Conveying Air Velocity
Metin,
Argueably, it is more expedient to calculate conveying air velocity than it is to directly measure it.
Determine the air mass flow from the blower curve or from blower software. Mass flow divided by gas density (at that point in the system the velocity is desired) divided by the pipe cross section will give you the superficial gas velocity at that specific point.
Remember that the mass flow from the blower must be reduced by leakages that occur through the system, notably at the rotary valve(s) and at downstream diverter valves. Leakage data should be available from the manufacturers of these items.
Leakage of conveying air should not occur at ths pipe joints but, allowing for the type and condition of the joints, some leakage allowance may be in order.
Dennis Hauch ■
Solids Velocity
Dear Metin,
Solids velocity is always less than the gas velocity. Typically, it is about 20% less than the gas velocity, but the range is 0.5 to 0.95 x gas velocity depending upon the solids particle size and other factors. When going though a bend, solids velocity reduces from the inlet to the outlet of the bend. This reduction again depends upon solids particle size and other factors including the type of bend, but a typical number is 20%.
Gas velocity should be derived from the blower performance curves that you can get from the blower vendor. These curves give the gas flow at the blower inlet and this flow should be corrected for the actual ambient conditions at your site. This flow should be corrected for the blower slip. If you have a positive pressure system, reduce the blower discharge flow by the rotary valve leakage.
Regards,
A. T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting Services
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Conveying Velocity Determination
Prof Guner,
You could measure the velocity, and hence the volumetric flow rate of the air, at the end of the pipeline. This will automatically take into account the air leakage across the rotary valve. Then with the thermodynamic relationships p1V1/T1 = p2V2/T2 and pV = mRT you can evaluate the velocity of the conveying air at the start of the pipeline and anywhere else, provided that you can determine the pressure at that point.
For the material that you are conveying the particle velocity is likely to be about 70% of the air velocity, under steady flow conditions in horizontal pipeline, and lower when conveying vertically up. ■
Measurement Of Air Velocity
Prof Guner
If you really want to determine the conveying characteristics of different bulk materials, please consider not only to measure the air flow, but also to vary the airflow.
To know the minimum velocities as a funktion of product type and capacity you should be able to vary the terminal velocity f.e. between 15 and 30m/s ■
Measurement of air velocity
I have a positive pneumatic conveyor. I would like to determine the conveying characteristics of agricultural materials such as wheat, oat,soybean, lentil and corn. The pneumatic conveyor includes a roots blower, a rotary airlock feeder, a pressure separator. The problem is that where should I measure the air velocity. is the main entrance of air into blower suitable? or else on the pipe after the blower?
If you would help me about the measuremet of air velocity and material velocity? I would be very grateful to you.
Metin GUNER ■
Prof.Dr.Metin Guner University of Ankara Faculty of Agriculture Department of Agricultural Machinery 06110 Diskapi-Ankara-TURKEY guner@agri.ankara.edu.tr