Air or Gas laminar flow or leak testing principle:
There are many different methods to measure air flow.
The laminar flow method uses an element in which the air or gas flow measured becomes laminar.
Laminar flow is a fluid condition in which the flow is divided in "blades" (thin layers) that glide on one another,
with the layer in contact with the walls of the tube having zero velocity.
To make a flow laminar, the "Reynolds number" has to decrease which means in layman's terms that
you need to have the distance between the air and the walls of the tube reduced to a minimum.
Practically, you transform a large tube into a a number of small tubes and in those tubes
in the right pressure and flow conditions, the flow will be laminar.
The advantage of a laminar flow is that the pressure drop across this flow element is directly proportional to the flow.
So by measuring a tiny pressure drop with the right differential pressure sensor, we have an intrinsecally linear flow meter.
Of course, to make a real industrial laminar flow meter, that's not that easy.
of laminar flow test methods:
The larger the flow,the larger the laminar flow element has to be so it can become quite bulky.
The flow measuring element is a repeatable assembly of precisely machined parts so it is expensive to manufacture.
The measurement of air or gas flow is sensitive to temperature variations. Temperature affects the volume of air,
temperature affects the gas viscosity, and if you have a cheap sensor the reading of your sensor
The measurement creates a pressure drop so to be fast and accurate, you need to measure a very small differentail pressure.
Atmospheric pressure affects the readings since air is more or less dense.
So if your laminar flowmeter does not measure the test pressure, atmospheric pressure, gas temperature
and the very small differential pressure across the flow tube, in a very accurate way, you are in trouble.
A real industrial laminar flow meter takes at least those 4 measurements and processes them to give you a flow reading.
The differential pressure measured is very small so your differential sensor will break easily at the test pressure
unless of course it's an ATEQ patented differential pressure sensor that is designed to resist those conditions.
of laminar flow test methods:
The laminar flowmeter is by design linear, so one calibration
point is sufficient to recalibrate it properly.
The laminar flowmeter is extremely fast , if it measures small pressure drops, so there is no need to take a measurement
on a non fully stabilized signal or to re-calibrate after
setting the test timing.
The laminar flowmeter reading is greatly amplified in vacuum.
It is the preferred technology in vacuum air flow measurement
The laminar flowmeter is more resistant to contamination that heat exchange based flowmeters.
The laminar flowmeter is directionnal, it knows by principle which way the flow goes unlike heat exchange based flow measurement
No warm up time.
The effects of temperature on laminar flow are well documented in fluid mechanics books and can be adequately compensated,
so there is less drift with time of the measuring element.
There is no flow technology that is the best for every
test scenario. There is just a technology that matches better
than another your application and your budget.
Beware of companies who promote one technology as the latest
discovery universal leak or flow test solution, and claim they have
patented the wheel. That's just a clever marketing ploy.
The ATEQ applications engineer is there to listen to your
needs, and recommend the better matching solution accordingly.
Not a one shoe size fits everyone approach.
ATEQ uses 4 configurations for laminar flow leak testing .
They all have advantages and disadvantages depending on applications.