Thermal-hydraulic and optical modeling of solar Direct Steam Generation systems based on Parabolic-Trough Collectors

Not only the round absorber tube has been studied, but as a matter of example, the potential of the IMCRT method has also been applied to flat absorbers. A thermal model of a linear receiver has also been performed to describe the heat transfer mechanisms between all the elements on it. Heat diffusion in the absorber tube wall as well as the glass cover has been modeled in 3D, whereas the fluid domain (superheated steam) has been simplified according to a 1D approach. Results have been validated with experimental data from the DISS facility located at Plataforma Solar de Almería. Besides, a detailed thermal-hydraulic study has also been carried out by means of the commercial code RELAP5. This code is based on a transient two-fluid model where both, single-phase and two-phase flow regions can be simulated. Thermal behavior of the absorber tube can also be approximated by means of the standard capabilities of RELAP5. A full and detailed model of the DISS facility has been performed where the connection pipes between adjacent collectors have been included. This model has been validated with experimental data obtained from full day tests getting a good agreement. According to the results, the 1D approach followed by RELAP5 is able to reproduce transient phenomena which usually take place in common operation conditions. In addition, heat losses have been experimentally characterized in the same facility. A new correlation, which takes into account heat losses of receivers after two years and a half of operation, is proposed and included in the model. Thermal-hydraulic codes also make it possible to study severe slugging in connection pipes. For that purpose, a particular connection pipe alongside their two adjacent collectors have been simulated to figure out in which range of operation conditions severe slugging occurs at a pressure of 0.5 MPa.CSP systems based on Parabolic-Trough Collectors (PTCs) account for a representative share of the global solar thermal capacity installed. Most of the existing PTC power plants use synthetic oil as heat transfer fluid. However, water can be alternatively used, where both single and two-phase flow occur. This technology is called Direct Steam Generation (DSG) and it presents some advantages in terms of system overall efficiency and plant cost reduction. Nevertheless, some complexities inherent to two-phase flow have to be addressed to succeed in the commercial deployment of DSG. The development of numerical codes to model such systems is of key importance to put new insights into them. Both, the thermal-hydraulic and optical modeling are of relevance. Conventional parabolic-trough reflectors concentrate solar radiation on absorber tubes following a characteristic pattern with a non-homogeneous distribution in the angular direction. It means that the bottom half of the absorber tube receives much more flux than the upper half. Under specific two-phase flow patterns (e.g. stratified flow) the refrigeration of the absorber tube is not homogeneous and thermal bending may take place. This problem can also be reported in single-phase flow conditions (e.g. superheated steam), where a significant thermal gradient at the cross-sectional plane of the absorber tube can be critical. A new technique called Inverse Monte Carlo Ray Tracing (IMCRT) method is proposed in this thesis. It aims to design new reflector geometries so that a more homogeneous distribution of concentrated solar radiation on the absorber tube can be accomplished. In line with this, new reflector geometries have been proposed with the same aperture width as the LS-3 design for the same absorber design, where quasi-constant flux distribution is achieved within a specific angular range

Global stability map of the flow in a horizontal concentric cylinder forced by natural convection.

There are a large number of studies in the literature on natural convection in the annulus between horizontal concentric cylinders. However, not many publications dealing with global stability analysis in this kind of flow have been published. For a fixed diameter ratio L/Di = (Ro − Ri)/2Ri, being Ri and Ro the inner and outer cylinder radii respectively, and assuming Boussinesq approximation, the solution only depends on Prandtl (P r ≡ ν/α) and Rayleigh (Ra ≡ g β L3 (Ti − To)/(ν α)) numbers. A spectral collocation code has been developed to solve the problem by means of Chebyshev and Fourier differentiation matrices for L/Di = 0.8 and it has been validated with classical experimental results. Steady solutions have been sought within the range P r ∈ [1e−2, 1] and Ra ∈ [1e-2, 5e6]. As a result, a steady solution Pr-Ra map (consisting of 149 x 75 points) has been traced, where the different families of similar solutions found are detailed, mainly characterized by presenting single or multiple plumes. In addition, two main double-solution regions have been found

Influence of Reynolds number on theoretical models for trailing vortices

We conduct direct numerical simulations for a NACA0012 airfoil at Reynolds numbers (Re) ranging from 300 to 7000 to determine the wake behavior behind this wing profile. We characterize the structure of the wing-tip vortex, finding a reasonable agreement with experimental results at Re=7000. In addition, we model the trailing vortex theoretically, thus obtaining the parameters for Batchelor’s and Moore and Saffman’s models. We compare the results of the best fitting for the axial vorticity and the azimuthal velocity, finding only small discrepancies. The main contribution of this research work is to study the evolution of these theoretical parameters as function of the Reynolds number. We observe that the wake becomes unstable at Re ≈1200, in agreement with previous results. These instabilities in the wake behind the wing produce a change in the trend of theoretical parameters (keywords: vortex dynamics, trailing vortices, theoretical models).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Experimental observations of trailing vortices at high Reynolds numbers

Experimental techniques applied to the study of wingtip vortices are of great interest for the Fluid Mechanics Community. The available experimental techniques to obtain new insights into trailing vortices, focus on quantitative methods, e.g. Particle Image Velocimetry (PIV)1,2. In fact, this technique requires high costs associated not only to equipments but also to image processing that is a complex, and time consuming task. A novel, easier, faster and cheaper experimental procedure is presented in this research work to compute experimentally the vortex structure in comparison to a theoretical model. Different theoretical models have described the velocity field for every cross section along the axial coordinate, once the vortex was created at the wing tip. These models depend on several parameters and provide the axial evolution of the velocity field. We used in this study a q-vortex or Batchelor’s3 model, based only on two free parameters: swirl value, q, and the virtual origin in the axial coordinate, z0. These parameters have been processed with the experimental trailing vortex formed by a NACA0012 aerofoil over a Reynolds number range of 105. The experimental setup consists of one smoke wire device together with a laser beam, and a digital camera installed in a subsonic wind tunnel. A smoke segment was generated upstream the model, but near the wing edge. This line followed the main stream passing through the wing tip. Lift forces produced the characteristic vortex pattern, highlighted by the swirling smoke segment, and whose topological structure was recorded by a digital camera. Several sections at different axial distances from the wing edge have been analyzed. The integration of the velocity field in the theoretical model allowed us to know two theoretical parameters in order to obtain similar experimental streaklines at a given axial position, as shown in figure 1. The experimental results using this procedure were in agreement with those found in the literature1.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work has been supported by the Grant Proyecto de Excelencia nº TEP-7776

Global stability analysis of the natural convection between two horizontal concentric cylinders

In this investigation, the 2D flow between two horizontally positioned concentric cylinders (gravity per- pendicular to the axis of the cylinders), where the inner cylinder is kept at constant temperature Ti higher than the outer border temperature To, is analyzed. Buoyancy forces initiate the movement of the fluid and the generated flow is studied in a fixed geometry for values of Prandtl numbers (Pr) between 0.01 and 1, and Rayleigh numbers (Ra) between 102 and 5 · 106 . To solve the problem, a Chebyshev-Fourier spectral code is developed in polar coordinates (r, θ ) respectively, and a complete map of steady-state solutions is obtained where regions with multiple solutions are identified. Later, a global stability study of the ob- tained stationary solutions is carried out, providing a transition curve to unstable areas as a function of the control parameters of the problem (Pr, Ra). Finally, to check the stability results, temporal evolution simulations are accomplished for several cases where dual solutions are presented, finding intermediate almost stationary solutions, and demonstrating that there exist typically single oscillating plume or dou- ble oscillating plume solutions (depending on the parameter space), where some of them have higher heat transfer coefficients, which may be interesting alternatives to improve heat exchange systems by means of passive control techniques.Funding for open access charge: Universidad de Málaga / CBUA. First author J.J. Serrano-Aguilera acknowledges the support provided by Ministerio de Ciencia, Innovación y Universidades (Spain) by means of the postdoc position: Ref No. FJCI-2017-32403 (Juan de la Cierva-Formación Postdoc Grant), as well as to Junta de Andalucía for the funding for the HERTERSOL project (UMA18-FEDERJA-195). Francisco J. Blanco-Rodríguez also acknowledges funding received from the Spanish Government program Juan de la Cierva-Incoporación through grant IJCI-2016-30126. Most of the numerical simulations have been carried out in Picasso, a RES node located in the Bio-Innovation Building of the University of Málaga (UMA) at the Technological Park of Andalusia (PTA)

Evaluación por competencias en asignatura troncal de Mecánica de Fluidos

Este trabajo presenta una propuesta de evaluación por competencias para una asignatura troncal de Mecánica de Fluidos. Se propone eliminar el examen final para la evaluación del aprendizaje por una evaluación continua de cada uno de los objetivos de aprendizaje. La evaluación continua consiste en la resolución de problemas con múltiples respuestas en el aula de informática. Para demostrar la adquisición de la competencia definida en el objetivo de aprendizaje el alumno deberá responder correctamente al menos un 80% de los problemas propuestos para cada uno de ellos, con un mínimo de 10 problemas por objetivo. Este tipo de evaluación asíncrona se puede llevar a cabo en las horas de tutoría y permite la corrección automática de las mismas, consiguiendo simultáneamente un triple objetivo: (i) liberar de carga de trabajo al docente; (ii) asegurar un mínimo de calidad en la evaluación de la adquisición de las habilidades requeridas en una asignatura troncal y (iii) hacer responsable al alumnado de su propio aprendizaje, pudiendo evaluarse en cualquier momento del semestre y repitiendo la evaluación.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Transmitted drug resistance to antiretroviral drugs in Spain during the period 2019–2021

To evaluate the prevalence of transmitted drug resistance (TDR) to nucleoside and nonnucleoside reverse transcriptase inhibitors (NRTI, NNRTI), protease inhibitors (PI), and integrase strand transfer inhibitors (INSTI) in Spain during the period 2019-2021, as well as to evaluate transmitted clinically relevant resistance (TCRR) to antiretroviral drugs. Reverse transcriptase (RT), protease (Pro), and Integrase (IN) sequences from 1824 PLWH (people living with HIV) were studied. To evaluate TDR we investigated the prevalence of surveillance drug resistance mutations (SDRM). To evaluate TCRR (any resistance level >= 3), and for HIV subtyping we used the Stanford v.9.4.1 HIVDB Algorithm and an in-depth phylogenetic analysis. The prevalence of NRTI SDRMs was 3.8% (95% CI, 2.8%-4.6%), 6.1% (95% CI, 5.0%-7.3%) for NNRTI, 0.9% (95% CI, 0.5%-1.4%) for PI, and 0.2% (95% CI, 0.0%-0.9%) for INSTI. The prevalence of TCRR to NRTI was 2.1% (95% CI, 1.5%-2.9%), 11.8% for NNRTI, (95% CI, 10.3%-13.5%), 0.2% (95% CI, 0.1%-0.6%) for PI, and 2.5% (95% CI, 1.5%-4.1%) for INSTI. Most of the patients were infected by subtype B (79.8%), while the majority of non-Bs were CRF02_AG (n = 109, 6%). The prevalence of INSTI and PI resistance in Spain during the period 2019-2021 is low, while NRTI resistance is moderate, and NNRTI resistance is the highest. Our results support the use of integrase inhibitors as first-line treatment in Spain. Our findings highlight the importance of ongoing surveillance of TDR to antiretroviral drugs in PLWH particularly with regard to first-line antiretroviral therapy

Association between long term exposure to particulate matter and incident hypertension in Spain

Exposure to air particulate matter has been linked with hypertension and blood pressure levels. The metabolic risks of air pollution could vary according to the specific characteristics of each area, and has not been sufficiently evaluated in Spain. We analyzed 1103 individuals, participants in a Spanish nationwide population based cohort study ([email protected]), who were free of hypertension at baseline (2008-2010) and completed a follow-up exam of the cohort (2016-2017). Cohort participants were assigned air pollution concentrations for particulate matter < 10 mu m (PM10) and < 2.5 mu m (PM2.5) during follow-up (2008-2016) obtained through modeling combined with measurements taken at air quality stations (CHIMERE chemistry-transport model). Mean and SD concentrations of PM10 and PM2.5 were 20.17 +/- 3.91 mu g/m(3) and 10.83 +/- 2.08 mu g/m(3) respectively. During follow-up 282 cases of incident hypertension were recorded. In the fully adjusted model, compared with the lowest quartile of PM10, the multivariate weighted ORs (95% CIs) for developing hypertension with increasing PM10 exposures were 0.82 (0.59-1.14), 1.28 (0.93-1.78) and 1.45 (1.05-2.01) in quartile 2, 3 and 4 respectively (p for a trend of 0.003). The corresponding weighted ORs according to PM2.5 exposures were 0.80 (0.57-1.13), 1.11 (0.80-1.53) and 1.48 (1.09-2.00) (p for trend 0.004). For each 5-mu g/m(3) increment in PM10 and PM2.5 concentrations, the odds for incident hypertension increased 1.22 (1.06-1.41) p = 0.007 and 1.39 (1.07-1.81) p = 0.02 respectively. In conclusion, our study contributes to assessing the impact of particulate pollution on the incidence of hypertension in Spain, reinforcing the need for improving air quality as much as possible in order to decrease the risk of cardiometabolic disease in the population