Particle Dynamics in Turbulent Reactive Flows: A Unified Formulation

Lead Research Organisation: University of Manchester
Department Name: Mechanical Aerospace and Civil Eng

Abstract

The aims of this research are: to formulate a comprehensive, unified approach for modelling turbulent reactive flows with particle dynamics, and to develop efficient numerical methods and computational tools for its implementation. The research will thus seek the unification of two major scientific fields that have so far been developed independent of each other, namely turbulence modelling and population balance, within the framework of transported probability density function (PDF) approaches, which are a general class of methods for the description of stochastic processes. The new approach will be of direct relevance to two major practical problems: the reduction of harmful emissions of particulates from reciprocating and rotating engines and the tailor-made synthesis of advanced materials composed of nanoparticles.
 
Description A novel framework for modelling turbulent reactive flows with particle formation has been developed during this project. This framework unifies methods and models employed in the fields of turbulence modelling and population balance equation (PBE) modelling of particulate systems. It is based on the concept of transported probability density function (PDF) approaches, which are a general class of methods for the description of stochastic processes.

Particulate systems are described by a particle size distribution (PSD) or a distribution of some other characteristic property. This distribution is of vital importance, as it characterises the physical properties of the particulate system. If it is a commercial product, the PSD determines its suitability for particular applications, and therefore the ability to predict and control it enables us to tailor the product to particular applications. If the particles are an important process intermediate, then the PSD plays an important role in the outcome of the process.

The main problem that we have addressed in this project is the prediction of the PSD in systems with turbulent flow. The majority of practical, engineering applications involving particulates feature turbulent flow. We have shown that the interaction of turbulence with particle formation gives rise to unclosed terms in the Reynolds-averaged PBE.

The main point of the new approach is the derivation of the transported PBE-PDF equation, an equation that describes particulate systems in turbulent flow fields and overcomes the closure problems relating to the interaction of turbulence with particle formation and coagulation. Solution of this equation yields information about the distribution of the PSD in space, as well as predicting the entire distribution (rather than just the moments of it, as is the case with most conventional approaches). In addition, we developed an efficient practical method for solving this equation: a Lagrangian Monte-Carlo method that couples the PBE-PDF equation with computational fluid dynamics (CFD).

The approach has been applied to two problems. The first one is precipitation in a turbulent reactor, a process of particular importance in the pharmaceutical industry. The second problem is aerosol formation in a turbulent jet, a problem relevant to environmental science. In both cases, it was demonstrated via comparisons with existing experimental data that the new method is capable of producing very good predictions of the particle size distribution within a reasonable amount of CPU time. In addition, the results of the approach enabled an in-depth analysis of the mechanisms of interaction of turbulence and particle formation and drawing insight into the experiments studied.

The framework developed here is relevant to a wide class of problems. We could mention the following areas of potential extension and application of this research:

The production of advanced materials comprised of ultrafine particles, such as silica, titania and nanocomposite ceramic powders. The commercial value of these products can be maximized by the ability to control the PSD.

Pharmaceutical applications, such as the production of drugs via crystallisation or reactive precipitation and the formation of nanoparticles intended for drug delivery.

The analysis of spray combustion in engines.

The reduction and control of soot emissions from diesel engines and gas turbines and the mitigation of emission of atmospheric aerosols from industrial plumes.
Exploitation Route The developments made in this project will lead to the improved formulation of problems in this field and to the development of efficient approaches for their solution via engineering software, both within academia and the particle technology industry.
Sectors Chemicals,Energy,Environment,Pharmaceuticals and Medical Biotechnology
 
Description This reseasrch project has developed a new framework for modelling turbulent reacting flows with polydispersed particle formation. This has in turn led to development of numerical approaches and of computer software implementing them. These approaches have found application to industrial problems involving polydispersed particles in turbulent flows, particularly in the particle technology industry.
Sector Chemicals,Energy,Manufacturing, including Industrial Biotechology
Impact Types Economic