Hi everyone !
I'd like to realize a fluidization which consists in making a gas go through a bed of powder so that the friction due to the velocity of the gas U can lift of the layer of powder. It brings some great mechanical properties such as good thermic exchanges and good mass repartitions.
To do so, I have to find the minimum fluidization velocity with pressure sensors (or with a flowmeter but it's much more complicated to acquire the data with it) to see the loss of charge through the bed.
I don't know what pressure sensor (differential or not ? barometer ?) i should use.
The pressure measured has a value close to several bars.
This sounds like an industrial process. I have had excellent results with the Omega PX309 series of pressure sensors, with 0-5V outputs. They are expensive, but extremely high quality and rugged, so will last for years. http://www.omega.com/pptst/px309.html
Thank you, this seems to be what I have been looking for.
Since the distance between the two pressure measure points, I will have to link the sensor to the system with two pipes.
Don't to think it will alter the values of the pressure ?
I don't know what pressure sensor (differential or not ? barometer ?) i should use.
The pressure measured has a value close to several bars.
A differential pressure sensor is the proper sensor to use for this measurement. Just select a PD sensor that covers the maximum pressure difference it could see, worst case would be a totally plugged bed. As long as the medium is air and it's temperature doesn't exceed the sensor's ratings then even the inexpensive plastic differential pressure sensors should work OK.
mytebello:
Thank you, this seems to be what I have been looking for.
Since the distance between the two pressure measure points, I will have to link the sensor to the system with two pipes.
Don't to think it will alter the values of the pressure ?
Not if there is no condensation allowed to build up in the two sensor leads (pipes). One trick is to mount the sensor above the highest measurement tap and run the connecting leads down, thus allowing for 'self draining' of any condensation in the two measurement leads. Trapped condensation will effect accuracy of measurements.
Your diagram suggests that the apparatus is open to the atmosphere at the top. Is that the case?
If so, why do you need a second pressure measurement, since the pressure there will be atmospheric pressure?
There are two types of pressure gauge, absolute (i.e. relative to the vacuum) and relative (to atmospheric pressure). For pressures of several bar, most are relative.
The problem is that if the top is closed as the gas is coming, the pressure at the top won't stop raising. But if it is open, it is obviously the atmospheric pressure...
I don't know how to measure the loss of pressure through the bed then...
I can use a flowmeter too to get the velocity U but it's a bit harder to install properly.
I don't understand your response. Is the top open to the atmosphere, or not?
If the top is open to the atmosphere, then any "gauge" type pressure sensor will give the the pressure relative to atmospheric pressure. This is what you want -- it measures the pressure difference between the lower and upper chambers.
In contrast, an "absolute" pressure sensor will measure the pressure relative to the vacuum. If you use the absolute type, you would need two sensors, one for the top and one for the bottom.
mytebello:
well in fact, the ascending gas has a velocity so the pressure won't be equal to the atmospheric pressure (venturi effect)
this actually depends alot on the 'surface area' of the gas inlet and outlets, among other things. I am almost positive the OP can ignore any venturi effect here.
My 2 cents: If the top is left open, which it should be, a single pressure sensor can be installed at the bottom of the bed, but i really doubt that you will get a usable reading there. Can you measure the pressure of the gas before it gets to the powder bed?
without a 'top' you wont get a "pressure" reading like you expect. depending on your powder medium... you might not even be getting 1 psi of "pressure" in the bed.
PSI(my favorite pressure unit) is pounds per square inch. on a 10 square inch bed, at 10psi the powder will be pushed up with a constant 100lbs(!) of force over the entire bed. (assuming a perfect airflow) this would probably throw powder everywhere. This is why i think you should measure the pressure BEFORE the input.
Yes you are right but the loss of pressure through the bed has to be constant after we have reached the fluidisation.
Edit : U here is the velocity of the gaz : (U = Q/S)
It means that the pressure measured before the powder medium stays constant when we reach a certain velocity for the gaz.
It seems a bit odd.
That's why i wanted to acquire the pressure before and after the bed even if the second one seems obviously to be of atmospheric values
Do you think that the difference of pressure is too tiny ?
