Well, it seems to work, but not quite as I expected.
I have built the U tube assembly. As such. it looks like one of those laboratory benchtop test stands.
When I applied the Oxy-Hydro to it, the water in the U tube moved as expected, and at a steady speed.
Oddly, when I measured the time taken to displace 20ml of water, it was almost exactly twice what I had anticipated.
When using the submerged bottle method, I displaced 20ml of water for every 1.8 seconds. The U tube system displayed a rate of 20ml per 3.6 seconds!
Now, I understand that the gas has to push the water up the column, but I would not have expected 25 grams of water to have such an effect.
Could it be that Hydrogen's tiny molecules compress more readily than those of ordinary air?
Hmmm, given this, perhaps I would need to calibrate this system in a different way.
Oh, but wait, there's more...
Suspecting that the steadily increasing weight of water was the culprit, I let the gas plant push 60ml of gas thru the U tube. Guess what, the time constant per unit of displacement was unchanged!!
Arrggghhh, confusion reins supreme!!!
Extreme drats. Back to the drawing board...
Another idea comes to mind now
Here goes:
If I had a small steel ball in a vertical glass tube, and induced the ball to oscillate vertically inside the tube, it's fall speed will be altered by the gas that is rising past it.
Theoretically, the ball would fall at a rate that is almost solely related to the effects of gravity - when there is no gas flow into the bottom of the glass tube.
When gas is allowed to flow, the rate at which the ball falls will decline.
The difference in speed would be a measure of the flow rate.
An electro-magnet would pull the ball up the tube - then release it.
A photosensor would detect when the ball has fallen a certain distance.
Timing would begin when the ball is released by the magnet, and would stop when the photosensor detects its presence at a pre-determined distance below the electro magnet.
At the same moment, the magnet would be turned back on. This would then make for a repeating cycle of vertical oscillation in the glass tube.
This system has the advantage of not needing a tapered tube. As long as the ball is a fairly snug fit inside the tube, it should work.
Does this sound like a workable solution?
Statistics: Posted by Steve-tee — Wed Dec 20, 2006 4:51 am
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Yes, the pressure issue is one concern that I should have mentioned.
Perhaps this is partially mitigated by the relatively small amount of water that needs to be displaced per measuring event?
Since the pressure curve is the same on each measurement cycle, maybe it could be accounted for by a minor calibration offset.
As water is quite a heavy liquid, perhaps something lighter will help.
I think oil is lighter, so this could be better.
On the subject of compression induced error, I suppose the degree of error can be reduced by having less gas space over the electrodes.
This would tend to increase the 'compression ratio', if that's the right term for it.
I better build a prototype, and give it a try on my 700mL per minute plant.
Maybe, it won't be quite so bad.
Fingers crossed
.Best wishes,
Steve.
Statistics: Posted by Steve-tee — Wed Dec 13, 2006 3:54 pm
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I have some doubts on your method of measuring gas output. Using U-tube method, output gas must have enough pressure to push water weight down the tube. Water weight increase when water level at the other side of tube goes higher. It might not be accurate to measure LPM but can be used to measure PSI.
The simple gas measurement using submerged bottle also varys depending on how deep we submerge the bottle. Correct me if I'm wrong.
Statistics: Posted by kumaran — Wed Dec 13, 2006 4:22 am
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Well, that might work. Hopefully, it will open in another browser window - for reference.
Here's the url again, just in case I messed it up:
http://www.geocities.com/amptramp2002/U_tubes.jpg
Hmmm, this computor stuff is a little confusing
Ok, assuming you have the intended image on your display, you'll see it has 5 stages to it.
Stage 1 is how it will be when initially filled with water = Equilibrium.
Stage 2 is the point at which the dump valve has closed after completion of the previous measurement cycle.
Stage 3 is when the timer is triggered by the rising water level.
Stage 4 is when the timer stops counting.
Stage 5 is when the water level rises to the trigger point for the dump valve.
Upon completing stage 5, the system reverts to stage 2. This process repeats for the duration of the intended run / measurement period.
Not shown, is the dump valve and gas inlet. For these images, it is assumed that these parts are placed at the top of the leftmost upright.
I hope to be building parts of this soon. Looks like I better take a look around the machine shop for all of the bits
.Best wishes, and accurately measured explosions
.Steve.
Statistics: Posted by Steve-tee — Wed Dec 13, 2006 1:57 am
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After spending a lot of time making a few experimental measuring devices, like submerged water wheels and funneled bubblers, I have come up with an idea that should perform as a very effective flow meter for gas.
It works on the displacement method which is normally used when we fill a submerged bottle with Oxy-Hydro.
Before this, I was trying to measure gas flow by letting the gas lift buckets on a submerged wheel, but this suffered from linearity errors and
bearing friction. On top of that, it was not going to be easy to calibrate.
I tried to use the bubbles themselves as elements of measurement. This turned out to be impractical also, as the bubbles would be of varying sizes.
Desperation was now setting in. I went and bought a thinking cap.
The pink ones seem to be best
.With my hair suitably restrained by said cap of thought, this concept arose......
We start with a 'U tube'. This has vertical sides, and a fairly gentle curve in the pipe that joins them.
If we put water in it, to a level that is about half way up the verticals, it will sit at the same level in both of those upright portions.
When gas is introduced into one of the uprights, it will impart downward movement to its water column.
Accordingly, the level in the other upright will rise by the same amount.
If left to run, the gas may push the water out of the other upright and begin bubbling through the 'U tube'.
This is fine, as this attribute serves as a standard bubbler for flashback prevention.
The rate at which the gas enters the U tube will be accurately reflected by the speed at which the water rises in its other side.
Given this, it is possible to use a pair of optical sensors to detect the position of the water in the column.
If the column holds 10mL of water per centimetre, and our plant produces 10mL per second, we'll see the water rising at a rate of 1 centimetre per second.
To stop the water from passing over the top of the column, we open the input side of the U tube to the atmosphere, by way of an electric dump
valve, just a moment after the level passes the topmost measuring point.
This dumps the Oxy-Hydro gas out into the airspace around the test gear, so no smoking, ok?
The valve stays open until the water level falls a little below the lowest measuring point.
Naturally, the water column is always operating above equilibrium to ensure that it can travel through the full working range under gravity.
Once the valve closes, the column again begins advancing at a speed that is determined by the gas production rate.
When the water column reaches the lowest measuring point, a timer starts. The timer continues to count until the column reaches the topmost measuring point, whereupon the timer stops and the column is discharged by the dump valve.
This process then becomes a self repeating cycle, whose speed is substantially influenced by the production rate of the gas plant.
Such a system, if there are no leaks, can readily measure production rates as low as 1 mL per minute.
Naturally, it can operate at appreciably greater rates also.
As the cycle is self supporting, there is no need for the operator to interact with it, other than to note the figure that appears on the timer.
This figure would be in seconds, or 10ths of a second - for greater accuracy.
I have yet to build this, as the concept occurred to me only last night. It appears to be very simple, yet should be accurate, easy to build, and very easy to calibrate. Further, it offers another less obvious function, that of leakage rate measurement.
While the system is at room temperature, and turned off, we'd raise the level in the measurement side of the 'U' by, say 50mL.
How do you raise the fluid level? Open the dump valve and blow air into the U tube, to impose an imbalance
.Perhaps this could be done by operating the gas plant for a few seconds.
If the fluid level begins to sink back towards equilibrium, a leak is apparent.
Given the time it takes, we can work out how bad the leak is - in specific units of measurement.
Is this useful? I don't really know, but it may help to resolve those annoying little leakage issues.
Talking of measurement, if we put a PIC chip into the equation, we can add the analog properties of Voltage and Current to the output figures.
The result would then be a regularly updating readout of Watt hours per litre.
Just imagine being able to get an extrapolated watt hours figure, just a few seconds after starting the system
.This idea needs to be tested and refined, but I think I am onto something here.
Well, here's hoping that this could be helpful.
Please do share your thoughts on this, as I am sure it could use a fair bit of refinement
.Best wishes to all,
Steve.
Statistics: Posted by Steve-tee — Wed Dec 13, 2006 1:38 am
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