Prediction of Airflow With Swirl in Perforated Polyethylene Tubes

Abstract

The influence upon flow of fan induced inlet swirl is examined for two commonly used sizes of uniformly perforated polyethylene ventilation tubes (polytubes). Swirl is present at the inlet of most polytubes that are directly connected to a supply fan whether or not an antiswirl device is used. Four experimentally obtained inlet swirl angles are examined using swirl modified pressure recovery coefficients, pipe friction factors, and orifice discharge equations. A computational procedure divides the polytube into five equal length segments to obtain a rapid yet acceptably accurate procedure. An iterative microcomputer spreadsheet solves the resulting set of simultaneous equations, providing pressure and flow discharge profiles along the tube that are in very good agreement with the experimental data and with the data of others. An extension of the analysis for uniformly spaced orifices indicates that supply swirl angles greater than 25 deg and large length to diameter ratios should be avoided.