A case of drag reduction and pressure pulsations in pneumatic conveying

Experimental pressure drop results have been obtained for dilute phase pneumatic conveying of ordinary portland cement in a 100 mm diam. horizontal pipe with a test section length of 18 m.Significant drag reduction was detected in the presence of pressure pulsations introduced into the flow by a Roots type blower. Suppression of the pressure pulsations eliminated drag reduction.Compared with steady flow condition, it was found that pressure pulsations had a stabilising influence on the flow, permitting a 32% higher solids feed rate to be obtained before the formation of a stationary bed and the onset of unstable flow.Drag reduction in the test section was obtained at the expense of an increased pressure drop in the mixing and solids acceleration zones.