Jm. Beeckmans et al., EFFECT OF TAP SPACING ON OBSERVED DIFFERENTIAL PRESSURE-FLUCTUATIONS IN A PNEUMATIC TRANSPORT LINE, Canadian journal of chemical engineering, 74(6), 1996, pp. 834-839
The standard deviation of differential pressure fluctuations between p
ressure taps in a 31.7 mm i.d. vertical downer was found to be proport
ional to the square root of the distance between the taps when measure
d under otherwise constant conditions. This finding confirms the predi
ction of a theoretical model based on the Central Limit Theorem of sam
pling statistics. Although the paper only presents experimental confir
mation for downward flow, the theoretical model should be valid for fl
ows in all orientations. Except at very low solids flows, the pressure
gradient was found to be positive in the flow direction, indicating t
hat rise in pressure due to static pressure more than compensated for
frictional pressure losses.