Particle velocity measurement of binary mixtures in the riser of a circulating fluidized bed by the combined use of electrostatic sensing and high-speed imaging

The flow dynamics of binary particle mixtures in the fluidized bed needs to be monitored in order to optimize the related industrial processes.In this paper,electrostatic sensing and high-speed imaging are applied to measure the velocities of polyethylene and sand particles in the binary particle mixtures in fluidization.Experimental studies were conducted on a lab-scale cold circulating fluidized bed.Correlation function between electrostatic signals from upstream and downstream electrodes placed along the riser shows two peaks that represent transit times for the two types of particles.To verify the above results,high-speed imaging was adopted to capture the flow images of particle mixtures.Particle Image Velocimetry and Particle Tracking Velocimetry algorithms were utilized to process the resulted images in order to measure the velocities of polyethylene and sand particles.The reasons for two-peak correlation functions are illustrated based on the frequency spectrums of the mono-solid-phase electrostatic signals and the velocity difference between polyethylene and sand particles.Finally,comparisons on the velocities obtained from electrostatic sensing and high-speed imaging demonstrate the electrostatic sensor can roughly estimate the particle velocity of binary particle mixtures in the near wall region of the circulating fluidized bed.

Experimental and numerical investigations of cavitation evolution in a high-speed centrifugal pump with inducer

Along with the anti-cavitation performance,the high speed and the high power density,are the main trends in the development of centrifugal pumps.At present,the most effective method is to install an inducer in front of the impeller.However,the tip leakage of the inducer results in the vortex cavitation at the blade leading edge of the inducer,and the cavitating flow inside the inducer seriously interferes with the hydraulic behavior of the inducer as well as the impeller with the development of the cavitation,thus to badly affect the operational reliability of the high-speed centrifugal pump.In the present paper,the cavitating flow in a high-speed centrifugal pump with an inducer is investigated by numerical simulations and visual experiments for different cavitation numbers.A typical evolution process of the cavitation is shown,including the inception,the development and the deterioration.A general description of the pump head-drop phenomenon is made through the study of the local and global flow fields,and the relationship between the vapor distribution and the static pressure distribution along the inducer is determined to describe the evolution of the cavitation.This paper intends to provide the foundation for studying the overall cavitation state of a high-speed centrifugal pump,and designing the inducer with a better cavitation resistance.