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

Lead Research Organisation: Imperial College London
Department Name: Department of Chemical Engineering

Abstract

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.

Publications

10 25 50
 
Description The work carried out as part of this project aimed at achieving fundamental understanding and providing accurate, reliable and robust modelling predictions of downward annular flows that have a tremendous impact on the design of such units as down-flow condensers and gas-liquid chemical reactors. The initial objectives of this proposal were very ambitious: resolving the coupling between the turbulent gas flow and the film through the shear stress in the interfacial region, and being able to model these interactions accurately without resorting to often unreliable closure relations or correlations is of considerable importance. This relied on a seamless connection between all workpackages. The experimental objectives associated with resolving the flow field using Particle Image Velocimetry (PIV) measurements in a thin film of thickness less than 1 mm were particularly challenging. We evaluated the ability of PIV to measure in thin liquid films and we successfully obtained demonstration measurements. We quantified the liquid film thickness in downward annular flows for different operating conditions and the associated temporal development around the circular duct. In this way, we quantified the spatial development of the instabilities as a function of distance along the duct and the correlation of the liquid film thickness between different locations around and along the duct. We then performed time-resolved PIV measurements of velocity around an interface of two liquids, formed by a central liquid jet surrounded by an annular flow of another liquid with different density, while we could maintain the same refractive index across the interface of the two liquids. The work quantified the different regimes of the instabilities in the axisymmetric annular geometry. It assisted in the understanding of the mechanisms that are responsible for the growth of instabilities at the interface and suggested appropriate scaling. In the other workpackages, we have managed to develop a single-phase DNS code and a preliminary version of a two-phase code (LES used for turbulent gas phase overlying laminar thin liquid film); this is in the process of being validated. We have also been successful in advancing the field in the fundamentals of interfacial flows at relatively small flow rates driven by a combination of gravitational forcing and gas shear. Future research will focus on the application of the time resolved PIV setup to fully resolve the flow field in the thin film in the presence of complex interfacial waves, the validation of the LES two-phase code, and the 'distillation' of closure relations for interfacial stress and velocity for the small-flow rate models.
Exploitation Route This research will underpin the improvement of the design of process equipment for which two-phase flows, and downwards annular flows, in particular, are of central importance. This includes the design of so-called 'falling film reactors', which actually involve not just falling films, but films that are driven by both gravity and gas shear from the downwards-flowing gas in the core of a circular duct. Further experimental, theoretical, modelling and simulation research is required before the fundamentals of these complex flows are understood fully. Also, further work will be required to develop understanding of these complex flows in the presence of heat and transfer, and chemical reactions. At that point, it will be possible define operating envelopes for the optimisation of the abovementioned process equipment that will maximise product yield and quality, minimise waste, emissions, and the carbon foot print associated with the process. Companies such as Procter & Gamble, who partially supported this work, are continuing to support our research along the direction indicated here. Potential beneficiaries include the home and personal care industry, the oil industry and the chemical industry. Achieving fundamental understanding and providing accurate, reliable and robust modelling predictions of these flows will have a tremendous impact on the design of such units as down-flow condensers and gas-liquid chemical reactors. This interest from industry has been demonstrated directly by the fact that Imperial College London has been commissioned by a multinational company, Proctor & Gamble (P&G), to carry out plant-specific work in this area. P&G has also contributed 10K per annum and 15K per annum in cash and in-kind support to this research. Furthermore, achieving understanding of the coupling between the turbulent gas flow and the film through the shear stress in the interfacial region, and being able to model these interactions accurately without resorting to often unreliable closure relations or correlations is of considerable importance. This is a generic problem which occurs often in multiphase flows and such interactions between a turbulent flow field and a wavy film abound in a wide class of industrially important flows from hydrocarbon transportation to cleaning of process equipment. The results of our work will be readily transferable to such flows.
Sectors Chemicals,Energy

 
Description The fundamental understanding of thin films driven by turbulent flows achieved through this grant has been used to work with companies like P&G on improving the efficiency of falling film reactors which are the engines of surfactant production (core to the business).
First Year Of Impact 2011
Sector Chemicals,Education,Energy,Environment,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description Feasibility study on reaction kinetics
Amount £40,000 (GBP)
Organisation Procter & Gamble 
Sector Private
Country United States
Start 01/2012 
End 01/2013
 
Description Surfactant effects on vertical gas-liquid flows
Amount £146,000 (GBP)
Organisation Shell Global Solutions International BV 
Department Shell Global Solutions UK
Sector Private
Country Netherlands
Start 09/2014 
End 09/2016
 
Title TMF database 
Description Database for multiphase flow data (e.g. flow regimes and their transitions for various flows as a function of system parameters). The data are collected as part of the TMF consortium, which compromises 14 oil-and-gas companies and design and software houses, led by Omar Matar. 
Type Of Material Database/Collection of data 
Provided To Others? Yes  
Impact TMF sponsors have access to the database and they have used it to improve their understanding of multiphase flows, which improves their design capabilities. The software houses that sponsor TMF use the data to validate the predictions of their codes. 
 
Description Strategic partnership with Procter and Gamble 
Organisation Procter & Gamble
Country United States 
Sector Private 
PI Contribution Engaged with P&G researchers to provide solutions to problems in the area of multiphase flows.
Collaborator Contribution Engaged with the research group to provide a constant source of good problems to work on, secondment opportunities for our researchers, and cash contribution.
Impact Procter and Gamble have provided £100000 cash contribution which was instrumental in our winning an EPSRC Programme Grant.
Start Year 2012
 
Description Next generation predictive tools for multiphase flows (BHRG) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Type Of Presentation keynote/invited speaker
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presented the next-generation predictive tools produced by the MEMPHIS Programme Grant to industrialists in the oil-and-gas sector at the BHRG conference in Cannes, June 2013. There was a lot of discussion following the presentation about the potential use of the MEMPHIS codes in providing solutions to flow assurance problems in the oil-and-gas industry.

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Year(s) Of Engagement Activity 2013