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.
