There is an increasing emphasis on process intensification and development of compact, intensified reactors and separators in recent years. Significant efforts are being made to develop such intensified reactors and separators without any moving parts. Some of the recent research studies have proven that a liquid‐liquid extractor based on the Coanda effect and feedback oscillations exhibit excellent mixing and liquid‐liquid contacting. These fluidic oscillators can potentially be used for a variety of other multiphase reactions and systems demanding enhanced mixing and heat and mass transfer. In this work, we have computationally investigated flow, mixing, and heat transfer in fluidic oscillators based on the Coanda effect. Available information on flow and mixing in fluidic oscillators was critically reviewed and key gaps in the available knowledge with respect to the design and optimization of fluidic oscillators were identified. Computational flow models were developed to characterize key flow features like unsteady flows, secondary vortices, and internal recirculation over a range of Reynolds number (Re = 90–1538) for three different oscillator designs. Systematic numerical studies were carried out to quantify different flow regimes, oscillations, and the influence of key geometric parameters on flow, mixing, and heat transfer. Simulated results were critically analyzed and are presented in the form of dimensionless numbers. The approach and results presented in this work will provide useful insights and a systematic basis for extending the applications of the Coanda‐based feedback oscillatory devices for a wide range of engineering applications.

Crystallisation is an important separation unit operation accounting for nearly 90% of organic molecules in the pharmaceutical and fine chemical industries. Recently, continuous crystallisation was demonstrated to have several advantages over the conventional batch crystallisation in terms of improved product consistency, reduced labor costs/economic footprint and better process control. Continuous stirred tank crystallisers, however, are limited in mixing/ heat transfer capabilities and have issues like cyclical oscillations in product quality. Tubular crystallisers can mitigate these issues, however, suffer from issues related to particle settling and blockages. Fluidic oscillators with one or more feedback channels are gaining popularity in recent years due to the advent of microfluidics. Jet oscillations in fluidic oscillators were shown to consistently provide vigorous mixing and heat transfer above a critical Reynold's number. In the present study, the feasibility of the fluidic oscillator as a continuous crystalliser was evaluated to mitigate challenges faced by previous continuous crystallisation technology. A novel 'loop setup' was proposed for continuous crystallisation and was investigated using the seeded anti-solvent crystallisation of paracetamol in a methanol-water system. The effect of key operating conditions of residence time, supersaturation ratio, operational mode, fluidic device, device orientation and seed size were investigated. Throughout the study it was observed that the loop setup gave product particle size distributions consistent with enhanced mixing behavior.Further, it was demonstrated that the proposed continuous crystalliser was better in terms of scale up in comparison with batch crystallisers. The presented results and approach will be useful to develop fluidic oscillators as a useful platform for continuous crystallization.

Graphical abstract

A simple model is presented to extract the particle size distribution (PSD) from the chord length distribution measured using a focused beam reflectance measurement probe. The model can be implemented using simple spread sheeting tools and does not require the description of additional parameters as opposed to previous models. The model was validated for two systems consisting of spherical ceramic beads by comparing model predicted PSD against the PSD obtained through image analysis (IA). Then, the model was evaluated by considering various systems consisting of irregularly shaped particles (sand/zinc dust/plasma alumina). Model predictions accurately predicted the mean but over‐predicted the variance of the PSD in comparison with the PSD obtained from IA. However, overall, a reasonable agreement was observed. Finally, the model was shown to be accurate in predicting PSD in comparison with the measured PSD for systems of practical relevance such as for paracetamol and p‐aminophenol crystals. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4215–4228, 2016

Fluidic oscillators (FOs) are used in a variety of applications, including process control and process intensification. Despite the simple design and operation of FOs, the fluid dynamics of FOs exhibit rich complexities. The inherently unstable flow, jet oscillations, and resulting vortices influence mixing and other transport processes. In this work, we computationally investigated the fluid dynamics of a new design of a planar FO with backflow limbs. The design comprised of two symmetric backflow limbs leading to bistable flow. The unsteady flow dynamics, internal recirculation, jet oscillations, secondary flow vortices were computationally studied over a range of inlet Reynolds numbers (2400-12,000). The nature and frequency of the jet oscillations were quantified. The computed jet oscillation frequency was compared with the experimentally measured (using imaging techniques) jet oscillation frequency. The flow model was then used to quantitatively understand mixing, heat transfer, and residence time distribution. The approach and the results presented in this work will provide a basis for designing FO's with desired flow and transport characteristics for various engineering applications.