Date

5-25-2023

Department

School of Engineering

Degree

Doctor of Philosophy in Engineering (PhD)

Chair

Wayne Strasser

Keywords

CFD, Multiphase, Transonic, Non-Newtonian, PID

Disciplines

Mechanical Engineering

Abstract

The characterization of viscous, non-Newtonian slurry heating and atomization by means of internal wave excitation is presented for a twin-fluid injector. We detail mechanisms that enhance their disintegration in a novel process called “Wave-Augmented Varicose Explosions” (WAVE). Atomization of such fluids is challenging, especially at low gas-liquid mass ratios. Droplet production is further complicated when slurry viscosity varies widely; if viscosity levels are too high, atomization quality suffers, and an undesirable pressure drop restricts the flow. To mitigate, we introduce and demonstrate “Smart” atomization, a novel implementation of simultaneous proportional integral derivative (PID) control algorithms to accommodate dynamically and extensively changing fluid properties. Unlike a conventional twin-fluid injector, WAVE injects a cold annular slurry flow into a hot core steam flow, encouraging regular slurry waves to form inside the nozzle and producing bulk system pulsation at 1000 Hz. The Kelvin-Helmholtz instability dominates during wave formation, while transonic pressure effects dominate during wave collapse. Numerical simulations reveal three atomization mechanisms that are a direct result of wave formation: 1) wave impact momentum, 2) pressure buildup, and 3) droplet breakaway. The first two are the forces that exploit slurry irregularities to drive rupture. The third occurs as rising waves penetrate the central steam flow and droplets are stripped off. Two effervescent mechanisms are also provided as 1) surface deformation allows steam fingers to force through the wave, and 2) the wave collapses on itself, trapping steam. Both Rayleigh-Taylor and Kelvin-Helmholtz instabilities are self-amplified in a viscosity-shear-temperature instability cycle because the slurry’s viscosity is sensitive to both strain and temperature. Smart atomization is applied to the WAVE framework with two coupled PID controllers to improve atomization robustness. The first controller automates slurry flow based on atomizer pressure drop, while the second compensates for the newly adjusted phase momentum ratio and sets a new steam flow based on droplet size. Three tests with increasingly rigorous models were conducted to capture the response of this coupled controller system to a step increase in viscosity. Though atomization characteristics were drastically altered, for a 100-fold increase in slurry viscosity, the controllers successfully maintained consistent droplet size and slurry flow resistance.

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