Effects of the aeration on the fluid dynamic behaviour of a multi-zone activated sludge system

Conventional wastewater treatment plants (WWTP) are necessary to modify the wastewater properties in order to make it acceptable for a safe discharge into the environment or a certain reuse purpose. Biological oxidation is the most important of the processes involved in conventional WWTP. Organic substances dissolved in the water are removed by means of bacteria presented in the biological reactor. Air is necessary to enable the reduction of the organic content of the water by the bacteria. Bubbles of air are introduced into the reactor through air diffusers. Air diffusers can account up to 70% of WWTP total energy consumption. So a deep understanding of the dynamic behaviour of the flow is necessary for optimizing the process and saving energy. A numerical analysis of the effects of the aeration in the fluid dynamics behaviour of a real multi-zone activated sludge reactor is carried out. The purpose is to identify and analyse the changes originated in the velocity field by the aeration. A numerical modelling of the activated sludge system located in San Pedro del Pinatar (Murcia, Spain) is developed throughout a general-purpose computational fluid dynamics (CFD) code. The multiphase flow is simulated with a Euler–Lagrange approach; modelling the bubbles as discrete phase. Two simulations, one with aeration and the other without it, are carried out. The numerical results show that the aeration has a notable effect in the performance of the reactor. Changes in velocity field, stagnant zones, residence time distribution or even free surface level originated by the aeration in the reactor are studied. In general, the aeration reduced the amount of stagnant volume in the reactor. However, when the aeration is activated, some re-circulating zones are formed, reducing the residence time in the reactor.The researcher team of the present work acknowledges the contribution of the company ESAMUR, owner of the biological reactor studied, which provided the experimental data necessary for the development of the numerical model presented

In-pipe axial pico-hydraulic tailored turbine design: a novel approach using a dimensionless design chart

Energy consumed by the water industry is not negligible and improvements on energy efficiency in water distribution networks are still needed. This work aims to provide a new approach to design tailored torpedo shaped in-pipe axial pico-hydraulic turbines for the recovery of energy in water distribution networks. Simple straight untwisted blades with arc of circles profiles are imposed to simplify manufacturing. Ideal flow bi-dimensional cascade theory with Weinel isolated airfoil to cascade correlations are used as compromise between accuracy and simplicity. From it, a dimensionless design chart is build. A novel flow-to-head factor is chosen as main dimensionless factor to simplify stator analysis and obtain a more compact chart. From five usual input design parameters, choosing the value of three, and letting two of them to vary allows the trace of a space of all optimal designs. From this space, a turbine or family of turbines can be obtained. A design example on the same conditions as a experimentally tested turbine found in the literature was carried over and simulated with OpenFOAM open source library. A mesh parametric study for numerical validation purposes is realized. Discretization uncertainty found for the selected mesh was about one point for the hydraulic efficiency. The designed and simulated turbine showed a maximum hydraulic efficiency of . The presented non-dimensional approach proved to be useful to design efficient tailored simple pico-hydraulic turbines for energy recovery in distribution water networks, relaying on one design chart.This work have been supported by Fundación Séneca (Murcia, Spain)[Grant No. 20352/FPI/17]

Numerical studies on laminar, transitional and turbulent convective airflows in channels with generalised geometry, including applications to thermal-ventilation passive systems

The flows induced by natural convection appear in many engineering problems. Configurations formed by heated plates where these processes occur, were the topic of intense study in past years. However, new systems with a different constructive disposition and applications in several fields (bioclimatic architecture, electronic cooling, nuclear energy cooling systems) are at the moment of great interest. Since typical applications of buoyancy-driven airflows in smooth vertical channels are usually in small-scale devices (i.e. in electronic cooling equipment), most investigations were carried out for laminar flows. As a consequence of the great scale of certain passive ventilation systems, as solar chimneys, Trombe walls, or roof collectors, the flow established becomes transitional or even fully turbulent. The regarded geometries frequently involve structures based on converging and sloped channels formed by heated plates, where buoyancy-driven flows take place. Therefore, the study of problems such as the transition to turbulent regime or flows with walled-channel geometries including sloped and converging walls are key to assertively find out the real heating transmission existing in these new systems in a more realistic manner. Nowadays, the need to achieve human comfort by passive heating and ventilation techniques is greater as is the requirement for energy saving. Passive solar systems are the basic elements of bioclimatic design and they do not involve the use of mechanical or electrical devices. The Trombe Wall is the primary example of the technique called indirect gain, whose typical configuration is usually formed by a thick, darkened, masonry wall and a glazed wall. In ventilation applications, other passive systems, called thermosyphons, heat syphons or solar chimneys, can yield natural motions of air due to the induced temperature differences by solar heating. Although several reported works provided useful results for the analysis and design of passive solar devices in buildings, these works cannot determine the necessary details of convection for numerical simulations. Furthermore, as an important lack of design correlations is detected, it is necessary to carry out a systematic study that supplied the heat transfer coefficient and the mass-flow rate as a function of relevant parameters, for several configurations

Numerical analysis of the vacuum infusion process for sandwich composites with perforated core and different fiber orientations.

The vacuum infusion is a process usually applied to manufacture large structures of composite materials, such as wind turbine blades. The specific stiffness and weight ratio required by these structures can be achieved by manufacturing sandwich composites. The forecast by numerical simulation of the resin infusion flow is an indispensable tool to design and optimize the manufacturing process of composite. Present work analyzes by numerical simulation the mold filling process of a sandwich composites, performed by fiberglass plies with different fiber orientations and a perforated core. The flow through a single perforation of the core is analyzed and the influence of the permeability values of fiberglass on the volume flow through core perforations is determined. In order to reduce the computing costs, a transfer function to simulate the flow through the perforations is developed and integrated in the numerical code by computational subroutines. A 3D numerical modeling of a sandwich composite, in which the flow through the core perforations is simulated via computational subroutines, is carried out and experimentally validated.The research work presented in this paper has been carried out under the project "Automation of the global manufacturing process for wind turbine blades (AQ–BLADE)" IDI‐20110154, financially supported by Centro para el Desarrollo Tecnológico Industrial (CDTI) from the Spanish Government

Numerical anlysis of the vacuum infusion process for laminated composites with different fiber orientations.

The vacuum infusion (VI) is a process usually applied to manufacture large structures of composite materials, such as wind turbine blades. Present work analyzes the macroscopic resin ow through a laminate of fiberglass plies with different orientations, during the filling stage of the VI process to manufacture two different pieces. The pressure inside the mold, velocity vectors and the resin inlet mass flow are studied through a 3D numerical modeling under non-steady conditions validated experimentally. The numerical model simulates each ply of the laminate like an individual porous media and takes into account the stacking sequence of the laminate. The influence of the permeability values of the distribution media and the fiberglass laminate on the evolution of resin infusion is analyzed. The numerical model reproduces the effects of the stacking sequence and race-tracking on the resin flow front.The research work presented in this paper has been carried out under the project "Automation of the global manufacturing process for wind turbine blades (AQ{BLADE)" IDI{20110154, nancially supported by Centro para el Desarrollo Tecn ologico Industrial (CDTI) from the Spanish Government

Modelización numérica del proceso de transferencia de calor, del flujo convectivo inducido y de la potencia generada en una central eólico solar. Póster

La chimenea eólico solar tiene por objeto producir energía eléctrica a partir de la energía del sol. La radiación solar incide sobre el colector que, a modo de invernadero, calienta el aire que hay en su interior. El aire caliente asciende por flotación a través de la chimenea, accionando y haciendo girar mediante este movimiento ascendente la turbina que se encuentra en la base de la chimenea. Esta turbina se conecta a un generador eléctrico que produce la corriente. El sistema está formado por un colector con forma cónica de radio de base 122 m, y altura en el centro y los extremos 6 y 2 m respectivamente, una chimenea en el centro del colector de 194,6 m de altura y 5 m de radio, y una turbina de 4 álabes y 5 m de radio girando a 100 rpm. En este trabajo se ha desarrollado un modelo numérico de los flujos convectivos inducidos por flotación dentro de la chimenea solar

Sistema integrado de desalación por energías renovables sin emisión de salmuera

Los efectos medioambientales son uno de los principales problemas de las instalaciones de desalación de agua de modo masivo. Para alcanzar el objetivo ideal de evitar la descarga de salmuera de rechazo en la desalación de agua de mar, la sal debe ser completamente separada del agua, obteniéndola como un producto secundario de valor económico. Si además no se desea aumentar las emisiones de CO2, la energía necesaria debe extraerse de una combinación de fuentes renovables. Este trabajo presenta un análisis de un esquema integrado de desalación consistente en dos subsistemas secuenciales: una planta de destilación multiefecto (MED) y un ciclo evaporativo por compresión mecánica de vapor (CMV). La energía se obtiene de varias turbinas eólicas y de un campo de colectores solares. El sistema diseñado produce 100 m3/h de agua dulce con total separación de la sal y el agua. El consumo energético estimado es de 2.362 Kwt-h por el sistema MED y 1.944 Kwe-h por el CMV. Al utilizar energías renovables la reducción de emisiones de CO2 a la atmósfera al año es de 8.957 Tn debidas al consumo eléctrico y 6.584 Tn al consumo térmico. Se ha realizado un estudio preliminar de la inversión, la amortización y los costes de explotación del sistema completo. Teniendo en cuenta los precios de la venta de la energía producida y de la sal, el precio del agua sería de 0,59 €/m3. Con una subvención inicial del 35%, se podría reducir a 0,41 €/m3

Energy optimization of air conditioning system using hydrosolar roof as heat sink

An environmentally friendly alternative device, called Hydrosolar Roof, designed for heat dissipation in buildings has been necessary to include all the elements in a global model. Then, three main subsystems have been considered: Cooling Machine, Hydraulic Network and Hydrosolar Roof. A description of the three subsystem is done and the mathematical model is presented.The Cooling machine thermodynamic model has been carried out using EES (Engineering Equation Solver). The Hydraulic network model has piping, pump and nozzle information. The Hydrosolar Roof direct contact heat and mass transfer simulation has been development with a CFD code. Special attention has been paid on the cooling efficiency. The global model has been applied to a real prototype facility experimentally tested. All the energy consumptions have been calculated for different pumping heads. A global coefficient of performance (COP) has been defined and the optimum value obtained.The authors wish to acknowledge the collaboration in the calculations of A. Navarro, as well as José María Galán, Energy, Comfort and Enviroment S.L. Manager, as the proporser of the original idea

Prediction of the lifetime of droplets emitted from mechanical cooling towers by numerical investigation

A numerical modelling capable to simulate the drift and the evaporation of water droplets emitted by a mechanical cooling tower in an urban area is presented. The model is based on a real mechanical draft cooling tower situated in the surroundings of the Miguel Hernández University (Elche, Spain). An experimental study of the deposition of droplets from the cooling tower is done in order to validate the numerical modelling. This study is performed by means of the water sensitive papers technique. A biharmonic interpolation is used for obtaining the total deposition on the floor. A total of 14 cases, everyone with different atmospheric conditions, have been simulated and experimentally validated. An analytical model for the droplets lifetime prediction is validated with the results obtained from the numerical modelling. The present study shows the influence of the atmospheric and droplets conditions in the droplets lifetime, providing useful information to analyse the spread of contaminants or bacteria inside the droplets released from the cooling tower.This research is sponsored by the Spanish Government, through the Projects No. ENE2013-48696-C2-2-R and ENE2013-48696-C2-1-R, including FEDER (European Union

Water drop size numerical optimization for hydrosolar roof

Air-conditioning systems of buildings and other industrial facilities commonly use water as a heat drain to remove heat from refrigerant condensers. Classical solutions to reduce the temperature of this service water are air cooled heat exchangers or mechanical draught cooling towers. The Hydrosolar Roof optimized in this paper, working as a heat focus in the thermodynamic cycle of a heat pump, achieves the same objectives without fan energy consump tion. This system consists of an extended framework on the roof of the building with some thermal plates installed over it. Some of the plates are made of a high reflective material, and the others are made of absorbent material. The Hydrosolar Roof uses the design of the reflective and absorbent parts of the device, made of flat plates, to form a sloping channel. Solar radiation is collected by this channel and, due to local heating in this zone, natural convection through it is produced. The natural induced air flow is irrigated with water sprays, placed below the plates at the inlet of the channel, generating a cross flow between air and water. In this way, water is cooled by direct contact with a reduced amount of vaporization, and most of the water is recovered at a reduced temperature. This work shows the numerical study to obtain an optimum for the sprayed water drop size. The two-dimensional version of the CFD code Fluent was applied to predict both atmospheric air and sprayed water main variables in a real geometry and under different thermodynamic conditions.The authors wish to acknowledge the collaboration in the calculations of A. Navarro, as well as José María Galán, Energy, Comfort and Environment S.L. manager, as proposer of the original idea