new data, but if anybody wants to add that, please feel free..

Bear, I'm glad you've taken a step like this to start to characterize the GEK's throughput. Let me take a quick stab at "baselining" the GEK's power level.

Let's say the fan is moving 15 m3/hour of ~100C gas. I'll SWAG that this gas has a density of ~0.8 kg/m3, so that is 12 kg/hour of woodgas. If we are running the GEK at an equivalence ratio of 0.25, that means that we are taking in 1.6kg of air for every 1kg of 0%mc wood that we consume. Let's add 0.15kg of water to that (about 13% mc). So for each 2.75kg of wet woodgas that we are drawing through the fan, we are consuming 1 kg of wood. So our 12kg/hr of woodgas means that we are consuming 4.36kg/hour (9.6 pounds per hour) of bone-dry wood, or 5.0kg/hour (11.0#/hr) of 13%mc wood.

At 8500 BTU/lb time 9.6# of bone-dry wood per hour, that is a thermal input of 81,600 BTU/hour, or about 24kW(thermal) fuel input rate. If we run an engine from this, at an overall 15% wood-to-shaftpower rate (20% engine efficiency, times a 75% cold gas efficiency), that's 3.6kW or 4.8hp of engine power.

If anybody would care to do some more work in establishing "Baseline Performance" for the GEK, it would be nice to start connecting various performance indicators. For instance, I am curious what the performance of the GEK's air preheating system is at this airflow level (or for that matter, at any identifiable airflow level). The one and only test I am aware of, Jim measured that the air was heated to 600C by the time it was ready for injection into the hearth area - but, I have no idea what sort of air and gas flowrate this occurred at. It could be that the GEK's air preheaters are grossly undersized, and only give these great levels of preheat when they run at trivial throughputs rates; or, they could be plenty big - but either way, I'd like to *know*....


FWIW, if this 15m3/hr of woodgas passes through a 3" diameter hearth, that is a superficial velocity of 0.92 m/s (expressed as 100C woodgas). The actual velocity of the gas, assuming it is at 800C and that the voidage in the hearth is 0.4, would be ((800+273)/(100+273) /0.4) = 7.2 times as much, or 6.6 m/s.

[DanielChisholm]

(I'm replying here to Bear's "6:54 pm on Mar 28, 2009" comment on the GEK wiki, since this is a much better place for back'n'forth...)

Hi Daniel, Jim,

Thanks for the calcs Daniel. It would be interesting to slowly work on thermal, fluid, and chemical modelling of the GEK. These kinds of calculations bring us closer...
Also, the new updated spreadsheet didn't seem to be updated, though I didn't compare closely. PBwiki may have some issues with files of the same name being re-uploaded.

As far as I can tell, the wiki _does_ allow multiple uploadings of the same filename - it keeps track of different versions of files. I just tried, and my "rev 2" is there. If you see column "N" in italics, titled "disch. Press", then you are looking at rev.2. If you only see the columns go up to "L", you are seeing rev.1.

The tube included the standard outlet. There was also an approx. 2 foot length of 2' pipe+orifice for the flowmeter in this case.
I could run some tests just on this length of tube/outlet at different air flows to get empirical information if needed.

I see you've added a very helpful second photo, which shows the iron pipe attached to the end of the blue hose. Is it half-inch pipe, or is it three quarters? Let me know and I'll update the spreadsheet and re-run the calcs. I would expect that it would create a much more substantial pressure drop, since it will produce a much higher speed jet (and all that pressure energy will simply be dumped, without any recovery, due to the free discharge).

I am not suggesting that you re-run the test (!), but, you should have connected the "free" end of your manometer to the discharge side of the fan (teeing it into the upstream side of the orifice flowmeter would be fine). This would then directly measure the pressure difference developed by the fan.

I'd like to look towards running tests on potential ejector designs for V3.X, but if there is a real need for other tests on the fan, I could run them.

Cheers,
Bear

I know that Jim is keen to get rid of the suction fan ASAP, so I guess we ought to work on getting a good successor solution there. However an ejector will require a blower or compressor of sorts to drive it, and we need to think about what we're going to use there, and get a good cheap GEKly solution established for it. As I see it, the advantage of an ejector is that it will allow us to use a conventional blower that only has to handle cold clean air, instead of hot tarry gas. I'll get back to that Real Soon Now...

[bear@apl]

I'm working on the affordable pumping/fan options. Stephen A. was using an Ametek blower from eBay, but retail prices on those are high. I need to order these to see how they work, but the Eco Plus X (1,3,5) commercial pumps look affordable and may have a reasonable output.

http://www.aquacave.com/eco-plus-5-c...lmin-1346.html

Duly noted regarding the measurement of the pressure developed by the fan. Although I was looking to easily get some ballpark flow rate people would get when running the fan under standard conditions without additional calcs. after the fact for outlet pressure drop. That info may be useful if people look towards other outlet connections though.

[jimmason]

yes, i think it is important that we come up with a characterization of the fan itself, separate of output pipe/nozzle, as other people will use this fan differently than we have. even we we it with different output options. the blue hose and 1/2" nipple is the usual way. but we also do it with a 1" direct into the swirl burner. that could also maintain 1.5" if we wanted.

the notion with this fan was to be able to cover most of the desired range of gas production needs of the standard gek. it was known not to cover all of them, as most of the larger ones will be pulled by an engine. it is designed so that these larger pulls can pass freely through the non-driven fan without restriction.

these larger flows would overwhelm the 1/2" nozzle anyways. so to see if we do in fact have a fan that flows as imagined originally, we should see what it can do sans output restriction.

while i think we will be going to an ejector soon, this fan will continue to be needed for various other projects, as well as used by others in their projects. and 70 people have it currently and would benefit by better characterization of it. it is not being abandoned. it is still useful time spent characterizing what it does.


jim