Spray Characterization of non-newtonian Impinging Jets Using Digital In-Line Holography.

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1 ILASS Americas 28th Annual Conference on Liquid Atomization and Spray Systems, Dearborn, MI, May 2016 Spray Characterization of non-newtonian Impinging Jets Using Digital In-Line Holography. N. S. Rodrigues *, J. Gao, J. Chen and P. E. Sojka M. J. Zucrow Laboratories Purdue University West Lafayette, IN USA Abstract Impinging jets are a common method for atomizing propellants in liquid rocket engines. Recent work has investigated improving rocket engine safety while also improving the performance by using non-newtonian liquids. Since viscosity hinders the atomization process, liquids that exhibit strong shear-thinning behavior are required. The two non-newtonian liquids considered in this work were solutions of carboxymethylcellulose (CMC) and DI-water having 0.8 wt.- % CMC-7MF and 1.4 wt.-% CMC-7MF. The Bird-Carreau rheological model was adopted to describe the shearshinning behavior. A generalized Bird-Carreau jet Reynolds number was used as the primary independent variable. To that end, spatially resolved, three-dimensional (3D) spray characteristics are acquired to evaluate the efficacy of non-newtonian liquid atomization. A double-exposure digital in-line holography (DIH) system and a hybrid method image analysis program is used in this work to extract 3-D distributions of droplet size and drop velocity. Spray characteristics using DI water are also considered to serve as a reference for the non-newtonian spray cases. * Corresponding author: neilrodrigues@asme.org

ILASS Americas 28th Annual Conference on Liquid Atomization and Spray Systems, Dearborn, MI, May 2016 Introduction The impinging jet atomizer is commonly used in liquid rocket engines to atomize the

2 ILASS Americas 28th Annual Conference on Liquid Atomization and Spray Systems, Dearborn, MI, May 2016 Introduction The impinging jet atomizer is commonly used in liquid rocket engines to atomize the bulk liquid propellants [1]. The primary atomization mechanism for an impinging jet doublet begins with two cylindrical jets colliding at an oblique angle to form a liquid sheet that is perpendicular to the plane containing the momentum vectors of the two jets. Instabilities cause the liquid sheet to fragment into ligaments, and the ligaments to then further break up into drops. Figure 1 provides a shadowgraph from Rodrigues et al. [2] of a DI-water spray to illustrate typical behavior. In order to account for shear-thinning behavior, the Bird-Carreau rheological model is used for the liquids sprayed during this study (1) where η( ) BC is the effective viscosity as a function of the strain rate, η 0 is the zero-strain rate viscosity, η is the infinite-strain rate, n is the flow behavior index and describes the rapidly decreasing liquid response time to a change in strain rate [11]. Impinging jet atomization studies typically use the jet Re and We as the primary scaling parameters. The Reynolds number must be modified for non-newtonian liquids to account for the strain-rate dependency of the effective viscosity [13] Re j,genbc L U j d j n1 1 3n 1 2 8U j 2 4n d j 0. (2) 3n 1 4n where the previously listed Bird-Carreau parameters are included, along with the liquid density, ρ L, jet velocity, U j, and jet diameter d j. The expression for jet We j is Figure 1. Shadowgraph of impinging jet break-up using DI-water [2]. Newtonian liquids, such as water, have traditionally been used to study the atomization produced by impinging jets [3-6]. However, in recent years there has been increased interest in investigating the impinging jet atomization of non-newtonian liquids [7-10]. The viscosity of non-newtonian liquids is complex, and at that very least varies with strain rate. Newtonian liquids, on the other hand, maintain a constant value of viscosity regardless of strain rate [11]. Shear-thinning, non-newtonian liquids that do not flow easily unless under pressure are advantageous for applications such as liquid rocket propulsion. This is because containment and cleanup would be more manageable in the event of a spillage. The difficulty with atomization, due to the increased effective viscosity of the liquid, is the main disadvantage with using non-newtonian liquids [12]. Therefore, studying the spray characteristics is needed to evaluate the efficacy of these non-newtonian liquids to produce desirable atomization characteristics. We j U 2 d L j j. (3) where the is the liquid-air surface tension. Shadowgraphy is often used to study impinging jet spray formation [14-16]. Spray characteristics such as sheet breakup length and drop diameter are typically extracted from the images. Impinging jet sprays drop sizes, as well as sizes and velocities, have also been studied using laser diffraction methods, and phase Doppler anemometry (PDA) [17-19]. A difficulty when using any of these techniques is obtaining spatially-resolved measurements. Two-dimensional (2D) diagnostic techniques such as shadowgraphy cannot provide spatially resolved 3D data. Pointwise measurement techniques, such as PDA, require significant experimental repetitions to obtain spatially resolved measurements. Line-of-sight data must first be deconvolved into point data, at which time it can be used to provide 3D views. Recently, digital in-line holography (DIH) has been applied to quantify secondary atomization processes such as aerodynamic breakup of a drop and drop impact on a thin liquid film [20-22]. These results, and others, have demonstrated that DIH is capable of providing 3D measurements of droplet size and velocity distributions, as well as shapes and kinematics of non-spherical structures. There have been a few reports of DIH applied to primary atomization [23-25]. However, due to the inability of DIH to probe denser particle fields, these studies are

3 limited to relatively sparse sprays or sparse regions of a spray. While more recent holographic spray investigations do have a limitation on optical density, they are superior to earlier holographic measurements of impinging jet sprays which relied on optical holography [26-27]. This was essentially a 2D characterization due to the formidable task of mechanically scanning the reconstruction volume. In this study, DIH and its digital refocusing ability was used to characterize non-newtonian impinging jet sprays for the first time. Drop size distribution, 3D position, and drop velocity are reported as functions of jet Re and We. Experimental Method Two solutions of CMC-7MF (200 kda) Carboxymethylcellulose dissolved in DI-water were used during this investigation: 0.8 wt.-% CMC-7MF and 1.4 wt.- % CMC-7MF. The solutions were mixed using a lowshear mixer and left to stir until determined to be homogenous by visual inspection. Experimental measurements for viscosity at a range of strain rates were obtained using both rotational and capillary rheometers. The shear-thinning non-newtonian behavior was characterized using the Bird-Carreau rheological model, with the relevant parameters listed in Table 1. The solution surface tensions were determined using a du Noüy ring Tensiometer, with that for each liquid observed to be close to the literature value for water (γ = N/m). Therefore, the literature value was used for all We calculations. Further details on the bulk and interfacial rheological measurements can be found in Rodrigues [28]. Table 1. Bird-Carreau rheological parameters for 0.8 wt.-% CMC-7MF and 1.4 wt.-% CMC-7MF solutions [14]. Parameter 0.8 wt.-% 1.4 wt.-% CMC-7MF CMC-7HF η 0 [Pa-s] ± ± η [Pa-s] n [-] ± ± λ [s] ± ± Pure DI-water was also sprayed as a reference liquid. Its Bird-Carreau parameters are: η 0 =η =0.001 Pas, n=1, and λ=0 s [28]. The facility of Rodrigues et al. [14] was used to create impinging jet atomization during this study. A schematic is presented as Fig. 2. The impingement full angle, 2θ, was fixed at 100, while the free jet length-to-orifice diameter ratio, x/d 0, was held at 60. The internal lengthto-orifice diameter ratio, L/d 0, was 20 and orifice diameter, d 0, was always mm. Figure 2. Experimental apparatus. The mean jet velocity, U j, was calculated by measuring the liquid mass collected in a vessel. Values obtained via this method showed good agreement (< 3% difference) with jet velocities obtained using DIH. The operating pressure was varied for the liquids tested in order to control Re j,gen-bc and We j, via the mean jet velocity. Table 2 presents the test conditions for this work in terms of their respective dimensionless numbers. The Kline-McClintock approach was used to calculate the percent uncertainty for the generalized Bird-Carreau jet Re and We [29]. Table 2. Test conditions for present work. Parameter Re j,gen-bc [-]x10 3 We j [-]x wt.-% CMC-7MF 1.4 wt.-% CMC-7HF 7.81 ± ± ± ± 0.12 DI Water 6.65 ± ± The DIH setup is shown in Fig. 3. A double-pulse frequency-doubled Nd:YAG laser served as the light source. The laser beam was spatially filtered, split into two illuminating beams (View 1 and View 2 in Fig. 3), then directed at two regions of the impinging jet spray. Since the impinging jet doublet was mounted on a 3-axis precision translation slide, different regions of the spray could be easily investigated by traversing the injector. Droplets in the path of the illuminating beam scatter/diffract light and the interference pattern between the scattered/diffracted light and the undisturbed illuminating light was recorded as a hologram by the two CCD cameras ( pixels with a pixel size of 9 9 μm 2). The two cameras provided a sampling volume as

large as 4.8 cm (y-direction) 3.6 cm (x-direction) 30 cm (z-direction, depth). The impingement point was set as the origin of coordinates.

Both cameras were configured in double-exposure mode and synchronized with the doublepulse laser beams so that time sequential holograms could be recorded and used for velocity measurement.

$The numerical reconstruction was performed using the Rayleigh-Sommerfeld diffraction equation [30]. Reconstruction of the holograms at an arbitrary depth corresponding to the axial positions in Figs.$ 4(a) and 4(b) are resented in Fig. 4(c) and Fig. 4(d), respectively. The droplet size and positional information encoded in the hologram was retrieved using the hybrid method [31-32].

4(a) and 4(b) are resented in Fig. 4(c) and Fig. 4(d), respectively. The droplet size and positional information encoded in the hologram was retrieved using the hybrid method [31-32].

However, it should be noted that spherical particles overlapping in the transverse direction might also have been removed due to the threshold limit.

4 large as 4.8 cm (y-direction) 3.6 cm (x-direction) 30 cm (z-direction, depth). The impingement point was set as the origin of coordinates. The lower end of the dynamic range for drop diameter measurement was approximately 30 μm. Both cameras were configured in double-exposure mode and synchronized with the doublepulse laser beams so that time sequential holograms could be recorded and used for velocity measurement. (a) 5 mm Figure 3. DIH schematic. Two sample holograms, and corresponding reconstructions, for 1.4 wt.-% CMC-7MF at Re j,gen-bc =6,450 and We j =2,760 are presented in Fig. 4. In View 1, shown in Fig. 4(a), the ligaments had not fully broken up into droplets at y=9.5 cm. However, drop formation was observed further downstream at y=29.2 cm, as shown in Fig. 4(b). The numerical reconstruction was performed using the Rayleigh-Sommerfeld diffraction equation [30]. Reconstruction of the holograms at an arbitrary depth corresponding to the axial positions in Figs. 4(a) and 4(b) are resented in Fig. 4(c) and Fig. 4(d), respectively. The droplet size and positional information encoded in the hologram was retrieved using the hybrid method [31-32]. A threshold of circularity for the shape of the detected particles was used to eliminate possible erroneous measurements. However, it should be noted that spherical particles overlapping in the transverse direction might also have been removed due to the threshold limit. Drops in a hologram volume were identified by their 3D coordinates and size. Drop tracking obtained from sequential holograms provided velocities, with the match probability method used for particle pairing [33]. Results and Discussion Shadowgraphs of impinging jet atomization are presented in Figs. 5 and 6 for 0.8 wt.-% CMC-7MF and 1.4 wt.-% CMC-7MF, respectively. The resulting spray formation can be described as forming a ligament web pattern from the liquid sheet [14], with ligaments separating from the web at further downstream distances, and then undergoing their own instabilities to form drops. The axial location where liquid sheet breakup occurs is not easily discernable. (b) (c) (d) Figure 4. (a) Holograms obtained from View 1, and (b) from View 2; (c) Reconstruction of the enclosed region from View 1 at an arbitrary depth, (d) and the enclosed region from View 2 at an arbitrary depth. Spatially resolved drop diameters for the 0.8 wt.-% CMC-7MF spray are presented for axial locations y=9.5 and y= 9.7 cm in Figs. 7(a) and 7(b), respectively. Sample sizes are 514 and 2,108 drops, respectively. From these figures drops are observed to become more disperse across the z-axis with greater axial distance away from the impingement point. Figure 8 presents spatially resolved drop diameters for the 1.4 wt.-% CMC-7MF spray at y=19.7 cm. The sample size is 1,472 drops.

5 2 mm Figure 5. Impinging jet spray formation for 0.8 wt.-% CMC-7MF at Re j,gen-bc =7,810 and We j =2,760 [14]. Figure 6. Impinging jet spray formation of 1.4 wt.-% CMC-7MF at Re j,gen-bc =6,450 and We j =2,760 [14]. (a) 1 mm (b) Figure 7. Spatially resolved drop diameter obtained for 0.8 wt.-% CMC-7MF spray for Re j,gen-bc =7,810 and We j =2,760 at: (a) y=9.5 cm, (b) y=19.7 cm. As mentioned in the previous section, drop formation from ligaments was not present for this test condition at an axial location of y=9.5 cm. This is ascribed to viscous damping of breakup increasing with the higher concentration of CMC-7MF. The increased role played by viscosity was also observed in the formation of larger drops, particularly those greater than 700 μm.

6 Figure 8. Spatially resolved drop diameter obtained using DIH of 1.4 wt.-% CMC-7MF spray at Re j,gen-bc =6,450 and We j = 2,760 for axial location at y = 19.7 cm View 2. A slight asymmetry in drop spatial distribution about the z-axis is observed in both Figs. 7 and 8. This may be due to the density of the particle field. Another possible explanation is that drops further from the CCD plane (located at z=-484 mm) were less distinct and therefore more difficult to detect. Furthermore, although the two jets were targeted at the impingement point, even small deviations in alignment may affect the orientation of the spray field. Number, f 0, area, f 2, and volume, f 3, pdfs are also presented. For the 0.8 wt.-% CMC-7MF case, the pdfs shift to the left as y increases from 9.5 (Fig. 9) to 19.7 (Fig, 10) cm. This indicates atomization is continuing, and may be due to ligament or drop breakup (secondary atomization). This is supported by representative diameter data for D 10, D 32, and MMD, presented in Table 3, which are all smaller at y=19.7 cm than at y=9.5 cm Re j,gen-bc = 7,810 and We j =2,760 f 0 f 2 f Drop Diameter [ m] Figure 9. Number, f 0, area, f 2, and volume, f 3, pdfs versus drop diameter for 0.8 wt.-% CMC-7MF spray with Re j,gen-bc =7,810 and We j =2,760 at y=9.5 cm Re j,gen-bc = 7,810 and We j =2,760 f 0 f 2 f Drop Diameter [ m] Figure 10. Number, f 0, area, f 2, and volume, f 3, pdfs versus drop diameter for 0.8 wt.-% CMC-7MF spray with Re j,gen-bc =7,810 and We j =2,760 at y=19.7 cm. D 10, D 32, and MMD for the 1.4 wt.-% CMC-7MF spray at y=19.7 cm were also observed to be greater than those for the 0.8 wt.-% CMC-7MF spray at the same axial location. This can be attributed to the greater viscous damping of instabilities in the 1.4 wt.-% spray. Number, surface area, and volume pdfs for the 1.4 wt.-% spray are presented in Fig. 11. A lower probability density for the smaller drops was observed when compared to that of 0.8 wt.-%. Since large diameters heavily influence calculation of the representative diameters, the presence of a few large diameters (>700 μm) was likely responsible for the greater D 32, and MMD values. Measurements of a DI water spray are presented in Fig. 11 at Re j,gen-bc =6,650, and We j =877, for comparison with those of the non-newtonian sprays. The DI-water measurements were first reported by Gao et al. [33]. Water spray f 0, f 2, and, f 3, are presented in Fig. 12 for y=9.5 cm and Fig. 13 for y=19.7 cm.

7 Table 3. Representative diameters D 10, D 32, and MMD for liquids and test conditions included in this study. Parameter 0.8 wt.-% CMC-7MF y=9.5 cm 0.8 wt.-% CMC-7MF y=19.7 cm 1.4 wt.-% CMC-7MF y=19.7 cm DI-Water y=9.5 cm DI-Water y=19.7 cm D 10 [μm] D 32 [μm] MMD [μm] Table 3 characteristic size calculations were performed using a 5251 drop sample for the 0.8 wt.-% spray at y=9.5 cm, a 17,399 drop sample for the 0.8 wt.-% spray at y=19.7 cm, a 12,997 drop sample for the 1.4 wt.- % spray at y=19.7 cm, a 23,940 drop sample for the DIwater spray at y=9.5 cm, and a 22,407 drop sample for the DI-water spray at y=19.7 cm. Comparing the resulting non-newtonian characteristic sizes with those for DI-water yield an interesting observation D 32 and MMD values for the DI-water spray are greater than those of the 0.8 wt.-% spray at both y=9.5 and y=19.7 cm. On the surface this is surprising since non-newtonian viscous behavior is known to hinder breakup and therefore result in larger drop sizes. However, considering Re j,gen-bc for the test cases shows that the inertial-toviscous forces ratios for the 0.8 wt.-% CMC spray are actually greater than those for the DI water spray. Furthermore, We j shows that the inertial-to-capillary forces ratio for the 0.8 wt.-% CMC spray is more than three times that of the DI-water spray. This suggests smaller drop sizes for the 0.8 wt.-% CMC spray. The 1.4 wt.-% CMC-7MF spray D 32 and MMD characteristic diameter values are observed to be greater than those of both the 0.8 wt.-% spray and of DI water at y=19.7 cm. This is expected, and is attributed to the inertial-to-viscous forces of the 1.4 wt.-% CMC-7MF spray, observed through Re j,gen-bc, being lower than that for the other two liquids. This leads to larger drops. Figure 14 presents typical spatially resolved drop velocities at (a) y=9.5 cm and (b) y=19.7 cm. These data show the expected lower velocities at y=19.7 cm, due of course to aerodynamic drag. Only the in-plane velocities are presented in Fig. 14 as the out-of-plane velocities have significantly larger uncertainty Re j,gen-bc = 6,450 and We j =2,760 f 0 f 2 f Drop Diameter [ m] Figure 11. Number, f 0, area, f 2, and volume, f 3, pdfs versus drop diameter for 1.4 wt.-% CMC-7MF spray with Re j,gen-bc =6,450 and We j =2,760 at y=19.7 cm Re j,gen-bc = 6,650 and We j = 887 f 0 f 2 f Drop Diameter [ m] Figure 12. Number, f 0, area, f 2, and volume, f 3, pdfs versus drop diameter for DI-water sprays with Re j,gen- BC=6,650 and We j =877 at y=9.5 cm. Summary and Conclusions The first DIH measured impinging jet spray sizes and velocities are reported for two non-newtonian liquids, with the hybrid method of image analysis [31] used to identify individual droplets. Velocities were obtained from double-pulsing the source laser and measuring drop displacements over the known time interval. Results are presented for two distances downstream of the impingement point. Spray characteristics for DI-water were also acquired to serve as a reference for the non-newtonian spray cases.

0.015 0.012 0.009 0.006 0.003 0 Re j,gen-bc = 6,650 and We j = 887 f 0 f 2 f 3 0 200 400 600 800 1000 1200 Drop Diameter [ m] Figure 13.

This can be attributed to a greater level of drop formation from ligament breakup at axial distances further downstream from the impingement point.

8 Re j,gen-bc = 6,650 and We j = 887 f 0 f 2 f Drop Diameter [ m] Figure 13. Number, f 0, area, f 2, and volume, f 3, pdfs versus drop diameter for DI-water spray with Re j,gen- BC=6,650 and We j =877 at y=19.7 cm. (a) at y = 9.5 cm. This can be attributed to a greater level of drop formation from ligament breakup at axial distances further downstream from the impingement point. Secondary breakup of drops is also a possible explanation. Characteristic diameters for the 1.4 wt.-% CMC- 7MF at y = 19.7 cm were larger than those for 0.8 wt.-% spray at the same location. This was expected and is ascribed by the increased effective viscosity for the 1.4 wt.- % spray. At first glance, comparison of the 0.8 wt.-% CMC- 7MF spray characteristic diameters with those for DIwater are surprising because the latter values might be anticipated to be smaller than the former. Further analysis shows that Re j,gen-bc for the 0.8 wt.-% CMC-7MF spray is greater than that of the DI-water spray (due to different jet velocities), a fact that helps explain the lower values for 0.8 wt.-% spray D 32 and MMD. This explanation is buttressed by the inertial-to-capillary force ratio for the 0.8 wt.-% CMC spray being over three times greater than that for the DI water spray, which will lead to reduced drop sizes. Nomenclature D 10 arithmetic mean diameter [μm] D 32 Sauter mean diameter [μm] f 0 number probability density function f 2 area probability density function f 3 volume probability density function MMD mass-median diameter [μm] n Bird-Carreau flow behavior index [-] pdf probability density function Re j,gen-bc generalized Bird-Carreau jet Reynolds number [-] U j mean jet velocity [m/s] We j jet Weber number [-] γ surface tension [N/n] η 0 Bird-Carreau zero strain rate viscosity [Pa-s] η Bird-Carreau infinite strain rate density [Pa-s] λ Bird-Carreau time constant [s] L liquid density [kg/m 3 ] Acknowledgements The research presented in this paper was made possible with the financial support of the U.S. Army Research Office under the Multi-University Research Initiative Grant Number W911NF (b) Figure 14. Drop velocities for DI-water spray at Re j,gen- BC=6,650 and We j =877 at: (a) y=9.5 cm and (b) y=19.7 cm. For the 0.8 wt.-% CMC-7MF spray, smaller characteristic drop diameters were observed at y = 19.7 cm than References 1. Humble, R.W., Henry, G.N., Larson, W.J., Space Propulsion Analysis and Design, McGraw-Hill, Rodrigues, N.S., Kulkarni, V., Gao, J., Chen, J., Sojka, P.E., Experiments in Fluids 56(50) (2015). 3. Heidmann, M.F., Priem, R.J., and Humphrey, J.C., A Study of the Sprays Formed by Two Impinging

9 Jets, National Advisory Committee for Aeronautics, Technical Note 3835, Ibrahim, E.A., and Przekwas, E.A., Physics of Fluids A: Fluid Dynamics, 3(12): (1991). 5. Ryan, H.M, Anderson, W.E, Pal, S., and Santoro, R.J., Journal of Propulsion and Power 11(1): (1995). 6. Li R., and Ashgriz, N., Physics of Fluids, 18(8) (2006). 7. Baek, G., Kim, S., Han, J., and Kim, C., Journal of Non-Newtonian Fluid Mechanics 166: (2011). 8. Yang, L.J., Fu, Q.F., Qu, Y.Y., Gu, B., and Zhang, M.Z., International Journal of Multiphase Flow 39:37-44 (2012). 9. Mallory, J.A., and Sojka, P.E., Atomization and Sprays 24(5): (2014). 10. Mallory, J.A., and Sojka, P.E., Atomization and Sprays 24(6): (2014). 11. Morrison, F., Understanding Rheology, Oxford University Press, Nathan, B. and Rahimi, S., Combustion of Energetic Materials, Begel House, p , Mallory, J.A., and Sojka, P.E., 24 th European Conference on Liquid Atomization and Spray Systems, Estoril, Portugal, September Rodrigues, N.S., Kulkarni, V., Gao, J., Chen, J., and Sojka, P.E., ILASS Americas 27th Annual Conference of Liquid Atomization and Spray Systems, Raleigh, NC, May Rodrigues, N.S., Mallory, J.A., Sojka, P.E., 51st AIAA/SAE/ASEE Joint Propulsion Conference, Orlando, July Rodrigues, N.S. and Sojka, P.E., ASME 2015 International Mechanical Engineering Congress and Exposition, Houston, November Rodrigues, N.S. and Sojka, P.E., 52 nd Aerospace Sciences Meeting, National Harbor, MD, January Rodrigues, N.S. and Sojka, P.E., ILASS Americas 27th Annual Conference of Liquid Atomization and Spray Systems, Raleigh, NC, May Rodrigues, N.S., Gao, J., Chen, J., and Sojka, P.E., ASME 2015 International Mechanical Engineering Congress and Exposition, Houston, November Gao, J., Guildenbecher, D.R., Reu, P.L., and Chen, J., Optics Express 21: (2013). 21. Guildenbecher, D.R, Engvall, L., Gao, J., Grasser, T.W., Reu, P.L., and Chen, J., Experiments In Fluids 55: 1-9 (2014). 22. Gao, J., Rodrigues, N.S., Sojka, P.E., and Chen, J., ASME 4th Joint US-European Fluids Engineering Division Summer Meeting, Chicago, August Lee, J., Sallam, K.A., Lin, K.C., and Carter, C.D., Journal of Propulsion and Power 25: (2009). 24. Lu, Q.N., Chen, Y., Yuan, R., Ge, B., Gao, Y., and Zhang, Y., Applied Optics 48(36): (2009). 25. Yang, Y., and Kang, B.S., Optics and Lasers in Engineering 49: (2011). 26. Kang, B.S., Shen, Y.B., and Poulikakos, D., Atomization and Sprays 5(4): (1995). 27. Kang, B.S., and Poulikakos, D., Journal of Propulsion and Power 12(2): (1996). 28. Rodrigues, N.S., Impinging Jet Spray Formation Using Non-Newtonian Liquids, Purdue University M.S. Thesis, Kline, S.J., and McClintock, F.A., Mechanical Engineering 75:3-8 (1953). 30. Katz, J., and Sheng, J., Annual Review of Fluid Mechanics 42: (2010). 31. Guildenbecher, D.R., Gao, J., Reu, P.L., and Chen, J., Applied Optics 52: (2013). 32. Baek, S.J. and Lee, S.J., Experiments in Fluids 22: (1996). 33. Gao, J., Rodrigues, N., Sojka, P., and Chen, J., Bulletin of the American Physical Society 59, San Francisco, November 2014.

ILASS Americas 27th Annual Conference on Liquid Atomization and Spray Systems, Raleigh, NC, May 2015

ILASS Americas 27th Annual Conference on Liquid Atomization and Spray Systems, Raleigh, NC, May 2015 Non-Newtonian Impinging Jet Spray Formation at Low Generalized Bird-Carreau Jet Reynolds Numbers N.