Advanced experimental and numerical methods for te prediction of complex gas liquid annular flows

The proposed work involves an experimental and modelling investigation of vertically downwards gas-liquid annular flows. These are the key components in a wide variety of industrial applications, prime examples of which are, condensers and chemical reactors used in the production of detergents. In the latter case, a liquid feedstock is injected as a film onto the inside of a bundle of tubes and undergoes an exothermic sulphonation by contact with air containing SO3 which flows down the tubes co-currently with the films on the tube walls. To obtain the required quality of the product, the temperature of the reacting liquid must be rigidly controlled; otherwise, undesirable by-products are formed. Industry has made good progress in modelling these systems but such modelling is limited by the complexity of the underlying physics. First, a complex pattern of waves is formed on the interface and these affect the interaction between the gas and liquid and also the reaction and heat transfer processes. Secondly, liquid droplets are torn off the film and react with the SO3 in the gas in an uncontrolled way. Knowing which flow regime occurs under which conditions, and being able to predict the flow regimes in a systematic manner is crucial for the efficient and optimal operation of reactors that exploit downwards annular gas-liquid flows. Whereas vertically upwards annular flows have received considerable attention in the literature (see e.g. the work of Hewitt and Hall Taylor1a, Hewitt1b, Hewitt and Govan1c and Barbosa et al.1d), there has been very little work on vertically downwards annular flows. This is surprising given the early studies of Webb and Hewitt1e, whose work in this area has shown that the interactions between the turbulent gas core and the thin liquid film, particularly when both gravity and interfacial shear are significant, give rise to many complex phenomena and rich dynamics, which are not well-understood. The current state of modelling of downwards annular flows in general is insufficient. Hence, there is a need for a substantially improved understanding of the coupling between the liquid film and gas turbulence through the interfacial stress exerted by the gas onto the liquid which is responsible for wave formation and drop entrainment; achieving such an understanding is the aim of the proposed work. The project proposed here is a well-balanced synergistic approach adopting recent, advanced experimental methods, results of the detailed numerical and analytical studies conducted in other EPSRC-funded projects, EP/D031222 and EP/E021468, unavailable at the time of earlier studies, and advanced theoretical and modelling methodologies to develop efficient and accurate methods for the systematic prediction of flow interfacial behaviour and flow regimes in downwards annular flows.