Improving the Ventilation Efficiency of Jet Fans in Longitudinally Ventilated Rectangular Ducts

Abstract

The performance of a jet fan in a longitudinally ventilated tunnel is significantly reduced by the proximity of wall or ceiling where important shear stress losses occur. The paper focuses on the effect of jet fan inclination on the reduction of these losses; reducing losses means improved installation efficiency manifested by increased ventilation flow for the same fan power input. Experimental tests were carried out on a model at scale 1/5.5th. They allow one to determine the optimal jet pitch angle and the resulting benefit that could be drawn out of this solution in the case of tunnels with rectangular cross-sections. Also a few separation distances between the fan and the ceiling were investigated.