Mass Flow Scaling of Gas-Assisted Coaxial Atomizers

Simon Wachter,Tobias Jakobs,Thomas Kolb

doi:10.3390/app12042123

Abstract

This study aims to derive basic principles for liquid mass flow scaling of gas-assisted coaxial nozzles. Four liquid mass flow steps were investigated in the range of M˙liq = 20–500 kg·h−1, applying four atomizers with similar geometry designed at Weaero= const. High-speed camera and phase Doppler anemometer were utilized to detect the local droplet size distribution. To estimate a reliable measurement plane, a detection method and determination according to the free jet theory was used. The resulting droplet size was analyzed, applying the aerodynamic Weber number, as well as the gas momentum flow. An empirical model was derived out of the measured data, which allows for liquid mass flow scaling when process parameters such as GLR, liquid mass flow, and required Sauter mean diameter are specified. The model was developed as a first step towards liquid mass flow scaling of gas-assisted coaxial atomizers within the investigated range of operating conditions.

Highlights

Gas-assisted coaxial atomizers with central liquid jets are commonly utilized in industrial applications such as spray drying and coating [1], food-processing [2], combustion [3], and gasification processes [4]
This study aims to lay the groundwork for liquid mass flow scaling of gas-assisted coaxial atomizers
Four liquid mass flow steps (20/50/100/500 kg·h−1), each operated at Weaero = 250/500/750/1000, were investigated in terms of spray quality (D32, ID32,m) and primary breakup

Summary

Introduction

Gas-assisted coaxial atomizers with central liquid jets are commonly utilized in industrial applications such as spray drying and coating [1], food-processing [2], combustion [3], and gasification processes [4]. Despite the noted variety of possible applications, physical as well as atomization phenomena forming a droplet collective from a liquid jet through a high-velocity gas stream are not yet fully understood. As this topic is of fundamental interest in the field of two-phase flows, extensive research was already performed on the morphological classification of liquid jet breakup [5], the secondary breakup of liquid fragments [6,7], or spray characterization [8,9]. After adjustment of the lab-scale atomizer to produce an adequate spray for the later process, the upscaling step of mass flows toward industrial conditions was performed empirically in most cases, as discussions on scaling rules in literature are scarce

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Conclusion