Theoretical and physical modelling of the thermal performance of water wall systems

Water wall is an excellent passive solar strategy which can maintain thermal comfort in buildings while reducing energy consumption. Existing water wall studies are mainly based on simple heat balance models, in which convective heat transfer coefficients are assumed constant and radiation exchange is commonly neglected. Further, the application of the CFD approach to water wall research is very rare. These research gaps are addressed in this study through the development of a comprehensive transient heat balance model and unsteady CFD modelling. The thesis covers three major topics. Firstly, the turbulent natural convection with and without radiation transfer in two-dimensional and three-dimensional air-filled differentially heated cavities is numerically investigated using various RANS (Reynolds Averaged Navier-Stokes) turbulence models and the Discrete Ordinates radiation model. It is found that the shear-stress transport k-ω model has the best overall performance in terms of capturing the main features of the flow and predicting the time-averaged quantities. Secondly, a comprehensive conjugate conduction-convection-radiation model for transient analysis of a semi-transparent water wall system is developed. It is found that reducing the transmissivity of the Perspex or glass walls is the most effective, practical and economical way to improve the thermal performance of the semi-transparent water wall system. Finally, the thermal performance of an opaque water wall system is numerically investigated and compared against a conventional concrete wall system for the typical climate conditions in Sydney, Australia. The results indicate that less supplementary energy is required in winter than that in summer to maintain a comfortable interior temperature. Further, the water wall system performs significantly better than the concrete wall system of the same thickness in the winter climate of Sydney, whereas both systems have a similar performance in summer

International External Validation Study of the 2014 European Society of Cardiology Guidelines on Sudden Cardiac Death Prevention in Hypertrophic Cardiomyopathy (EVIDENCE-HCM).

BACKGROUND: Identification of people with hypertrophic cardiomyopathy (HCM) who are at risk of sudden cardiac death (SCD) and require a prophylactic implantable cardioverter defibrillator is challenging. In 2014, the European Society of Cardiology proposed a new risk stratification method based on a risk prediction model (HCM Risk-SCD) that estimates the 5-year risk of SCD. The aim was to externally validate the 2014 European Society of Cardiology recommendations in a geographically diverse cohort of patients recruited from the United States, Europe, the Middle East, and Asia. METHODS: This was an observational, retrospective, longitudinal cohort study. RESULTS: The cohort consisted of 3703 patients. Seventy three (2%) patients reached the SCD end point within 5 years of follow-up (5-year incidence, 2.4% [95% confidence interval {CI}, 1.9–3.0]). The validation study revealed a calibration slope of 1.02 (95% CI, 0.93–1.12), C-index of 0.70 (95% CI, 0.68–0.72), and D-statistic of 1.17 (95% CI, 1.05–1.29). In a complete case analysis (n= 2147; 44 SCD end points at 5 years), patients with a predicted 5-year risk of <4% (n=1524; 71%) had an observed 5-year SCD incidence of 1.4% (95% CI, 0.8–2.2); patients with a predicted risk of ≥6% (n=297; 14%) had an observed SCD incidence of 8.9% (95% CI, 5.96–13.1) at 5 years. For every 13 (297/23) implantable cardioverter defibrillator implantations in patients with an estimated 5-year SCD risk ≥6%, 1 patient can potentially be saved from SCD. CONCLUSIONS: This study confirms that the HCM Risk-SCD model provides accurate prognostic information that can be used to target implantable cardioverter defibrillator therapy in patients at the highest risk of SCD.post-print846 K

The selective reduction of NOx with NH3 over zirconia-supported vanadia catalysts

A series of sub-monolayer vanadia-on-zirconia catalysts have been prepared and the activities of these have been measured for the selective reduction of NO with NH3. It has been found that the activity per vanadium surface species depends on the square of the vanadium surface coverage. We therefore conclude that clusters of vanadia species on the surface of the catalysts are responsible for the de-NOx activity rather than isolated vanadia surface molecules

The selective reduction of NOx with NH3 over zirconia-supported vanadia catalysts

A series of sub-monolayer vanadia-on-zirconia catalysts have been prepared and the activities of these have been measured for the selective reduction of NO with NH3. It has been found that the activity per vanadium surface species depends on the square of the vanadium surface coverage. We therefore conclude that clusters of vanadia species on the surface of the catalysts are responsible for the de-NOx activity rather than isolated vanadia surface molecules

Electrochemical deprotonation of phosphate on stainless steel

Voltammetric experiments performed in phosphate buffer at constant pH 8.0 on platinum and stainless steel revealed clear reduction currents, which were correlated to the concentrations of phosphate. On the basis of the reactions proposed previously, a model was elaborated, assuming that both H2PO4 and HPO4 2 underwent cathodic deprotonation, and including the acid–base equilibriums. A kinetic model was derived by analogy with the equations generally used for hydrogen evolution. Numerical fitting of the experimental data confirmed that the phosphate species may act as an efficient catalyst of hydrogen evolution via electrochemical deprotonation. This reaction may introduce an unexpected reversible pathway of hydrogen formation in the mechanisms of anaerobic corrosion. The possible new insights offered by the electrochemical deprotonation of phosphate in microbially influenced corrosion was finally discussed

Comparison of optical probes and X-ray tomography for bubble characterization in fluidized bed methanation reactors

The performance of many fluidized bed reactors strongly depends on the bubble behavior since they influence the mass transfer to the dense phase where the catalyst is present. An example is the methanation in a fluidized bed that allows for conversion of unsaturated hydrocarbons in the gasification gas without catalyst deactivation [1]. The BFB reactor is a very challenging step in the process chain to produce SNG out of biomass as feedstock since next to the bubble behavior a lot of other parameters like temperature, pressure, particle size, attrition of the catalyst, internals, bed height and reactor diameter etc. affect the overall performance. The focus of this research work lies on the determination of the bubble properties which are an important factor to model a bubbling fluidized methanation reactor in order to predict and optimize its performance and to support its scale-up [2]. Tomographic methods such as X-ray measurements are often used to characterize bubbles in a fluidized bed. Compared to intrusive measurement, e.g. optical probing, this method possesses the advantage of measuring bubbles throughout the entire cross section. However, X-ray measurements cannot be applied to all installation, especially not in large scale plants. For these purpose, we have developed optical probes that can be employed to investigate the fluidization state in a hot pilot scale reactor. A main drawback of the optical measurements lies in their locally limited detection of the hydrodynamic pattern since they are only able to measure at one point in the reactor. Therefore, conclusions on the bubble behavior of the whole cross section based on optical measurements are not easy to derive. To compare the influence of the measurement method on the measured bubble properties, in the scope of this study, an artificial optical signal is created out of the existing X-ray measurement data set for a cold flow model of the pilot scale methanation reactor. The obtained bubble properties of both methods (i.e. evaluation of the derived artificial optical probe signal and image reconstruction based on the original X-ray tomographic data) are compared with regard to the hold-up, bubble rise velocity and the bubble size (for the X-ray method) or chord length (for the optical evaluation method), respectively. The process to obtain an artificial optical signal is depicted in Figure 1. The comparison shows that for the evaluation of optical probe data, statistical effects have to be considered carefully. The detected mean chord length of the optical method does not represent the mean bubble size determined by the X-ray method. Moreover, also a difference in the bubble rise velocity was detected for some fluidization states. This knowledge may be the basis for the derivation of a statistically sound method to calculate different hydrodynamic properties in fluidized bed reactors based on optical probe measurements. Please click Additional Files below to see the full abstract

Antarctic Volcanic Flux Ratios from Law Dome Ice Cores

Explosive volcanic eruptions can inject large quantities of sulphur dioxide into the stratosphere. The aerosols that result from oxidation of the sulphur dioxide can produce significant cooling of the troposphere by reflecting or absorbing solar radiation. It is possible to obtain an estimate of the relative stratospheric sulphur aerosol concentration produced by different volcanoes by comparing sulphuric acid fluxes determined by analysis of polar ice cores. Here, we use a non-sea-salt sulphate time series derived from three well-dated Law Dome ice cores to investigate sulphuric acid flux ratios for major eruptions over the period AD 1301-1995. We use additional data from other cores to investigate systematic spatial variability in the ratios. Only for the Kuwae eruption (Law Dome ice date AD 1459.5) was the H2SO4 flux larger than that deposited by Tambora (Law Dome ice date AD 1816.7)

A transient component in the pulse profile of PSR J0738-4042

One of the tenets of the radio pulsar observational picture is that the integrated pulse profiles are constant with time. This assumption underpins much of the fantastic science made possible via pulsar timing. Over the past few years, however, this assumption has come under question with a number of pulsars showing pulse shape changes on a range of timescales. Here, we show the dramatic appearance of a bright component in the pulse profile of PSR J0738-4042 (B0736-40). The component arises on the leading edge of the profile. It was not present in 2004 but strongly present in 2006 and all observations thereafter. A subsequent search through the literature shows the additional component varies in flux density over timescales of decades. We show that the polarization properties of the transient component are consistent with the picture of competing orthogonal polarization modes. Faced with the general problem of identifying and characterising average profile changes, we outline and apply a statistical technique based on a Hidden Markov Model. The value of this technique is established through simulations, and is shown to work successfully in the case of low signal-to-noise profiles.Comment: Accepted for publication in MNRA