Emulsions Using a Vortex-Based Cavitation Device: Influence of Number of Passes, Pressure Drop, and Device Scale on Droplet Size Distributions

Abstract

Liquid−liquid emulsions are used in a variety of industry sectors, including personal care, home care, food, and nutrition. The development of compact and modular systems and devices for creating emulsions with desired droplet size distribution (DSD) is becoming increasingly important. In this work, we have shown use of vortex-based cavitation devices for producing emulsions at nominal flow rate of 1 LPM and 20 LPM. We present new experimental results providing quantitative information on influence of multiple passes through the vortex based hydrodynamic cavitation (HC) device, type of oil and device scale on the breakage process and resulting DSDs. Multiple pass experiments were performed for generating oil-in-water emulsions containing 5 and 15% of oil. Rapeseed oil (RO) and tetrachloroethylene (TCE) were used as oil phases with densities of 915 and 1620 kg/m 3 , respectively. The effect of pressure drop across the HC device in the range of 50−250 kPa on DSD was examined. The HC device was shown to exhibit significant higher efficiency compared to alternative emulsion making devices (i.e., homogenizers, venturi, and orifice-based HC devices), and the Sauter mean drop size was found to reduce from 66 μm to less than 2 μm after about 50 passes in all the device scales. The DSD of the RO−water system showed a bimodal nature, whereas monomodal DSD was found for TCE−water system. Preliminary simulations using the computational fluid dynamics−population balance model (CFD-PBM) models developed in the previous work indicated the inadequacy of developed models to capture the influence of cavitation on DSDs. By carrying out Hinze scale analysis of bimodal DSD, we for the first time showed the existence of two different mechanisms (one based on conventional turbulent shear and the other based on collapsing cavities) of droplet breakage in HC devices. The order of magnitude of turbulence energy dissipation rates generated due to collapsing cavity estimated using Hinze scale analysis showed good agreement with the values reported from cavity dynamics models. The presented experimental results and analysis will be useful for researchers and engineers interested in developing computational models and compact devices for producing emulsions of the desired DSD.

Liquid‐Liquid Emulsion Produced by 3D‐Printed Vortex‐Based Hydrodynamic Cavitation Device

“…The nature of the DSD was bimodal at lower passes, and the bimodal nature of the DSD vanished beyond 50 passes. A detailed analysis of and possible reasons for bimodal nature in initial passes are described by Thaker and Ranade 24. The volume fraction of small droplets was found to be marginally lower in the 3D‐printed diode than in the VMC‐machined diode at 200 passes.…”

“…This indicates that the droplet breakage rate and probability of droplet breakage were the same despite the difference in Eu between the two devices. The measured trend of d 32 with different number of passes obtained from both devices can be represented by using empirical correlation developed by Thaker and Ranade 24 as Eq. 1: …”

“…Recently, Thaker and Ranade 24 investigated the effect of multiphase passes, inlet pressure drops, device scales, and oil‐water systems (rapeseed oil (RO)‐water and trichloroethylene‐water) on the DSD. They compared the efficiency of laboratory‐scale (emulsion production: 1 liter per minute (LPM)) and bench scale (emulsion production: 20 LPM) vortex‐based HC devices with other conventional devices, i.e., high‐pressure homogenizers and Venturi‐ and orifice‐based HC devices.…”

Oxidation of Sulphur pollutants in model and real fuels using hydrodynamic cavitation

“…This suggested the suitability of vortex-based devices for additive based HC-ODS. The influence of vortex based devices in liquid–liquid systems has been discussed in recent publications by Thaker and Ranade, showing that vortex-based cavitation devices have been effective for reducing the droplet diameter in a single pass through the device [35] , [36] , [37] . Applying this in ODS, vortex-based devices may effectively improve the fineness of the fuel emulsion increasing the interfacial area and improving oxidation.…”

“…Droplet sizes were not measured for the liquid–liquid systems considered in this work. However, these measurements have been carried out for oil in water emulsions by Thaker and Ranade [37] . This study clearly demonstrates that hydrodynamic cavitation generates droplets smaller than 10 µm and therefore greatly enhances liquid–liquid interfacial area.…”