Esteban Calvo

PARTICLE CONCENTRATION AND LOCAL MASS FLUX MEASUREMENTS IN TWO-PHASE FLOWS WITH PDA. APPLICATION TO A STUDY ON THE DISPERSION OF SPHERICAL PARTICLES IN A TURBULENT AIR JET

Abstract The Phase Doppler Anemometry (PDA) technique is suitable for spherical particle concentration and local flux measurements in dispersed two-phase flows. When particles have three-directional paths, accurate measurements can be achieved if an integral method of calculation over the effective probe volume and an efficient auto-calibration process are employed. An experimental study is carried out on an axisymmetric two-phase jet. A post-processing of the measurements has been developed to obtain a quite complete characterisation of the particle dispersion throughout the flow. The axial local flux distribution is normalised on the transversal sections with the injected mass rate for each particle size class (by means of correction coefficients). Particle concentration and radial fluxes are calculated from the axial flux and velocity results. A balance of particles over a cylindrical volume permits to calculate further estimates of the particle radial flux, used for testing of the results. The detailed study of the spatial distribution of particles has been made up to 10 nozzle diameters (10D) from the jet exit, in five transversal sections. The local axial flux profiles show two development sub-zones: (i) the near to nozzle zone is dominated by the exit conditions. Mainly, a wide distribution of particle path directions produces a strong radial particle transference (directional classification); (ii) the second sub-zone shows a more regular development controlled by the drag of the mean gas velocity field together with radial particle transport by gas turbulence, rebounding crashes of particles and other effects.

A framework about flow measurements by LDA–PDA as a spatio-temporal average: application to data post-processing

Phase Doppler anemometry (PDA) is a well-established technique to study two-phase flows and its principles are also used in laser Doppler anemometry (LDA) for measurements of fluid velocity. Raw measurements of individual particle data require post-processing to obtain useful and consistent information (moments of velocity, particle concentration and flux, velocity autocorrelation, etc). This is called in this paper the reconstruction of statistical information. In the 1970s, several basic algorithms to perform the statistical reconstruction were developed for LDA measurements (such as the transit time method, the inverse velocity method, etc). With the advent of PDA, the scientific community developed reconstruction algorithms to obtain mean variables of the dispersed phase. All these basic algorithms were expounded as unconnected methods, following independent threads not integrated into a general framework. Assuming that the PDA works under ideal conditions (all particles that cross the probe volume are validated), this paper provides a general formulation and fully systematizes a large set of previous statistical reconstruction methods. In this paper, the statistical reconstruction of both the dispersed and the continuous phase is unified: the continuous phase post-processing emerges as the same reconstruction method of the dispersed phase. The general framework proposed offers many advantages. First, some previous calculation methods of particle concentration turn out to be particular cases of this general formulation. Second, it provides an easy way to deduce unbiased estimators of any statistical parameter of the flow. Third, a wide set of new post-processing methods are proposed to be tested by any member of the scientific community. In the fourth place, the generalized integral method to compute the particle concentration also gives information about the probe volume geometry and two new auto-calibration algorithms are proposed: the integral calibration method and the cross-section integral calibration method. Finally, a physical interpretation of the statistical reconstruction process is provided: it is a spatio-temporal averaging of the detected particle data, and some of the algorithms used are related to the Eulerian–Eulerian mathematical description of multiphase flows.

Mode transitions in an oscillating liquid sheet

Longitudinal oscillations in air-blasted or air-assisted liquid sheets have been the subject of a large number of papers in the last 30 years. Frequency and sometimes amplitude are the main parameters used to characterize these oscillations. Attending to them, and also in dependence on the surface topology (e.g., the presence of perforations or ligaments), several oscillation modes have been described. In most works, two or at most three regimes are considered. Following these previous descriptions, this experimental work has found that some submodes can also be discerned. Based on visual observations, frequency measurements, and spray angle calculations, for some liquid and air flow rates up to six modes have been observed with defined transitions among them. The different modes are analyzed and characterized, and their presence is related to the flow conditions.

Influence of liquid properties on ultrasonic atomization

Ultrasonic atomization is very convenient because it can generate droplets with diameters of a few microns andwith very narrow size distribution. Besides, opposite to twin fluid nozzles, in ultrasonic atomization, dropletgeneration and transport are decoupled processes. Droplets are ejected from the liquid surface with very lowvelocities, so driving them is relatively simple. Although this atomization method is now common in some specificapplications, for example in household humidifiers, there are still some details about the physics of this processthat are not completely understood. Up to date, most of the published results have been limited to experimentswith water. However, it has been demonstrated that atomization rates quickly decrease as liquid viscosityincreases. This work analyzes the characteristics of ultrasonic atomization of some alternative fluids to determineif there is any influence of other physical properties such as surface tension or vapor pressure. Experiments areperformed using a commercial piezoceramic disk with a resonance frequency of 1.65 MHz. The disk is excitedwith a sinusoidal signal with voltage amplitudes that go up to 60 V. Sprays are visually characterized analyzinginstantaneous images and high speed video sequences. Besides atomization rates are calculated by measuringthe weight loss in a fixed time. DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4588

THU0539 Sarcoidosis in spain: clinical and epidemiological characteristics at diagnosis in 1082 patients

Objectives To characterize the main features at presentation of sarcoidosis in a large multicenter cohort from Southern Europe. Methods In January 2016, the Autoimmune Diseases Study Group (GEAS-SEMI) created a national registry (SARCOGEAS) of patients with sarcoidosis. Sarcoidosis was diagnosed in agreement with the criteria proposed by the ATS/ERS/WASOG 1999 statement, and extrathoracic disease was classified with the 2014 WASOG instrument. Results The cohort consisted of 1082 patients (82% biopsy-proven), including 618 (57%) women and 464 (43%) men, with a mean age at diagnosis of 47yrs; 140 (13%) patients were born outside Spain, 965 (89%) were White, 69 (6%) Hispanic, 30 (3%) Black/African American and 18 (2%) Asian. Thoracic involvement was present at diagnosis in 979 (90%) patients, including 437 (40%) patients with stage I, 374 (35%) with stage II, 123 (11%) with stage III and 26 (2%) with stage IV. The most frequently reported extrathoracic involvements at diagnosis were cutaneous in 385 (36%) patients, extrathoracic lymph nodes in 218 (20%), liver involvement in 151 (14%) and ocular involvement in 118 (11%). Potentially life-threatening WASOG involvements were reported in frequencies less than 10%, including neurological involvement in 77 (7%) patients, kidney involvement in 59 (5%) or cardiac involvement in 21 (2%). Therapeutic approaches at diagnosis included the use of oral glucocorticosteroids in 637 (59%) patients, immunosuppressive agents in 84 (8%, mainly methotrexate in 63 patients) and biological agents in 15 (1%, mainly infliximab in 10 cases). Conclusions In this large series of sarcoidosis from Southern Europe, clinical presentation is dominated by adenopathies (both thoracic and extrathoracic) and cutaneous involvement (erythema nodosum), with lower frequencies in the main extrathoracic involvements than that reported in US and Japanese series. Disclosure of Interest None declared