Radial distribution characteristics of droplet size and velocity in annular mist flow around the bluff body

Abstract

Wet gas is a common gas–liquid flow type in chemical processing. When measuring the gas flow rate and liquid load of wet gas with a vortex flowmeter, the small droplets in the flow can significantly affect the measurement accuracy. The optical shadow method was used to measure the parameters and distribution of droplets around the bluff body in annular mist flow. The experimental results show that the velocity distribution of droplets upstream of the bluff body mainly depends on the gas superficial velocity. After passing through the bluff body, when the liquid loading capacity φl is<0.030, the droplet velocity changes from a concentrated single-peak to an uneven double-peak distribution. However, when φl ≥ 0.041, the droplet velocity distribution recovers to a single-peak distribution. The joint distribution of droplet diameter and velocity indicates that the change in velocity distribution is mainly caused by small droplets within the range of 0 to 20 μm, as large droplets are not easily lifted by vortices but can cause rapid dissipation of vortices. The experimental data quantitatively confirm the momentum transfer and transformation between droplets and the vortex flow field, and describe the motion dynamics of droplets in the flow field through the Stokes number (Stp) to analyze the interaction between droplets and vortices.