Secondary atomization of inelastic non-newtonian liquid drops in the bag and multimode regimes

Jonathan Rocha, Purdue University

Abstract

Secondary atomization of inelastic shear thinning non-Newtonian liquids in the bag and multimode regimes was studied. Six mixtures were formulated from deionized (DI) water, Avantor Performance Materials' USP grade 100% vegetable based glycerin, and Ashland's Carboxymethylcellulose (CMC-7MF or CMC-7HF). The resulting solutions had power law parameters flow behavior index, n, between 0.71 and 0.93 and consistency index, K, in the range of 0.0464 to 0.37 Pa·s n. The effective viscosity for each mixture was estimated using the power-law model and experimentally measured strain rates up to the initiation time. Secondary atomization was achieved using a continuous jet setup. Breakup events were captured using a Vision Research Phantom v7.3 high speed camera operated at >6600 fps. This typically yielded more than 100 frames for each breakup event. Post processing was performed using an in-house MATLAB code. Breakup was observed to occur in the bag and multimode regimes. The measurement approach was validated by comparing DI-water values with literature results. The flow conditions and liquid properties varied between: 10 < We < 50, 0.00212 < Oh < 0.41, 0.71 ≤ n ≤ 0.93, 0.0464 ≤ K ≤ 0.37 Pa·sn, 990 < ρL < 1210 kg/m3, and 0.065 < σ < 0.073 N/m. Data obtained using the MATLAB code includes: initiation time, cross-stream diameter, drop displacement, velocity and acceleration, plus the coefficient of drag at initiation time. The bag breakup time was measured, along with the corresponding rim diameter, bag length, displacement, and velocity. Many of these quantities exhibited peaks in the bag or bag-and-stamen regimes, with magnitudes that varied with liquid properties. Results from the videos show shear thinning, inelastic drop breakup modes share many morphological features with those for Newtonian liquid drops. The only minor differences are persistent ligaments throughout every stage of breakup and non-uniform bag growth in the bag breakup regime. The similarity between current and Newtonian drop results means the classical We versus Oh regime map remains valid for shear thinning, inelastic drops. Two other correlations were found to adequately act as alternate regime maps. These include We versus liquid Reynolds number and We versus Rayleigh-Taylor Wave number. Finally, the Taylor Analogy Breakup (TAB) model was applied to the current results to determine its accuracy when predicting shear thinning, inelastic drop deformation. The aerodynamic force term was altered to account for the increasing drop projected area and drop viscosity modeled using the approximated strain rate up to initiation time. Data from post processing was used in order to further improve the TAB model. The result was quantitative agreement between predictions and experiments to within 29% for initiation time and 36% for drop velocity at initiation time.

Degree

M.S.M.E.

Advisors

Sojka, Purdue University.

Subject Area

Mechanical engineering

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