Air Speed Sensor
Dear Hartono,
You can use the propeller anemometer or a heated wire anemometer if you can run the system without material. If this is not possible, use a pitot and differential pressure gauge to measure velocity pressure, from which you can calculate velocity. The standard pitot is accurate in this velocity range but is subject to blockage because of small orifices so you have to do the measurement quickly.
An S type or "special" pitot is less sensitive to blockage but needs to be calibrated against a standard pitot in clean air to establish a correction factor. Again, you have to do the measurement quickly if there is a lot of material in the airflow.
If you use one of the direct reading electronic pressure gauges which reads in metres/second, the answer comes in a few seconds.
Michael Reid. ■
Re: Air Speed Sensor In Pneumatic Separation Column
Thanks Reid.
I would like to make it an automatic continuous system whereby the sensor system would maintain a windspeed of about 10 metres / sec - regardless of amount of load passing through - inside in the vertical column by controlling the damper.
That is my problem. How to have a digital sensor that takes continuous reading with material passing through in the column.
I thought of using a membrane or diaphgram replacing part of the column wall - no blockage, no jam, little impact on sensitive part. The flex of diaphragm would indicate the pressure. But Google doesnt seem to indicate this kind of sensor exist.
Any ideas?
The peak load is about 15 tonnes / hour and average is about 10 tonnes / hours. The material consist of 65 % fibre (unwanted) and 35% nut (wanted).
Regards
Hartono ■
Separation Control Scheme
Using a direct velocity measurement for damper control may not be the best solution.
Two reasons for this 1) the velocity measurement element must function reliably with material present in the air stream and 2) signal conditioning aside, the measured velocity will vary all over the map which means the damper must constantly hunt and seek.
A better solution. Consider controlling the damper based on an air mass flow signal. By measuring differential (velocity) pressure, static pressure and temperature the air mass flow can be calculated and the resulting signal fed to the damper.
The advantages of an air mass flow control include a non-invasive / reliable signal measurement, a more stable control signal to the damper, and unit ratio value that would be useful on the process flowsheets.
My thoughts.
Dennis Hauch, PE ■
Air speed sensor in pneumatic separation column
I would like to measure the wind speed of a pneumatic separation column so that losses would be lesser.
the terminal separation of nut (heavy) and fibre (light) is around 9-12 metres/second. Too high a speed would result in nuts being lifted up and being lost. Too low a speed would result in fibre clogging up the downstream process.
I control the air speed by widening or narrowing the damper, not the fan motor itself.
I cannot use the classical propeller anemometer or hot probe anemometer since the sensor will be impacted with fibers and nuts
An indirect way of measuring is using a manometer, find the differential in pressure and the speed of air is known.
any other ideas how to measure air speed in a pneumatic separating column?
thanks
hartono ■