Spray Formation of Herschel--Bulkley Fluids using Impinging Jets

The impinging jet spray formation of two non-Newtonian, shear-thinning, Herschel--Bulkley fluids was investigated in this work. The water-based gelled solutions used were 1.0 wt.-{\%} agar and 1.0 wt.-{\%} kappa carrageenan. A rotational rheometer and a capillary viscometer were used to measure the strain-rate dependency of viscosity and the Herschel--Bulkley Extended (HBE) rheological model was used to characterize the shear-thinning behavior. A generalized HBE jet Reynolds number \textit{Re}$_{\mathrm{j,gen-HBE}}$ was used as the primary parameter to characterize the spray formation. A like-on-like impinging jet doublet was used to produce atomization. Shadowgraphs were captured in the plane of the sheet formed by the two jets using a CCD camera with an Nd:YAG laser beam providing the back-illumination. Typical behavior for impinging jet atomization using Newtonian liquids was not generally observed due to the non-Newtonian, viscous properties of the agar and kappa carrageenan gels. Instead various spray patterns were observed depending on \textit{Re}$_{\mathrm{j,gen-HBE}}$. Spray characteristics of maximum instability wavelength and sheet breakup length were extracted from the shadowgraphs.