Effect of Solid Particles on Droplet Size Applying the Time-Shift Method for Spray Investigation

Simon Wachter,Thomas Kolb,Tobias Jakobs

doi:10.3390/app10217615

Abstract

This study investigated the influence of solid particles on primary breakup and resulting droplet size for different process parameters. Two sets of Newtonian fluids (each consisting of one pure liquid and one suspension at the same respective viscosity) were used, for isolated investigation of solid particles on spray formation independent of liquid viscosity. The spray was recorded by a high-speed camera and a SpraySpy® system based on the time-shift effect, while a commonly used Spraytec® laser diffraction analyzer was employed for validation. An external-mixing twin-fluid atomizer was operated at different gas velocities and corresponding GLR at constant liquid mass flow. For the investigated suspensions an increased Sauter mean diameter was detected, compared to the pure liquids with identical dynamic viscosity. This effect was explained by the tensile strength stabilizing the suspension droplets.

Highlights

Spray processes are often applied in industrial production, the influence of process conditions and liquid properties on atomization is not yet fully understood
The comparison of the local d32 values revealed by the time shift-based system and the integral d32 values revealed by state-of-the-art laser diffraction measurement technique is presented
This study investigated the influence of solid particles on spray formation for different process parameters

Summary

Introduction

Spray processes are often applied in industrial production, the influence of process conditions and liquid properties on atomization is not yet fully understood. Knowledge remains limited on the twin-fluid atomization of suspensions with different viscosities and solid mass fractions, as commonly used in the food industry (e.g., in spray drying), gas cleaning or in entrained flow gasifiers (EFG). Investigations of droplet size distributions in suspension sprays have typically used the laser diffraction technique due to the opacity of the emerging droplets [1,2,3]. Applying this measuring technique results in an integral droplet diameter that represents the spray quality in the measuring plane. Suspensions mostly exhibit non-Newtonian behavior, wide particle size distributions and varying solid mass fractions [4,5]

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