Fluidization of Group B particles with a rotating distributor

A novel rotating distributor fluidized bed is presented. The distributor is a rotating perforated plate, with 1% open-area ratio. This work evaluates the performance of this new design, considering pressure drop, Δp, and quality of fluidization. Bed fluidization was easily achieved with the proposed device, improving the solid mixing and the quality of fluidization. In order to examine the effect of the rotational speed of the distributor plate on the hydrodynamic behavior of the bed, minimum fluidization velocity, Umf, and pressure fluctuations were analyzed. Experiments were conducted in the bubbling free regime in a 0.19 m i.d. fluidized bed, operating with Group B particles according to Geldart's classification. The pressure drop across the bed and the standard deviation of pressure fluctuations, σp, were used to find the minimum fluidization velocity, Umf. A decrease in Umf is observed when the rotational speed increases and a rise in the measured pressure drop was also found. Frequency analysis of pressure fluctuations shows that fluidization can be controlled by the adjustable rotational speed, at several excess gas velocities. Measurements with several initial static bed heights were taken, in order to analyze the influence of the initial bed mass inventory, over the effect of the distributor rotation on the bed hydrodynamics.Publicad

The water cost effect of hybrid-parallel condensing systems in the thermo-economical performance of solar tower plants

The importance of considering the water price in the analysis of the impact of dry versus hybrid condensing systems in the thermo economical performance of solar tower plants was demonstrated in this work. The dry condensing system consists of several induced-draft air-cooled condenser cells (ACCs) and the hybrid system consists of a parallel system where the condensing steam is split between the ACCs and a surface steam condenser where circulating water is cooled in a wet mechanical-draft cooling tower. The influence of the operating parameters of either the dry or wet cooling systems on the cooling load and fan power consumption were studied. Then, for a given condensing system (a system with a defined number of installed ACCs units and cooling tower units) and given the dry-air and wet-bulb air temperatures, the operating parameters were optimized to maximize the revenues of the power plant. This optimization depends on the water-to-electricity price ratio , showing that at low ambient temperature when this ratio increases it is not profitable to turn on the cooling towers since the water cost is not counterbalanced by the higher cycle efficiency obtained with the lower condensation temperature. Finally, the annual operation and the LCOE and NPV of the CSP plant located in Dunhuang were analyzed for both dry and hybrid condensing systems with different number of ACCs and wet towers, showing that the most cost-effective configuration is the 16 ACCs with 3 wet cooling towers for water-to-electricity price ratio = 4 ($/m3)/($/kWhe) and = 5 ($/m3)/($/kWhe), but for = 10($/m3)/($/kWhe), the best option is with only 2 wet towers.This research is partially funded by the Spanish government under the project RTI2018-096664-B-C21 (MICINN/FEDER, UE)

Economic and thermo-mechanical design of tubular sCO2 central-receivers

Supercritical CO2 central-receivers must withstand high temperatures and pressures combined with cyclic operation, which makes the solar receiver susceptible to creep-fatigue failure. In this work, a creep-fatigue analysis of a sCO2 Inconel 740H tubular receiver of a 2 MWe solar tower plant has been accomplished to study the influence of the tube size on the receiver and solar field design. A 2D numerical model of the tubular receiver that accounts for the thermal conduction in both radial and circumferential directions was developed to determine the sCO2 and wall temperature profile, which is crucial for the creep-fatigue calculations. The receiver flux distribution, which is an input to the model, was obtained with SolarPILOT, while a conventional recompression model was used to calculate the cycle efficiency and inlet temperature to the receiver. Comparison of the results of the 2D model with those of a 1D model showed that the 1D model overestimates the creep fatigue rupture time by two orders of magnitude. Furthermore, the efficiency and costs of the heliostat field and receiver were calculated for different receiver tube sizes. Smaller tubes allowed a higher maximum heat flux leading to smaller receiver and heliostat field designs, which resulted in higher overall efficiency of the power plant and lower material costs. For a design ensuring 25 year receiver lifetime the minimum sCO2 solar receiver cost, 345 €/kWth, was obtained for the smallest pipe diameter.This research is partially funded by the Spanish government under the projects RTI2018-096664-B-C21 (MICINN/FEDER, UE) and RED2018-102431-T (AEI, MICINN) and the fellowship “Programa de apoyo a la realizaci on de proyectos interdisciplinares de I+D para j ovenes investigadores de la Universidad Carlos III de Madrid 2019e2020” under the project ZEROGASPAIN-CM-UC3M (2020/00033/001), funded on the frame of “Convenio Plurianual Comunidad de Madrid-Universidad Carlos III de Madrid 2019e202”

Exergy Optimization of a Moving Bed Heat Exchanger

The MBHE proposed can be analyzed as a crossflow heat exchanger where one of the phases is a moving granular medium. In the present work the exergy analysis of the MBHE is carried out over operation data of the exchanger obtained in two ways: a numerical simulation of the stationary problem and a simplified analysis. The numerical simulation is carried over the two steady state energy equations (fluid and solid), involving (for the fluid) the convection heat transfer to the solid and the diffusion term in the flow direction, and (for the solid) only the convection heat transfer to the fluid. The simplified analysis followed the well-known e-NTU method, taking the equipment as a crossflow heat exchanger with both fluids unmixed.Publicad

Experimental study of the preheating process of tubular external molten salt receivers

Proceeding of: XI National and II International Engineering Thermodynamics Congress (11 CNIT 2019)In this work, the heat transfer process of the tubes of a central receiver of a CSP plant during the start-up is studied. With this aim, the temperature of the external surface of the pipe is measured in a molten salt test loop. The experimental installation is formed by a cylindrical molten salt tank, a pump to circulate the molten salt through a pipe in a close circuit and an induction heater to generate the heat flux, which is applied in a small rectangular region of the tube surface. The temperatures were measured with the empty tube subjected to a high heat flux of approximately 200 kW/m2 . Once the tube reached a high temperature of approximately 800 º C, Solar Salt (a mixture of potassium and sodium nitrate in a proportion of 60/40 % wt.) started to circulate inside the tube. This process simulates the start-up process of a central tower plant, when the heliostat field focuses on the receiver to preheat the tubes prior to filling the receiver with molten salt. Central tower receivers are subjected to a unilateral concentrated solar radiation that causes a high temperature difference between the tube crown at the outside surface of the tube, which receives the highest solar radiation, and the back surface of the tube, which is in shadow. This temperature difference leads to the mechanical strain of the tube. In order to study the effects of this non-homogenous heat flux, temperatures and tube deflection of the pipe were measured at different experimental conditions. Several K-type thermocouples were welded at different azimuthal and axial positions of the pipe to measure the external surface temperature. Additionally, images of the pipe were taken during the heating process to measure the deflection of the tube.The authors would like to thank the financial support from Ministry of Economy and Competitiveness (Projects ENE2012-34255 and ENE2014-54942-R) and the Ministry of Education, Culture and Sport under the program of Formación del Profesorado Universitario (FPU14/04941)

Las parlamentarias regionales en España: masa crítica, experiencia parlamentaria e influencia política Women MPs in Spanish Regional Parliaments: Critical Mass, Parliamentary Experience and Political Influence

Este trabajo analiza la evolución de la proporción de mujeres en los 17 parlamentos regionales españoles desde 1980 hasta 2011. En línea con el argumento de la masa crítica en su versión de representación descriptiva, se pone a prueba si, una vez se llega a un umbral del 30% de parlamentarias, la proporción de éstas no cae por debajo de dicho umbral. Se contrastan a continuación dos hipótesis acerca de la presencia política de las mujeres: la que defiende que la experiencia parlamentaria (‘incumbency’) reduce las diferencias de género en las expectativas de conseguir un escaño; y la que afirma que las mujeres son relegadas a posiciones de escasa influencia en el legislativo

Characterization of flow-induced vibrations in gas-solid fluidized beds: elements of the theory

This paper revisits the basic hypothesis underlying the measurement of flow-induced vibration in fluidized beds. A novel theoretical approach based on the standing pressure field characterizing the bed dynamics is proposed to link the pressure fluctuations to the measured accelerometer signals. The model provides a reliable prediction of the carrying frequency band and helps in designing the accelerometer measurement process. The model was tested with previous results reported in the literature as well as with piezoelectric accelerometer measurements collected from a lab-scale experimental facility. A study on accelerometer measurements was conducted to identify the main limitations expected for measuring flow-induced vibrations in a gas-solid fluidized bed. The structural response of the vessel to flow-induced vibration was mostly determined by the "bed acoustics" that can be dominated by either elastic or compression waves. Finally, the survival of an envelope process on the measured accelerometer signal guaranteed the quality of the flow dynamical information collected during the measurement process.Financial support from projects DPI2009-10518 (MICINN) and CARDENER-CM (S2009ENE-1660).Publicad

Osteodistrofias en el perro y en el gato : diagnóstico diferencial

El presente trabajo intenta hacer un protocolo del diagnóstico de las osteodistrofias según las diferentes publicaciones revisadas, así como por la propia experiencia de los autores.In this present work I am traying to do a protocol of the diagnosis of the osteodistrophies according to the different revised publications as well as the personal experience of the authors

Heat generation depth and temperature distribution in solar receiver tubes subjected to induction

Induction heating is commonly used in laboratory-scale facilities to replicate the heating conditions of the receiver tubes of concentrated solar power plants. This work aims at shedding light at the induction heating characteristics for such applications through the development of a multiphysics numerical model capable of replicating the experimental conditions of a molten salt loop locally heated by an induction heater. In the experiments, a stainless steel pipe is heated on its external surface by the induction heater, which is switched on and off during the experimental data acquisition while molten salts are continuously circulating in its interior. These conditions are replicated, for the first time, in a two-dimensional numerical domain fully coupling the electromagnetic and thermal physics, including thermally dependent material properties of the heated pipe. Once validated against the experiments, the numerical results revealed that the volumetric nature of the induction heating shall be considered for an accurate representation of the temperature profile inside the tube. As a novelty, different equivalent surface boundary conditions are presented and, despite the Gaussian-like behavior of the induction heating on the surface of the tube, the results indicate that there exists no equivalent wall boundary condition to fully replicate the temperature profile obtained with the induction heater. The effect of independently varying experimental parameters such as the geometry of the pipe (i.e., diameter and thickness) and its distance to the induction heating system is also evaluated. Using large diameters of the tube reduces the difference between the angular temperature profile obtained using induction heating and a simplified wall boundary condition. For small wall thicknesses, the induction heating is capable of penetrating along the whole thickness of the tube, the total heat generated in the volume of the tube being exposed to the counteracting effects of the volumetric generation and the enhancement of the heat dissipation by the molten salt, as both of them increase for small thicknesses. The distance of the inductor to the pipe wall appears to maintain the volumetric characteristics of the heating and only affects the induction heating magnitude and efficiency.This work has been funded by Programa de Atracción de Talento (Modalidad 2) de la Comunidad de Madrid (Spain) 2019-T2/AMB-15938 and the project RTI2018-096664-B-C21 (MICINN, FEDER/UE). Eduardo Cano-Pleite acknowledges support from the CONEX-Plus programme funded by Universidad Carlos III de Madrid and the European Union's Horizon 2020 programme under the Marie Sklodowska-Curie grant agreement No. 801538