A.L.N. Moreira

Thermocouples and sample probes for combustion studies

Abstract The importance and limitations of probe methods for making measurements in combusting systems are reviewed and discussed in terms of the contributions that they can make to improve the knowledge and the modelling of practical systems. Emphasis is on measurements of temperature, major species and ion concentrations, which are discussed in terms of the need to determine and minimize probe-induced disturbances in practical combusting flows. In addition, errors arising from the difficulty in interpreting the results in turbulent flames are discussed and the review also provides some insight into measurements of time-resolved scalar quantities.

Glutathione S-transferase mu polymorphism and susceptibility to lung cancer in the Portuguese population†

Epidemiological studies have led to the suggestion that a genetic basis may exist in the individual variation in predisposition to cancer. Interindividual differences in human toxicological response to carcinogenic exposure have been attributed to heritable polymorphisms in metabolism, namely glutathione S-transferases (GSTs) coding for enzymes that are known to be detoxifiers of carcinogens. Within the human GST mu class, there is a specific isozyme that is frequently lacking. To check whether or not this association exists in the Portuguese population with lung cancer, we used polymerase chain reaction (PCR)-based genotyping to examine GSTM1 polymorphism (nulled and non-nulled) in 84 individuals as a control healthy population and a group of 98 lung cancer patients. In this study we were able to find a frequency of the GSTM1 phenotype among our healthy control subjects consistent with earlier genotyping studies in other Caucasoid populations. For the group of individuals with lung cancer as a whole, or in subsets of histological subtypes, our data for the Portuguese population did not show a positive correlation between the null allele and this neoplasm. In contrast, we found a slight increase in the frequency of the wild-type allele in our lung cancer group.

Enhancement of pool boiling heat transfer by surface micro-structuring

The present paper addresses the use of surfaces structured with arrays of square micro-cavities to enhance pool boiling heat transfer. The heat transfer performance, obtained with the structured surfaces is evaluated based on the measured boiling curves and on the heat transfer coefficients. Two new parameters are suggested to relate the bubble dynamics (and consequently the surface topography) with the heat transfer coefficients: the modified dimensionless cavity spacing and the dimensionless distance, which cover the governing parameters of the phenomena. Correlations of these parameters with the heat transfer coefficients allowed to identify the best performing patterns, from those tested so far. Based on this progress it is expected that optimization of these relations will lead to precise relations which allow a systematic optimization of the surface pattern leading to an effective heat transfer enhancement, for situations involving high heat fluxes.

A real-time assessment of measurement uncertainty in the experimental characterization of sprays

This work addresses the estimation of the measurement uncertainty of discrete probability distributions used in the characterization of sprays. A real-time assessment of this measurement uncertainty is further investigated, particularly concerning the informative quality of the measured distribution and the influence of acquiring additional information on the knowledge retrieved from statistical analysis. The informative quality is associated with the entropy concept as understood in information theory (Shannon entropy), normalized by the entropy of the most informative experiment. A new empirical correlation is derived between the error accuracy of a discrete cumulative probability distribution and the normalized Shannon entropy. The results include case studies using: (i) spray impingement measurements to study the applicability of the real-time assessment of measurement uncertainty, and (ii) the simulation of discrete probability distributions of unknown shape or function to test the applicability of the new correlation.

Visualization and Analysis of Spray Impingement Under Cross-Flow Conditions

Gasoline Direct Injection (GDI) engines are becoming increasingly popular due to the potential to improve power and fuel consumption. The direct injection of gasoline inside an engine is classified in three types: wall-guided; air-guided; and spray-guided (also designated as air-assisted). In the wall-guided, spray impingement on the piston’s bowl head is part of the process to form a stratified charge near the spark plug, as well as to aid in the fuel mixture preparation. In the air-guided (swirl and tumble) and spray-guided, the impingement is undesirable. The interaction between the spray and the surrounding air, as well as the characteristics of the spray, are very important to achieve the benefits of the GDI concept. Although many works have been published which consider the structure of individual sprays, much remains to be known about the interaction between the spray and the wall in the presence of air motion. This is the goal of our work. For that an experimental facility has been built to study the fluid and thermodynamic behavior of a gasoline spray impinging onto a cold/heated surface under cross flow conditions. In a first step of our study we intend to build a fundamental basis on the influence of droplet size and velocity relatively to the cross flow and, therefore, used a PFI injector for easy of experimental analysis. Despite this injector operates at low pressure, images of the spray under quiescent conditions showed a spray quality similar to that of a DI injector, without injection of streams of liquid. Also, measurements obtained with a phase Doppler anemometer showed that droplet sizes range between 10µm and 120µm.

Temperature, Species and Heat Transfer Characteristics of A 250 MWe Utility Boiler

ABSTRACT This paper presents and discusses measurements of local flame temperature, local gas species concentrations and incident wall heat fluxes obtained in a 250 MWe residual fuel-oil front fired utility boiler. The work is aimed at improving knowledge of the efficiency of the thermal processes involved in large industrial boilers and covers three different operating conditions, which include load and air-fuel ratio variations. The measurements were made using special design probes through the ports available for inspection of the boiler. Local gas temperatures varied between 1650°C in the centre of the flames attached to the burners to around 1100°C close to the boiler nose, with maximum variations in the plane of the burners between the front and rear walls of about 200°C. The levels of CO were as high as 2% close to the ash pit and reach 1% near the boiler nose, suggesting some limitations in the process of fuel burnout and CO oxidation. Wall incident total heat fluxes varied between 200 k W/m2 and ...

On the analysis of turbulent transport processes in nonreacting multijet burner flows

Measurements of time-resolved velocity characteristics have been obtained with a laser-Doppler velocimeter in the vicinity of a model of an industrial oxy-fuel burner. The burner consists of a central axisymmetric jet surrounded by 16 circular jets, simulating the injection of oxygen in practical burners. The experiments were carried out for isothermal flows and quantify the effect of swirl for 0 ≤ S ≤ 0.9 on the mixing efficiency of the burner assembly.The results show that the present flow develops faster than related coaxial free jets with similar velocity ratios between central and peripheral air streams and, for example, for the nonswirling flow the rate of decay of the centreline velocity increases by a factor of 2. Swirl attenuates the three-dimensional structure typical of multijet flows although the peripheral jets limit the radial spreading of the swirling flow and give rise to increased values of mean shear strain and, therefore, to turbulent production. The existence of zones characterized by large turbulence anisotropy indicate the need to take account of the individual normal stresses in any proposed mathematical model to simulate the flow characteristics. Inspection of the terms in the conservation equation for the turbulent stresses quantify the extent to which interaction of normal stresses with normal strains influences the flow and suggests the likely combined magnitude of turbulent diffusion and dissipation.

Velocity characteristics of a swirling recirculating flow

Abstract The isothermal recirculating flow downstream of a model swirl burner is studied making use of a laser-Doppler velocimeter. The arrangement was designed to incorporate the injection of liquid fuel into a gas flame characterized by a large recirculation zone attached to the burner head and to allow a detailed analysis of turbulent transport processes in a strongly swirled recirculating flow. The results show that turbulent mixing in the present isow is not dominated by large-scale motions or precission. The production of turbulent kinetic energy depends upon mechanisms of shear-generated turbulence but is influenced by streamline curvature in the zone of mean shear. Inspection of the terms in the conservation equations for the turbulent stresses allows quantification of the extent to which the interaction of normal stresses and normal strains influence the flow and suggests the likely magnitude of turbulent diffusion and dissipation.

On the influence of a plasma hot component on whistler propagation beyond the plasmapause

Theoretical spectrograms are computed for whistlers propagating beyond the plasmapause. The electron distribution function was modelled as consisting of a hot plus a cold component and an appropriate dispersion equation is used. A collisionless (CL) model is used for the cold electron concentration and for the hot electron component the derived model assumes a bi-maxwellian distribution function with a loss cone at the equator. The results indicate limits on the use of the cold plasma approximation (c.p.a.) in the study of magnetospheric whistler propagation beyond the plasmapause and show that whistler analysis with the c.p.a. may under or overestimate the L value of the path deduced from ground spectrograms, depending on the anisotropy of the hot component.

The Deformation of Single Droplets Impacting onto a Flat Surface

This paper presents an experimental study of the deformation of spherical liquid droplets impinging onto dry and flat surfaces making use of a CCD-camera with a high spatial resolution. The experiments consider different liquids (water and Diesel oil) and the effects of droplet velocity and diameter at the impact in a range of Weber numbers up to 1100 and Reynolds numbers up to 77400. Emphasis is put on the nature of the surface target. To consider this effect, two surface materials were used (Perspex and aluminium) with surface roughness varying from less than 5µm (considered as a smooth surface) up to Ra=66,6µm. For the range of droplet diameters considered in the experiments, the corresponding dimensionless values of Ra/Rdroplet vary from 1,5x10 -5 and 2,5x10 -2 . In a first step, the experiments focus on the spread of the liquid film and analysis of the results suggest that, provided that the Reynolds number of the droplet at the impact is large (Re>2000), the energy dissipated at the wall is not affected by the nature of the surface. The effect of surface roughness appears to be important for low Reynolds numbers, typically Re<1000. Depending upon the physical parameters at the impact, the droplet may splash at the first contact with the surface (prompt splash) or the liquid film at the wall may break-up on secondary droplets during spread. In a second step, the experiments emphasize the effect of surface roughness on the onset of splash for different liquids. The experimental results are analysed in terms of the critical Weber number for which splash occurs, and compared with correlations reported in the literature accounting for the effects of surface roughness and droplet liquid and suggest the likely influence of, not only the nature of the surface (e.g. surface profile and material), but also of the liquid.