Visualization and size-measurement of droplets generated by Flow Blurring® in a high-pressure environment

Abstract

Flow Blurring Ò (FB) atomization is a highly efficient method to produce aerosols. It originates from an unexpected turbulent back flow motion in the interior of the atomizer. The onset for the appearance of such pattern is dictated by a geometrical parameter, ', that is, the ratio of the distance from the tip of the liquid feeding tube to the discharge orifice (H), and the diameter of the discharge orifice (D). In this work, a FB atomizer with a nominal ' D 1/6 was used to produce water and ethanol droplets into pressurized environments (>1 MPa). The droplet size distributions and mean droplet speeds were investigated using (1) direct visualization with an ultra-high-speed video camera coupled with an automated droplet measurement (ADM) program and (2) using a light scattering instrument. Light scattering measurements, with water and ethanol, varying the driving pressure to produce the aerosol (DP), indicate a power dependence of »2/5 of the dimensionless mean droplet diameter (D/D o) on the dimensionless liquid flow rate (Q/Q o). At higher liquid flow rate, the optical resolution of the droplets is improved compared to lower volumetric flow rates, thus facilitating analyses with the ADM program. The approach outlined herein provides a guideline for characterization and implementation of the FB technology in high-pressure applications.

On the Ejection of Filaments of Polymer Solutions Triggered by a Micrometer-Scale Mixing Mechanism

“…H is the distance from the tip of the inner tube (liquid feeding tube) to the discharge orifice and is the diameter of that orifice, which is typically the diameter of the inner tube too (see Figure 1 ). Flow Blurring atomizers have generally been used to produce droplets and aerosols from Newtonian liquids such as water, alcohols, polyols, glycols, oils or fuels in general [ 14 , 17 , 19 , 20 , 21 , 22 ]. Nevertheless, we have extended its application to the fragmentation of polymeric solutions, which exhibit a more complex rheology.…”

“…The rheology of polymer solutions depends on several factors such as polymer molecular weight, concentration, type of solvent, temperature, and pressure. Generally, based on concentration polymer solutions are classified as: dilute, semidilute, and concentrated [ 22 ], as depicted in the illustration of Figure 2 . In the first case, in dilute solutions, short-range interactions of polymer chains cause them to assemble into coils, which are intricate structures that look like “spaghetti”.…”

“…The entanglements develop from the interpenetration of random-coil polymer chains and may be quantified by an entanglement concentration, . Finally, in the case of concentrated solutions, and polymer coils strongly interact with each other and may develop entanglements as well [ 22 ]. In sum, the relationships between , , and are fundamental to determine whether the polymer solutions would form filaments during ejection.…”

Micromixing with In-Flight Charging of Polymer Solutions in a Single Step Enables High-Throughput Production of Micro- and Nanofibers

“…Typical values of filament diameter achieved with this method are of the order of 150 μm, which are ejected with mean speeds of approximately 80–100 m/s. 32 , 39 Previous analyses have shown that for a range of viscosities and liquid flow rates the mean as-ejected filament diameter, D f , is determined by the thickness of a liquid boundary layer (δ) that develops in the interior of the atomizer, 37 , 40 in the vicinity of its exit orifice of diameter D as depicted in Figure 1 . D f is calculated with a nondimensional relationship (see Figure 8 in Ramos-Escobar et al 37 and analyses therein): where D f * and Q * are nondimensional quantities, filament diameter, and liquid flow rate, respectively, and K is a prefactor of order unity.…”

“… 32 − 36 The atomizer consists of two concentric capillaries in which a gas current radially implodes into the inner tube carrying the liquid, thus triggering the vigorous mixing and causing the disintegration of the liquid bulk into smaller structures. These ejecta may be comprised of either droplets or filaments, depending on the viscous characteristics of the liquid 32 , 34 , 37 , 38 (see Figure 1 a). That is, micromixing of low-viscosity Newtonian liquids, such as water, results in ejection of droplets, i.e., a spray.…”