PIV measurements of velocities and concentrations of wood fibres in pneumatic transport

A method for simultaneous measurement of the concentration and velocity of wood fibres suspended in air was developed. The velocity of the wood fibres was measured by the use of particle image velocimetry (PIV). The concentration of wood fibres was measured using the raw images from the PIV equipment as input data. An image processing procedure was used to determine the volume fraction of the fibre particles in the images. The method gave good qualitative and quantitative results for low volume fractions of fibres; for higher volume fractions the quantitative results were unsatisfactory.Latin letters C Concentration of fibres g/m³] - d Diameter of fibre m] - M_w Water mass kg] - M_f Fibre mass kg] - m Calibration mass flow kg/s] - m₂₅ Calibration mass flow at C=25 g/m³ kg/s] - n Fan rpm -] - t Thickness of light sheet m] - t Time between laser pulses s] - U_i Velocity component in i-direction m/s] - v Streamwise velocity m/s] - v_average Average streamwise velocity m/s] - x_i Particle displacement in i-direction m] Greek letters _f Volume fraction of fibres -] - _average Average volume fraction of fibres -] - Area fraction of fibres in image -] - Density of fibre particle kg/m³]