ON THE DIRECT AND RADIATED COMPONENTS OF THE COLLISIONAL PARTICLE PRESSURE IN LIQUID-SOLID FLOWS

In a recent study the collisional particle pressure was measured for l iquid fluidized beds and liquid-solid flows. The particle pressure was defined as the 'additional pressure' generated by the presence of the particulate-solid phase in a liquid-solid mixture. The particle press ure generated by collisions of particles was found to be composed of t wo main contributions: one from pressure pulses generated by direct co llisions of particles against the containing walls (direct component), and a second one from pressure pulses due to collisions between indiv idual particles that are transmitted through the liquid (radiated comp onent). This paper presents a summary of the technique to measure the particle pressure and the main results of that study. Additional exper iments were performed to further study each one of the components of t he particle pressure. The direct component was studied by impacting pa rticles on the active face of the pressure transducer. The magnitude o f the measured impulse was found to be related to the impact velocity, the mass and the size of the impacting particle. By comparing the mea surements with the predictions from Hertzian theory, a quantification of the interstitial fluid effects could be obtained. The radiated comp onent was investigated by generating binary collisions of particles in the vicinity of the transducer. The magnitude of the measured impulse was found to be a function of fluid density, particle size and impact velocity. Predictions based on impulse-pressure theory were obtained and compared with the experimental measurements. The model results sho wed goad agreement with the experimental measurements.