10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Characterization of Droplets Injected into Hyperbaric Atmospheres by the Flow Blurring® Mechanism
LUIS MODESTO-LÓPEZ, Alfonso Gañán-Calvo, University of Seville
Abstract Number: 1548 Working Group: Aerosol Physics
Abstract In a general liquid atomization process a fraction of an energy input is transformed into surface energy. Particularly, in pneumatic atomization, the interaction of gas and liquid flows is typically accompanied by turbulent motions that lead to production of relatively small droplets.
An efficient liquid atomization method was developed by Gañán-Calvo (2005), known as Flow Blurring (FB). This method maximizes the surface area of the liquid flow at a minimum gas expense, thus resulting in a high atomization efficiency compared to conventional pneumatic techniques. The approach is also effective in preventing droplet coalescence. In a FB atomizer, an unexpected back-flow pattern in its interior, close to the atomizer outlet, produces small scale perturbations leading to an efficient mixing between the gas and liquid flows (see Gañán-Calvo, 2005; Modesto-López & Gañán-Calvo, 2018).
Typical FB atomizers are built with a simple yet robust design in which a liquid feeding tube is placed concentrically inside a gas feeding tube. The two fluids then interact in a zone nearby the outlet of the inner tube. Aerosol droplets, with a broad size distribution, leave the atomizer through a discharge orifice, spaced at a distance H from the tip of the liquid feeding tube. In these atomizers, the interaction of the liquid and gas flows is controlled by a geometrical parameter (φ), which is the ratio of H to the diameter (D) of the discharge orifice, as depicted in Gañán-Calvo (2005). FB atomizers find applications in many technological areas.
FB nozzles have been used in spectrometric techniques for generation of analyte droplets (Kovachev et al., 2009) and in atomization of biofuels (Simmons and Agrawal 2012). Recently, we have proposed a direct atomization of water into a combustion engine with FB nozzles, aiming at reduction of emissions (Modesto-López and Ganán-Calvo 2017). The approaches that use water in combustion engines include either direct injection or mixing with the fuel (Sahin et al., 2014). In both cases, the size of the droplets is a key parameter influencing the droplets’ evaporation timescale and their transport characteristics, and thus combustion efficiency. Most of the research on these topics has been carried out at ambient or relatively low pressure conditions. However, FB in high-pressure environments, where many processes occur, remain largely unexplored. Thus, a detailed characterization of droplet size is of significant importance to understand in those environments.
In this work, we study the characteristics of sprays injected by FB nozzles into a chamber where a high pressure atmosphere is maintained. We coupled real-time visual methods with light scattering techniques to obtain the size distribution and the speed profile of aerosol droplets in the vicinity of the FB nozzle. The key process parameters controlling FB atomization are the liquid flow rate, Q, the inlet gas pressure, Po, the chamber pressure, Pi, and thus the pressure difference, ΔP = Po - Pi. We also investigated a wide range of ΔP values for three different liquid flow rates to obtain a correlation in terms of dimensionless parameters.
The approach presented in this study may be a guideline for implementation of FB in high-pressure applications, for instance, in combustion technology.
References: [1] Kovachev, N. et al. (2009). Development and Characterization of a Flow Focusing Multi Nebulization System for Sample Introduction in ICP-Based Spectrometric Techniques. J. Anal. At. Spectrom., 24:1213–1221. [2] Gañán-Calvo, A.M. (2005) Appl. Phys. Lett., 86, 214101 (3pp). [3] Modesto-López, L. B. and Gañán-Calvo, A. M. (2017, August-September). Liquid Atomization by Flow Blurring® (FB) in a High-Pressure Environment for Combustion Applications. Paper presented at the European Aerosol Conference 2017, Zurich, Germany. [4] Modesto-López, L. B. & Gañán-Calvo, A. M. (2018) Aerosol Sci. Technol., 52(2), 198-208. [5] Rosell-Llompart J. and Gañán-Calvo A. M. (2008) Phys. Rev. E, 77, 036321 (10pp). [6] Sahin, Z. et al. (2014) Fuel, 115, 884–895. [7] Simmons, B. & Agrawal, K. A. (2012). Combust. Sci. Technol., 184, 660–675.