Two-phase flow boiling in small to micro-diameter tubes

This thesis is dedicated to the experimental and theoretical study of flow boiling in small to micro diameter tubes using R 134a. Flow pattern, heat transfer and pressure drop studies were conducted in stainless steel cold drawn tubes with internal diameter 2.88,1.1, and 0.52 mm using an existing facility that was designed with a long term research objective of improving the fundamental understanding of flow boiling in small metallic tubes. The facility was moved to the present location from London South Bank University and re-commissioned before carrying out the experiments. The test sections were heated by a direct passage of alternating current and wall temperatures were measured at 15 axial locations by miniature thermocouples that were directly spotwelded at the tube outer wall. A digital high-speed camera was used to simultaneously observe the flow patterns (during the heat transfer tests) directly at a borosilicate glass tube located immediately downstream of the heat transfer test section. The purpose of the flow visualization study was to support understanding of the heat transfer characteristics and development of flow regime-specific models. The heat transfer and pressure drop data of X. Huo (2005) in the 4.26 and 2.01 mm tubes and the flow visualization results of Chen (2006) for the tubes of diameter 4.26,2.88,2.01, and 1.1 mm were included with the new data in an extensive analysis of flow boiling heat transfer and pressure drop in five vertical tubes with internal diameters 4.26, 2.88,2.01, 1.1 and 0.52 mm. The wide range of tube diameter was chosen to investigate the influence of tube size and possibly identify the threshold where the effect of small or micro diameter effects become significant. In the experiments, parameters were varied in the ranges: mass flux 100 to 700 kg/m2s; heat flux 1.6 to 150 kW/m; pressure 6 to 14 bar; quality up to 0.9 and the inlet temperature was controlled at a subcooling of 1-5K. There was no clear significant difference between the characteristics and magnitude of the heat transfer coefficients in the 4.26 mm and 2.88 mm tubes but the coefficients in the 2.01 and 1.1 mm tube were higher. The heat transfer results suggested that a tube size of about 2 mm might be considered as a critical diameter to distinguish small and conventional tubes. Further differences have now been observed in the 0.52 mm tube. These differences, both in flow patterns and heat transfer, indicate a possible second change from small to micro behaviour at diameters less than 1 mm for R 134a. Also, the results showed axial variations in heat transfer characteristics marking the importance of surface conditions on heat transfer. This calls for a further detail investigation to understand the underlying physics in the initiation of boiling, effect of surface condition on nucleation, and structure of newly emerging flow patterns, particularly in very small tubes. Existing correlations were examined using the results of the five tubes and indicated that these correlations do not predict the present small diameter data to a satisfactory degree. Therefore, two new correlations that take into account both magnitude and characteristic effect of tube diameter have been proposed covering the 4.26 mm-1.1 mm and the smallest 0.52 mm tube, respectively. A detailed comparison was also made with the state-of-the-art flow regime-specific model of Thome et al. (2004) and verified that the mechanistic modelling approach has a promising capability of predicting two phase heat transfer in small diameter tubes, although it still requires further development. Some improvements have been proposed and tested against the current data. Using a similar approach, a new two phase pressure drop model has been proposed and compared with the current data with encouraging results.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Numerical investigation of saturated flow boiling on thin walls

Boiling heat transfer provides a means of removing high heat fluxes at low temperature differences in many applications in the power and process industries. A strong interest has been also developed for the cooling of silicon-based devices, such as electronic chips. However, a complete model to describe the processes involved has not been developed as yet. This PhD project focused on the study of nucleate pool boiling via numerical simulations for a solid plate horizontally immersed in a saturated liquid with a large number of potential nucleation sites. The simulations were developed by a FORTRAN code based on a hybrid approach, combining the 3-dimensional time-dependent solution for the temperature field on the substrate with semi-empirical models for phenomena occurring on the liquid side. The starting point of the project was the modification of a previous version of the code in order to reduce the computational time (in collaboration with Dr. Nelson at Los Alamos National Laboratory) and improve the modelling of the physics of the processes. One of the key features of the code is the flexibility in adapting to different conditions. In fact the code was used to study bubble growth, site activation frequency and superheat variations, as well as the interactions between nucleation sites. The differences in behaviour between very thin metal foils immersed in water and thicker silicon substrates in FC-72 were studied. The results were compared with experimental results produced at the University of Edinburgh and the University of Ljubljana, both partners of this project. Both the numerical and physical modifications introduced made it possible to have simulations for a large number of sites, of the order of 100, in reasonable times, of the order of days, so that the code can be now used as a tool for the design of new test sections.EThOS - Electronic Theses Online ServiceEngineering and Physical Sciences Research Council (EPSRC) grant EP/C532805/1GBUnited Kingdo

Combined effect of electric field and surface modification on pool boiling of R-123

The effect of surface modification and high intensity electric field (uniform and non – uniform) acting separately or in combination on pool boiling of R-123 is presented in this thesis. The effect of surface modification was investigated on saturated pool boiling of R-123 for five horizontal copper surfaces modified by different treatments, namely: an emery polished surface, a fine sandblasted surface, a rough sandblasted surface, an electron beam (EB) enhanced surface and a sintered surface. Each 40 mm diameter heating surface formed the upper face of an oxygen-free copper block, electrically heated by embedded cartridge heaters. The experiments were performed from the convective heat transfer regime to the critical heat flux, with both increasing and decreasing heat flux, at 1.01 bar, and additionally at 2 bar and 4 bar for the emery polished surface. Significant enhancement of heat transfer with increasing surface modification was demonstrated, particularly for the EB enhanced and sintered surfaces. The emery polished and sandblasted surface results are compared with nucleate boiling correlations and other published data. The effect of uniform and non-uniform electric fields on saturated pool boiling of R-123 at 1.01 bar pressure was also examined. This method of heat transfer enhancement is known as electrohydrodynamic abbreviated as EHD-enhancement. A high voltage potential was applied at the electrode located above the heating surface, which was earthed. The voltage was varied from 0 to 30 kV. The uniform electric field was provided through a 40 mm diameter circular electrode of stainless steel 304 wire mesh having an aperture of 5.1 mm, while the non-uniform electric field was obtained by using a 40 mm diameter circular rod electrode with rods 5 and 8 mm apart. The effect of uniform electric field was investigated using all five modified surfaces, i.e. emery polished, fine sandblasted, rough sandblasted, EB enhanced and sintered surfaces, while non – uniform electric field was tested using the emery polished, fine sandblasted, EB enhanced and sintered surfaces. The effect of pressure on EHD enhancement was also examined using emery polished surface at saturation pressure of 2 and 4 bars while the electric field was fix at 20 kV corresponding to 2 MV/m. Further, the bubble dynamics is presented for the emery polished surface obtained using a high-speed high – resolution camera.EThOS - Electronic Theses Online ServiceGovernment of PakistanGBUnited Kingdo

Combined effect of electric field and surface modification on pool boiling of R-123

The effect of surface modification and high intensity electric field (uniform and non – uniform) acting separately or in combination on pool boiling of R-123 is presented in this thesis. The effect of surface modification was investigated on saturated pool boiling of R-123 for five horizontal copper surfaces modified by different treatments, namely: an emery polished surface, a fine sandblasted surface, a rough sandblasted surface, an electron beam (EB) enhanced surface and a sintered surface. Each 40 mm diameter heating surface formed the upper face of an oxygen-free copper block, electrically heated by embedded cartridge heaters. The experiments were performed from the convective heat transfer regime to the critical heat flux, with both increasing and decreasing heat flux, at 1.01 bar, and additionally at 2 bar and 4 bar for the emery polished surface. Significant enhancement of heat transfer with increasing surface modification was demonstrated, particularly for the EB enhanced and sintered surfaces. The emery polished and sandblasted surface results are compared with nucleate boiling correlations and other published data. The effect of uniform and non-uniform electric fields on saturated pool boiling of R-123 at 1.01 bar pressure was also examined. This method of heat transfer enhancement is known as electrohydrodynamic abbreviated as EHD-enhancement. A high voltage potential was applied at the electrode located above the heating surface, which was earthed. The voltage was varied from 0 to 30 kV. The uniform electric field was provided through a 40 mm diameter circular electrode of stainless steel 304 wire mesh having an aperture of 5.1 mm, while the non-uniform electric field was obtained by using a 40 mm diameter circular rod electrode with rods 5 and 8 mm apart. The effect of uniform electric field was investigated using all five modified surfaces, i.e. emery polished, fine sandblasted, rough sandblasted, EB enhanced and sintered surfaces, while non – uniform electric field was tested using the emery polished, fine sandblasted, EB enhanced and sintered surfaces. The effect of pressure on EHD enhancement was also examined using emery polished surface at saturation pressure of 2 and 4 bars while the electric field was fix at 20 kV corresponding to 2 MV/m. Further, the bubble dynamics is presented for the emery polished surface obtained using a high-speed high – resolution camera.EThOS - Electronic Theses Online ServiceGovernment of PakistanGBUnited Kingdo

Supporting people with type 2 diabetes in effective use of their medicine through mobile health technology integrated with clinical care (SuMMiT-D Feasibility): a randomised feasibility trial protocol

INTRODUCTION: Type 2 diabetes is common, affecting over 400 million people worldwide. Risk of serious complications can be reduced through use of effective treatments and active self-management. However, people are often concerned about starting new medicines and face difficulties in taking them regularly. Use of brief messages to provide education and support self-management, delivered through mobile phone-based text messages, can be an effective tool for some long-term conditions. We have developed messages aiming to support patients' self-management of type 2 diabetes in the use of medications and other aspects of self-management, underpinned by theory and evidence. The aim of this trial is to determine the feasibility of a large-scale clinical trial to test the effectiveness and cost-effectiveness of the intervention, compared with usual care. METHODS AND ANALYSIS: The feasibility trial will be a multicentre individually randomised, controlled trial in primary care recruiting adults (≥35 years) with type 2 diabetes in England. Consenting participants will be randomised to receive short text messages three times a week with messages designed to produce change in medication adherence or non-health-related messages for 6 months. The aims are to test recruitment methods, retention to the study, the feasibility of data collection and the mobile phone and web-based processes of a proposed definitive trial and to refine the text messaging intervention. The primary outcome is the rate of recruitment to randomisation of participants to the trial. Data, including patient reported measures, will be collected online at baseline and the end of the 6-month follow-up period. With 200 participants (100 in each group), this trial is powered to estimate 80% follow-up within 95% CIs of 73.8% to 85.3%. The analysis will follow a prespecified plan. ETHICS AND DISSEMINATION: Ethics approval was obtained from the West of Scotland Research Ethics Committee 05. The results will be disseminated through conference presentations, peer-reviewed journals and will be published on the trial website: www.summit-d.org (SuMMiT-D (SUpport through Mobile Messaging and digital health Technology for Diabetes)). TRIAL REGISTRATION NUMBER: ISRCTN13404264

Neuromarketing and consumer neuroscience:contributions to neurology

Background: 'Neuromarketing' is a term that has often been used in the media in recent years. These public discussions have generally centered around potential ethical aspects and the public fear of negative consequences for society in general, and consumers in particular. However, positive contributions to the scientific discourse from developing a biological model that tries to explain context-situated human behavior such as consumption have often been neglected. We argue for a differentiated terminology, naming commercial applications of neuroscientific methods 'neuromarketing' and scientific ones 'consumer neuroscience'. While marketing scholars have eagerly integrated neuroscientific evidence into their theoretical framework, neurology has only recently started to draw its attention to the results of consumer neuroscience.Discussion: In this paper we address key research topics of consumer neuroscience that we think are of interest for neurologists; namely the reward system, trust and ethical issues. We argue that there are overlapping research topics in neurology and consumer neuroscience where both sides can profit from collaboration. Further, neurologists joining the public discussion of ethical issues surrounding neuromarketing and consumer neuroscience could contribute standards and experience gained in clinical research.Summary: We identify the following areas where consumer neuroscience could contribute to the field of neurology:. First, studies using game paradigms could help to gain further insights into the underlying pathophysiology of pathological gambling in Parkinson's disease, frontotemporal dementia, epilepsy, and Huntington's disease.Second, we identify compulsive buying as a common interest in neurology and consumer neuroscience. Paradigms commonly used in consumer neuroscience could be applied to patients suffering from Parkinson's disease and frontotemporal dementia to advance knowledge of this important behavioral symptom.Third, trust research in the medical context lacks empirical behavioral and neuroscientific evidence. Neurologists entering this field of research could profit from the extensive knowledge of the biological foundation of trust that scientists in economically-orientated neurosciences have gained.Fourth, neurologists could contribute significantly to the ethical debate about invasive methods in neuromarketing and consumer neuroscience. Further, neurologists should investigate biological and behavioral reactions of neurological patients to marketing and advertising measures, as they could show special consumer vulnerability and be subject to target marketing

The Effect of Complex Interventions on Depression and Anxiety in Chronic Obstructive Pulmonary Disease: Systematic Review and Meta-Analysis

Background Depression and anxiety are very common in people with chronic obstructive pulmonary disease (COPD) and are associated with excess morbidity and mortality. Patients prefer non-drug treatments and clinical guidelines promote non-pharmacological interventions as first line therapy for depression and anxiety in people with long term conditions. However the comparative effectiveness of psychological and lifestyle interventions among COPD patients is not known. We assessed whether complex psychological and/or lifestyle interventions are effective in reducing symptoms of anxiety and depression in patients with COPD. We then determined what types of psychological and lifestyle interventions are most effective. Methods and Findings Systematic review of randomised controlled trials of psychological and/or lifestyle interventions for adults with COPD that measured symptoms of depression and/or anxiety. CENTRAL, Medline, Embase, PsychINFO, CINAHL, ISI Web of Science and Scopus were searched up to April 2012. Meta-analyses using random effects models were undertaken to estimate the average effect of interventions on depression and anxiety. Thirty independent comparisons from 29 randomised controlled trials (n = 2063) were included in the meta-analysis. Overall, psychological and/or lifestyle interventions were associated with small reductions in symptoms of depression (standardised mean difference −0.28, 95% confidence interval −0.41 to −0.14) and anxiety (standardised mean difference −0.23, 95% confidence interval −0.38 to −0.09). Multi-component exercise training was the only intervention subgroup associated with significant treatment effects for depression (standardised mean difference −0.47, 95% confidence interval −0.66 to −0.28), and for anxiety (standardised mean difference −0.45, 95% confidence interval −0.71 to −0.18). Conclusions Complex psychological and/or lifestyle interventions that include an exercise component significantly improve symptoms of depression and anxiety in people with COPD. Furthermore, multi-component exercise training effectively reduces symptoms of anxiety and depression in all people with COPD regardless of severity of depression or anxiety, highlighting the importance of promoting physical activity in this population

Mixing in multiphase jet flow

A series of experiments has been conducted for comparison with the results of a computer code called CHYMES. It is intended to calculate the coarse mixing of molten metal with water by solving the equations of the Separated Flow Model. These are derived by volume averaging and the terms that relate them to the particular case of participate flow are discussed. An experimental apparatus that is compatible with CHYMES and coarse mixing has been constructed which projects a jet of ball bearings into a thin tank of water. Experiments over a wide range of conditions were conducted at room temperature. Owing to practical difficulties only one, poorly controlled experiment with hot ball bearings was performed. Under nearly all sets of conditions an arrow-shaped plume was obtained. The speed of penetration of the plume varied little with changes in experimental conditions. The width of the plume was most strongly influenced by the widths of the tank and the jet. The individual paths of some particles were followed; it appeared that their motion was mostly dependent on their position in the plume. A model of the plume is proposed, based upon its front being impermeable to water in the vertical direction. Much of the detail of the experimental plumes was not present in the computational results and they responded differently to changes in conditions. It is proposed that this is a result of the different forms of the two sets of plumes. To rectify this an experimental plume was volume averaged. A method to determine a suitable averaging volume size is described. The process results in a plume similar to the computational ones. The length scales required for volume averaging to be successful are discussed and the possibility that this method is inappropriate for describing coarse mixing is admitted.</p