Prediction of High Viscosity Liquid/Gas Two-Phase Slug Length in Horizontal and Slightly Inclined Pipelines

The production and transportation of high viscosity liquid/gas two-phase along petroleum production system is a challenging operation due to the lack of understanding the flow behavior and characteristics. In particular, accurate prediction of two-phase slug length in pipes is crucial to efficiently operate and safely design oil well and separation facilities. The objective of this study is to develop a mechanistic model to predict high viscosity liquid slug length in pipelines and to optimize the proper set of closure relationships required to ensure high accuracy prediction. A large high viscosity liquid slug length database is collected and presented in this study, against which the proposed model is validated and compared with other models. A mechanistic slug length model is derived based on the first principles of mass and momentum balances over a two-phase slug unit, which requires a set of closure relationships of other slug characteristics. To select the proper set of closure relationships, a numerical optimization is carried out using a large slug length dataset to minimize the prediction error. Thousands of combinations of various slug flow closure relationships were evaluated to identify the most appropriate relationships for the proposed slug length model under high viscosity slug length condition. Results show that the proposed slug length mechanistic model is applicable for a wide range of liquid viscosities and is sensitive to the selected closure relationships. Results revealed that the optimum closure relationships combination is Archibong-Eso et al. (2018) for slug frequency, Malnes (1983) for slug liquid holdup, Jeyachandra et al. (2012) for drift velocity, and Nicklin et al. (1962) for the distribution coefficient. Using the above set of closure relationships, model validation yields 37.8% absolute average percent error, outperforming all existing slug length models.

A Choking Model With Thermal Non-Equilibrium for Initially Subcooled Water

Mechanical non-homogeneous and thermal non-equilibrium phenomenon exists in two-phase critical flow compared with single phase flow. A one-dimensional two-fluid critical flow model is developed for initially subcooled water flowing in pipe or orifices. The model accounts for thermal nonequilibrium between the liquid and vapor bubbles and for interphase relative motion. In this model, an improved correlation to calculate flashing inception location and surperheat is proposed. The model consists of six conservation equations as well as a seventh equation representing bubble growth in bubbly flow. Closure of the set of governing equations is performed with constitutive relationships which determine the interfacial momentum terms due to mass exchange, wall to liquid and wall to vapour frictional forces, liquid to gas interfacial force and interfacial heat transfer rate. The model considers the development of three flow regimes, namely, bubbly, churn and annular flow regimes. Model predictions compare favorably with experimental data over a wide range of pressures and pipe diameters and lengths.

Connectivity, migration and recruitment in a catadromous fish

Understanding the influence of river hydrology and connectivity on the migration and recruitment of diadromous fishes is fundamental for species management and conservation. We investigated the downstream catadromous spawning migration of adult female congolli (Pseudaphritis urvillii) using acoustic telemetry, and subsequent juvenile recruitment, in the lower reaches of the River Murray, Australia, in 2009–2011. The years 2009 and 2010 were characterised by diminished freshwater flow, closure of tidal barrages, and disconnection of freshwater and estuarine habitats; however, a navigation lock was operated to facilitate downstream fish passage in 2010. In both years, >70% of individuals tagged upstream undertook downstream migrations, in association with day-of-the-year (June–July) and moonphase (full), and accumulated upstream of the tidal barrages. In 2009, fish were unable to pass the barrages and remained upstream, but in 2010, an estimated >15000 individuals passed through the navigation lock, including 40% of individuals tagged upstream. These transitioned rapidly (<24h) through the estuary and into the ocean. In association, abundances of upstream migrant juveniles in spring–summer 2010–2011 were up to 180 times greater than in spring–summer 2009–2010. Our study illustrates the potential impact of tidal barriers on migrations and population dynamics of catadromous fish, and the importance of understanding species-specific migration ecology.

Acute procedural outcomes of orbital atherectomy for the treatment of common femoral artery disease: Sub-analysis of the CONFIRM Registries

This analysis compared the angiographic outcomes of patients treated with orbital atherectomy for calcified common femoral artery (CFA) and superficial femoral artery (SFA) disease. The ideal revascularization strategy for CFA disease is unknown. Endarterectomy has been considered the standard of care for CFA disease for over 50 years. Endovascular intervention is becoming more commonly used to revascularize the CFA given the advances in technology and the less invasive nature of the procedure. Patient demographics, lesion characteristics, and procedure data for all CONFIRM patients with at least one CFA lesion location ( n=147 patients; n=200 lesions) were compared to patients with at least one SFA lesion location ( n=1508 patients; n=2367 lesions). The primary endpoint was angiographic complication, defined as the composite of dissection, perforation, slow flow, closure, spasm, embolism, or thrombosis. The CFA group had more patients with Rutherford class 4 and shorter lesion length. The CFA group had a higher final residual stenosis, shorter total run time, and shorter total inflation time. The primary endpoint was lower in the CFA group compared with the SFA group (17% vs 24%, p=0.02), driven by a lower dissection rate (10% vs 15%, p=0.04). Plaque modification of the CFA with orbital atherectomy was safe and compared favorably with SFA disease. The need for bail-out stenting was low. A randomized trial is needed to determine the ideal treatment strategy for calcified CFA disease.

Contemporary Dynamics in Rwandan Dances: Identity, Changing Creativity and the Globalisation of Affect

In contemporary Rwandan society, a revitalisation of ‘traditional’ dances can be observed which manifests in the proliferation of youth dance troupes, especially in urban areas. This revival is part of the drive, which has characterised Rwanda, to reconstruct itself after the traumatic 1994 genocide and to create a new, unified nation that strives to be ‘modern’ and integrated into the global market economy. This article explores the repertoire and dynamics of current Rwandan dance performances as they embody the new national identity, pointing to differences between the practices and views of dancers trained in the pre-genocide period and dancers from contemporary youth troupes. In this respect, two divergent views of creativity, found among these two categories of dancers, are distinguished: a perspective that privileges improvisation as a key creative process, on the one hand, and a view of creativity as innovation and the realisation of novel, pre-designed forms, on the other. With regard to the affective power of these performances, the article advances that contemporary dance shows generate affect, as bodily intensity, among the onlookers captured by the flow of spectacular, homogeneously performed dance forms. While evocative of Rwanda's new national identity, the latter neutralise connections with the dancers' subjective history and erase the dances' sociocultural background. In a final note, the changing dynamics in Rwandan dances are linked beyond this specific case study to the flow-closure dialectic of globalisation. It is suggested that dance's dual nature of both rhythmic flow and visual form is what makes it such a privileged marker of identity in our uncertain and violence-generating global times.