Pressure losses in pneumatic transport

A model is derived to calculate the pressure losses originating from the dilute phase pneumatic transport of coarse particles in the horizontal stationary flow regime. The model is based on the balance of drag forces and frictional forces acting on the particles during pneumatic transport. The particles are characterized by the particle terminal velocity, the particle âwall sliding friction coefficient and the coefficient of restitution between particles and wall. The influence of the inhomogeneous particle distribution in the pipe is taken into account using a particle density distribution resembling the barometric height formula. The model is verified experimentally by the use of particle velocity measurements and particle-wall collision measurements during pneumatic transport. For this purpose measuring techniques and tools have been developed. A Froude number, based on the mean square value of the radial particle-velocity component, appears in the model as an empirical parameter. This Froude number increases with increasing average air velocity but may also depend on the pipe diameter and the solids-mass flow to some extent. However this dependency could not be quantified and may restrict the accuracy of pressure loss predictions with the model. The assumption of a linear relationship between the Froude number and the average air velocity provides scaling and prediction possibilities for pressure losses.