Free and Confined Buoyant Flows

Flows driven by density differences, whether natural or induced by man, surround us on a wide range of scales. As a density difference is generated by commonly occuring temperature or salinity differences, these flows are ubiquitous. On the largest scales, they transport and mix the water in our oceans and air in our atmosphere. At an intermediate scale, frequently referred to as the mesoscale, the cold outflows which flow downwards from thunderstorms and impact the ground are a common aviation hazard. On a smaller scale, the toxins emitted by fire plumes or dense gas releases are a threat to health. This work focusses on a continuous, localised release of buoyant fluid from a horizontal source whose dimension is significantly smaller than the horizontal and vertical scales of the quiescent, uniform environment into which the flow propagates. We consider both passive releases, which are only driven by the density difference between the source fluid and the denser ambient, and forced releases, where the fluid has source momentum in addition to its buoyancy. In general, these releases give rise to turbulent plumes, a familiar example being the cloud of smoke and water vapour seen rising from a chimney stack on a cold, still morning. The first part of the research presented in this thesis focusses on the freely-propagating plume. Velocity and temperature measurements are presented which contribute considerably to the existing experimental data available in the literature. This data-set is used to validate classical plume theory and make a check of the experimental set-up so that the subsequent results can be presented with confidence. It is also possible that this dataset will be used by other researchers to validate numerical simulations of buoyant flows. The effect of varying the source balance of buoyancy and momentum upon the plume dynamics is investigated. Measurements also reveal the development region or ‘zone of flow establishment’. Frequently, plumes are restricted by some form of confinement, either vertically, horizontally or both, for example the plumes rising from the occupants of a room. Whether this restriction takes the form of a solid wall, free surface or density discontinuity, the disturbance to the flow is typically significant. The simplest confining boundary is arguably a horizontal surface located some distance H from the source of buoyant fluid. The horizontal boundary forces the vertical flow to change direction and propagate radially outwards. This type of semi-confined flow can be frequently observed in the natural world with examples including the impingement of a fire plume against a ceiling and a plume of volcanic ash with the tropopause. An investigation into this type of flow, which we refer to as the ‘impinging buoyant plume’, constitutes the second part of the research. Plume impingement has not been studied as extensively as jet impingement and several key questions remain unanswered. For example, how much energy is lost as the vertical flow is forced to turn and propagate horizontally? What effect does buoyancy have on the horizontal flow? How does the flow evolve with increasing radial distance and what is the effect of changing the source-boundary separation? These are just some of the questions addressed in this thesis guided by the novel application of highly-resolved Particle Image Velocimetry measurements to this relatively low-speed, buoyant, turbulent flow. The free and impinging plume studies both employed similar experimental techniques and analysis methods. Statistics of the steady flow were determined from a highly-resolved data-set. The third part of the research concerns a time-dependent flow and is of a more qualitative nature. The complexity of the impinging plume increases considerably when a radial confinement is added to the geometry. This restricts the radial propagation of the flow produced by the impinging plume. The plume is now effectively enclosed and buoyant fluid begins to accumulate within and thereby fill the enclosure, a configuration known as the ‘filling-box’. While previous work, which we shall go on to review in detail, has contributed analytical solutions for the density profiles in the enclosure after a certain time-scale has elapsed, in many applications, such as the spread of smoke carried by a fire plume in a room, what happens in the early moments of a confined release following impingement with the horizontal and then vertical boundaries, may be critical. This has been overlooked in earlier studies, yet is crucial as it is during these early transients that the fire is best tackled by fire-fighters. Visualisations and velocity measurements of these early filling-box transients are reported. This work provides the first detailed measurements of the velocity field induced in the filling-box by the turbulent plume during the early transients and resolves the turbulent structures that comprise the plume outflow. The experiments which investigated the impinging jet were conducted on thermal air plumes in facilities at the Laboratoire de Mécanique des fluides et de l’Acoustique (LMFA) of École Centrale de Lyon (ECL). Filling-box experiments were performed on brine plumes in fresh water in visualisation tanks in the Department of Civil & Environmental Engineering at Imperial College London (ICL). The set of experiments at ECL used a combination of Particle Image Velocimetry (PIV) and thermocouples to measure flow velocities and temperatures. At ICL, Light-Induced Fluorescence (LIF) enabled visualisation of a plane through the centre of the axisymmetric flow to complement the PIV work. These experiments enabled effective use of the equipment, techniques and expertise available at both institutions. The principal objective of this research was to use experimental measurements to answer questions of importance regarding these impinging flows which remain unresolved in the literature. Using experimental techniques unavailable to earlier researchers, the work presented herein makes a substantial contribution to the existing knowledge of these flows. Free and impinging plumes and the dynamics of the filling-box flow are studied in detail. Notably, the data gathered are of very high spatial resolution and provide a resource for those interested by not only the plume dynamics, but also radial gravity currents and the filling-box

Accounting and redistribution: The palace and mortuary cult in the Middle Kingdom, ancient Egypt

This paper examines detailed historical material drawn from primary sources to explore the role of accounting practices in the functioning of several key stages of the redistributive economy of the Middle Kingdom, ancient Egypt. First, the paper attends to the role of accounting in securing a regular flow of commodities to the state, in the form of taxation in kind. The historical material suggests clearly that accounting practices played a crucial role in levying and collecting precise tax liabilities, and in monitoring the storing of commodities in state granaries and storehouses. The second level of analysis is concerned with the role of accounting in coordinating the outflow of commodities to consumption units focusing on two examples. The first relates to the role of accounting in the distribution of food provisions to members of the Royal family and palace dependents while on a journey; the second examines the role of accounting in the writing and execution of a series of contracts to promote the mortuary cult of a dead individual. In both cases, the paper argues that the accounting practices were linked strongly to the social, political and economic contexts within which these accounting practices functioned

Towards an understanding of changing accounting practice using institutional theory: the case of the royal tobacco factory of Seville

This paper is initially informed byan institutional theoretical framework developed by Fligstein (1993) to analyse changes in accounting practices that took place in the Royal Tobacco Factory (RTF) of Seville during the period 1760-1790. Deploying the institutional theory framework, it is possible to argue that the significantly greater development and use of accounting practices during that period can be linked to the move to the much larger and more purpose-built new factories, the dec1ine in total tobacco consumption and the pressure to increase revenue for the Spanish Crown while redllcing prodllction cost and maintaining high product quality to deter entry. These new accollnting practices may have developed in part with the intent of improving factory efticiency. It is also arglled that these new accollnting practices provided enhanced external legitimacy for the RTF in the face of the events discussed aboye and cOllld have contributed to the long survival of de RTF as a monopolist. The paper, however, suggests that typologies such as the one developed by Fligstein are too restrictive in linking the emergence of specific organizational actions (e.g. accollnting practises) as a response to a particular organizational typology, in Fligstein's case a conception of control. The paper conc1udes by suggesting that it may be best to refrain from conceptllalizing the rise of accounting practices in terms of strict matching with other organizational parameters, such as strategy, structure, or mode of control

Control and cost accounting practices in the Spanish royal tobacco facfory

The aim of this paper is to analyse the cost accounting system implemented in 1773 by a large Spanish tobacco company which operated as a monopolist. Drawing on data extracted from original archives, the paper examines the characteristics of the cost system within the broader context of a strict control system. The paper argues that there was a connection between the two systems. One of the main roles of the cost accounting system was to buttress a set of structural measures instituted in the RTF with the aim of minimising the scope for tobacco theft. Another aim was to impart visibility upon the various activities undertaken in the RTF. The paper also examines the role of the cost accounting practices as a disciplinary regime. A combination of physical measures, reflecting the rates and mixes of resource utilisation and monetary measures were developed to facilitate monitoring and surveillance of the activities of the factory employees. These measures were used to establish a powerful regime of calculability which rendered human accountability visible. Such calculability created an environment at the RTF in which management could compare, differentiate, hierarchaise, homogenise, and even exclude individuals

Towards an institutional analysis of accounting change in the Royal Tobacco Factory of Seville

This paper is initially informed by an institutional sociological framework to analyze changes in accounting practices that took place in the Royal Tobacco Factory (RTF) of Seville during the period 1760-1790. We argue that the significantly greater development and use of accounting practices during that period can be linked to the move to the much larger and more purposefully built new factories, the decline in total tobacco consumption, and the pressure to increase revenue for the Spanish Crown while reducing production cost and maintaining high product quality to deter entry. These new accounting practices were developed in part with the intent of improving factory efficiency, but importantly, they enhanced the external legitimacy of the RTF in the face of the events mentioned above and contributed to the long survival of the RTF as a monopolist

Improving access to cognitive behavioural therapy groups for postnatal women following partnership work: a service evaluation

Objective: Postnatal depression (PND) can adversely impact the wellbeing of the mother and child. However, accessing mental health support is a challenge for the perinatal population. While most studies have focused on the effectiveness of stand-alone interventions in treating PND, recent studies have highlighted the need for collaboration and inter-agency working. This study evaluated the impact of partnership working on the effectiveness of cognitive behavioural therapy (CBT) groups for women with PND and anxiety in an Improving Access to Psychological Therapies (IAPT) service. Method: This study is a service evaluation conducted within a primary care setting. It compares engagement and outcomes from pre-partnership groups that were delivered before the development of local partnership working arrangements with post-partnership groups developed in collaboration with a secondary care perinatal mental health service (PNMHS). Participants attended either pre-partnership (N = 26) or post-partnership (N = 19) CBT groups. Results: Following developments in partnership working arrangements, the diversity and number of referrals to CBT groups significantly increased, with a 50% increase in self-referrals. Retention from referral to start of treatment was high, with an increase to 100% following partnership working arrangements (88.5% vs. 100%). Completion rates were also higher following partnership working arrangements (84.2% vs. 61.5%). However, these differences and differences in recovery outcomes did not reach statistical significance. Discussion: Overall this study has found promising results for the effectiveness of partnership working on perinatal care, particularly when improving access to mental health services for women with PND and anxiety

British research in accounting and finance (2001–2007): the 2008 research assessment exercise

No abstract available

The development of accounting regulations for foreign invested firms in China: The role of Chinese characteristics

Drawing on actor network theory (ANT), this paper analyses the role of Chinese characteristics in the emergence of three accounting regulations for foreign invested firms (FIFs) as part of China’s recent transformation to become part of the “world order”. The paper examines how international accounting standards (IAS) and existing Chinese accounting were translated into new regulations for FIFs, and how these translations were shaped by malleable interpretations of Chinese characteristics. Chinese characteristics were a discursive obligatory passage point (OPP) rendered malleable through cognition and the sanctions of political authority to suit the interests of actors seeking to produce new accounting regulations. Chinese characteristics were a signifier that carved out a space for local networks to attain their identity and retain some measure of independence from global networks, shaped the construction of each accounting regulation for FIFs into an attractive package, and influenced the adaptation and transformation of those elements of Western accounting that arrived into China. In turn, IAS became part of the discursive field on accounting regulation that helped mediate the shifts in the interpretation of Chinese characteristics over time

Military, ‘managers’ and hegemonies of management accounting controls: A critical realist interpretation

The paper brings to light the horizontal dimension of hegemony, i.e. the relationship between dominant social groups as they form a ‘power bloc’ and its significance for management accounting control (MAC) changes, drawing on an intensive case study of a public sector unit in Pakistan. The study finds that the political strategies of the two dominant social groups eventually led to a ‘conflicted compromise’, resulting in changes to the MACs in the case organisation. However, the ideologies of both groups were seriously compromised vis-à-vis the enacted MACs. This necessitated the use of coercive measures to compel the dominated groups, such as lower pay-grade employees and labour, to accept the changes. We argue that the use of coercive measures without ideological support resulted in a weak hegemonic arrangement at the level of the firm, with implications for possible resistance from the dominated groups and for the longevity of the MAC changes. The paper is informed by a critical realist interpretation of hegemony which helps improve our understanding of the role of the state in bringing about MAC changes. Based on our analysis, we argue that it would be useful not only to trace the economic compulsions of the state but also to examine the vested interests of powerful social groups engaged in hegemonic struggles within the state for better understanding of NPM-driven MAC changes in an SOE