About
109
Publications
22,534
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,916
Citations
Introduction
Additional affiliations
June 2000 - July 2001
September 1995 - March 2003
Publications
Publications (109)
Rapid water filtration with pressurised porous media filters is extensively applied in drip irrigation systems. In double-chamber filters, the underdrains are fixed to the base of the inner plate to sustain the media above while draining water. Here, a new underdrain design intended to reduce the filter energy consumption is presented. The main dif...
Pressurised sand filters used in drip irrigation need periodic backwashing to flush the contaminant particles out of the porous media. This process consumes high amounts of energy and water. The selection of more efficient backwashing operational conditions requires accurate information of the pressure drop and the bed expansion, the latter being n...
Sand media filters are especially recommended to prevent emitter clogging with loaded irrigation waters, but their performances rely on backwashing. Despite backwashing being a basic procedure needed to restore the initial filtration capacity, there is a lack of information about the solid removal efficiency along the media bed depth. An experiment...
In micro-irrigation systems, distinct media filters and filtering materials are employed to remove suspended solids from irrigation water and thereby avoid emitter obstruction. Turbidity is related to suspended solids and dissolved oxygen depends on organic matter load. At this time, no models exist that are trustworthy enough to forecast the disso...
Rapid deep bed filtration is a common process of drip irrigation systems to prevent emitter clogging. The particle retention in the porous media increases the pressure difference between the filter's inlet and outlet. Commercial operational instructions preset a threshold value of this pressure difference to define the end of a filtration cycle. Ac...
Accurate model predictions are fundamental when designing porous media filters in drip irrigation systems that reduce both energy and water consumption. Many studies have focused on improving filter hydraulics under clean water conditions but further advances may require consideration of particle retention by the granular media. Rapid deep bed filt...
Pressurized sand media filters are commonly used in drip irrigation systems to prevent emitter clogging. However, the performance of these filters may be improved with more information about the retention of solids at different bed depths under different filter operation conditions and irrigation water sources. In this study, experiments in a scale...
Thermoelectric generators (TEGs) often use plate-fin heat sinks as cold side heat exchangers under forced convection. The available net electrical power obtained from these TEGs corresponds to that generated (Seebeck effect) minus that consumed (cooling fan). Generation and self-consumption have different trends as a function of the air flow speed,...
Actions for improving the energy efficiency of pressurised porous media filters used in drip micro-irrigation require methods to properly determine the behaviour of both filtration and backwashing modes. The latter is essentially a fluidisation process. Though many authors have analysed fluidised bed columns, very few studies have dealt with the ba...
The popularity of small wind turbines would rise in future, because of electricity prices are still growing. Next generation of small wind-turbines can have higher efficiency values. Under wind gusts and turbulences, the system should be very sensitive to wind conditions. In this work, it is presented a control system that can improve the performan...
Irrigation is very important for global food production and, therefore, it is key to moving towards increasingly sustainable irrigation systems. However, the adoption of more efficient water-use techniques, such as drip irrigation, increases energy consumption. A large part of the efficiency of drip irrigation systems depends on the equipment used,...
Highlights
An outlet pipe with twice the cross-sectional area reduced the filter pressure drop by 12%.
Two-outlet designs did not improve the hydraulic performance of the central wand.
Flow uniformity in the sand bed was improved with a central downward outlet pipe.
Abstract . The pressurized sand filters used in drip irrigation systems have three...
Selective Catalytic Reduction systems (SCR) are very efficient on reducing NOx. However, they only perform properly when exhaust gas temperature is higher than 180 °C. This means that for low engine regimes combined with cold engine temperatures, SCR systems remains inactive.
This study presents a new approach to minimize the amount of NOx emitted...
This study presents a new approach to minimize the amount of NOx emitted by diesel engines of Heavy-Duty Vehicles during low engine regimes and low gases temperature conditions. We propose the addition of an electric Exhaust Gas Heater (EGH) to make the SCR system inject the urea solution at low engine regimes. The second part of this study focuses...
The installed power capacity from small wind turbines would rise in case of having higher efficiency values. The performance of these devices is very sensitive to wind conditions, especially to wind gusts and turbulence. Performance extracted from small-scale wind turbine datasheets show large variations of power output between turbulent and non-tu...
The small open area available at the slots of underdrains in pressurized granular bed filters for drip irrigation implies: (1) the existence of a region with non-uniform flow, and (2) local values of modified particle Reynolds number >500. These flow conditions may disagree with those accepted as valid for common pressure drop-flow rate correlation...
Automotive thermoelectric generators (ATEGs) are devices used to harvest waste energy from the exhaust gases of internal combustion engines. An ATEG is essentially formed by three main elements: (1) heat absorber in contact with exhaust gases; (2) thermoelectric modules that directly convert heat into electricity; (3) heat sink to increase the heat...
Commercial sand media filters adopt different underdrain designs, with pod, wand and spike designs being the most common. Studies about the consequences of using these configurations are often not conclusive since auxiliary elements and dimensions vary between filters. Here computational fluid dynamics (CFD) simulations were carried out comparing u...
Solar thermoelectric generators (STEGs) are a promising technology to harvest energy for off-grid applications. A wide variety of STEG designs have been proposed with the aim of providing non-intermittent electrical generation. Here, we designed and tested a STEG 0.5 m long formed by nine commercial thermoelectric generator modules and located at g...
Plate-fin heat sinks under forced convection are economical dissipaters employed in a wide variety of sectors. These types of heat sinks are commonly used in power generation by means of commercial thermoelectric generator modules. The design of the heat sink is a key factor in these power generation systems since it greatly affects the efficiency...
Sand media filtration is frequently used in drip irrigation systems. Commercial filter designs may use different underdrain models but wand-type designs provide a large ratio of horizontal area covered by underdrains and are expected to provide a uniform flow of water through the medium. The complexity of these designs makes it difficult to analyse...
Low exhaust gas temperatures of internal combustion engines, resulting from cold-starts, low loads or low temperature ambient conditions, can compromise the performance of the automotive aftertreatment system. In this situation, the engine is running far from its design point, with a very low performance of the catalytic converter since it has not...
Education is a keyword when environmental sustainability and climate change mitigation are pursued. It is a global objective that affect all the World, so social and technological universities are engaged with the aim of mitigating the change and improving the necessary adaptation. From the technical school of the University of Girona, our educatio...
Voltage sag is one of the most considerable problems in power distribution system. In this work the performance study of the FACTS family; i.e. the distributed compensator (D STATCOM), dynamic voltage restorer (DVR), and pulse width modulation (PWM) switched auto-transformer, is carried out, with regard to the number of switching devices and the va...
Purpose
This paper aims to report on a case study concerning the development of sustainable energy partnerships involving engineering faculty and undergraduate students at the University of Girona, Catalonia, Spain.
Design/methodology/approach
Faculty were motivated to seek partnerships with public and private entities in the local area for the pu...
Automotive thermoelectric generators (ATEG) have become a promising technology for exhaust heat recovering in vehicles. Many models and prototypes have been developed and validated with very promising results. Most of them have been analysed in both steady-state and transient conditions in engine test benches. However, only a few have been tested o...
Automotive thermoelectric generators (ATEG) have become a promising technology for exhaust heat recovering in vehicles. Many models and prototypes have been developed and validated with very encouraging results. Most of them have been analyzed in both steady-state and transient conditions in engine test benches. However, only very few have been tes...
The need for more sustainable mobility promoted research into the use of waste heat to reduce emissions and fuel consumption. As such, thermoelectric generation is a promising technique thanks to its robustness and simplicity. Automotive thermoelectric generators (ATEGs) are installed in the tailpipe and convert heat directly into electricity. Prev...
The need to reduce both energy consumption and greenhouse gas emissions has boosted the interest in using thermoelectric generators (TEGs) as waste heat energy harvesters. High-power TEGs are usually formed by an array of commercial thermoelectric modules (TEMs). Recent studies have analyzed the effects of using different types of electrical connec...
Recent developments of high performance thermoelectric (TE) materials have increased the interest of using this technology to directly convert waste heat into electricity. In the automotive sector, many automotive thermoelectric generators (ATEGs) designs use TE modules (TEMs) with high hot side temperatures to cope with high engine load regimes. H...
Reduction of pressure drop across sand media filters-which are broadly used for preventing emitter clogging-should help reducing energy consumption in microrrigation systems. Previous research has shown that most of the pressure drop is located at sand filter underdrain. In this work, the effect of the nozzle geometry on the pressure drop of a sand...
For the widespread application of thermoelectric generators, it is of vital importance to have convenient simulation tools in order to test the behavioral consequences of a thermoelectric generator in almost real conditions. The simulation by numerical methods of the performance of automotive thermoelectric generators (ATEG) allows for time- and co...
Static Series Compensator (SSC) is a power electronic based device that provides three-phase controllable voltage source to restore the load voltage to pre-sag conditions within few milliseconds. This paper proposes a new control technique based on an adaptive tunning PI controller that uses a selective controller to describe the effectiveness of S...
This paper deals with the problems of improving power quality in electrical power grids by using multiple FACTS devices like STATCOM, SSSC and UPFC. The present scenario will focus on the working of the various FACTS family under different types of generator faults that can cause any other transmission lines to be overflowed. The simulation analysi...
The technological advancements in wind energy conversion have led to increased wind power generation in recent years. Static synchronous compensator (STATCOM) is used extensively in power systems due to its ability of providing the flexible power flow control. The main motivation for choosing STATCOM in wind farms is that it can provide bus bar sys...
The feasibility of using crossflow runners as single rotors in vertical-axis wind turbines (VAWT) or as blades in horizontal-axis wind turbines (HAWT) is numerically studied. A computational fluid dynamics model is validated from data obtained in a wind tunnel. Three crossflow runners with different number of blades are tested. Values of drag, lift...
Thermoelectric generators (TEGs) have become a promising technology for vehicle exhaust heat recovery. Many models and prototypes have been developed and validated with very promising results. The majority of them have been tested under steady-state engine conditions. However, light-duty vehicles operate under wide variable loads, causing significa...
This work improves the accuracy of longitudinal thermoelectric energy harvesting (LTEH) models introducing the prediction of the interconnection effects. LTEHs are composed of multiple arrays of thermoelectric generators (TEG) electrically arranged in series-parallel configuration. The way that TEG modules are connected strongly affects the electro...
Small wind turbines are commonly single-turbine installations owned by individual homeowners or farmers for on-site electricity consumption, and are becoming an attractive alternative for off-grid electrification and water pumping, both as stand-alone applications and in combination with other energy technologies such as photovoltaic, small hydro o...
The effect of the nozzle geometry on the pressure drop of a sand filter was experimentally studied. Four nozzles were analysed: one commercially produced with a conical shape and three alternative cylindrical underdrains that differed in the location and the number of slots. Experiments in both filtration mode and backwashing conditions for a wide...
Microirrigation is an irrigation technology with high potential water use efficiency. For preventing emitter clogging, which reduces the uniformity and can lead to inoperability of microirrigation systems, filtration is mandatory. Sand media filters are broadly used to protect microirrigation systems, but their manufacturer’s pressure requirements...
Traditional waterwheels are widely used in remote areas as a source of mechanical energy for grinding grain. The classical design suffers of a very low hydraulic efficiency. The basic challenge is to increase the power output but not the rpms, with a desirable working regime in the range of 120-160 rpm. We study the hydraulic efficiency of waterwhe...
Energy consumption in pressurised irrigation systems has become a major issue, even when microirrigation is used. Although the emitters used in microirrigation operate at low pressures, their filters require higher pressures and there is therefore no reduction in energy consumption. Part of the pressure drop found in filters is produced by the poro...
Filtration is necessary for avoiding emitter clogging in micro irrigation systems. The pressure drop across different granular media, such as silica sand, crushed recycled glass, surface modified glass and glass microspheres of selected grain sizes ranging from 0.63 to 1.50 mm, was studied in a laboratory filter scaled from a commercial filter usin...
We experimentally burn thin solid fuels and obtain the speed of the flame front when it propagates (1) within a narrow channel (closed cross section), (2) within a channel with lateral walls only and (3) through a free cross section (plain case). The latter configuration is the classical one and it has been extensively studied with analytical, nume...
Sand filters are frequently used in micro-irrigation especially when water contains large amounts of organic contaminants. This type of filter has the advantage of its simplicity and that the main filtration mechanism is based on depth filtration, giving an additional removal capacity in comparison with screen or disc filters, which essentially wor...
Magnus wind turbine uses rotating cylinders instead of conventional horizontal axis blades. These cylinders rotate around their own axes and create a rotational force according to Magnus effect. Although this kind of wind turbines have many benefits over conventional axis blades and can exhibit different blade characteristics, it is not clearly dem...
We analyze the flame front speed in the downward combustion of multiple parallel samples of thermally thin fuels at normal gravity and far from extinction conditions. In contrast with the single sample case, where conduction through the gas-phase is the dominant heat transfer mechanism, in the multiple parallel samples case, radiative heat fluxes m...
In fluid mechanics courses of engineering curricula, theoretical performance curves of hydraulic turbines are obtained by means of simple analytical expressions that tend to overestimate experimental data. As we show here in the analysis of a laboratory-scale Pelton wheel, a much deeper physical insight can be achieved by means of general-purpose c...
We focus on the front propagation of diffusive flames obtained from the downward burning of inclined thermally thin solid fuels. This process consists of a pyrolysis reaction in the solid-phase and a combustion reaction in the gas phase. The solid-phase model is based on two coupled one-dimensional equations of temperature and solid density. We red...
The prediction of the pressure drop produced by sand media filters in clean condition has a practical interest as it will define the amount of head loss available for the retention process. The underdrain system in a sand filter is crucial to allow the water flow through the sand media preventing sand losses within the filtered water. However an im...
Sand filters are commonly used to protect drip irrigation systems especially when large amounts of organic contaminants are present. Moreover sand filters have the advantage of simplicity and large capacities in comparison with other types of filters.The main objectives of this paper are firstly to develop an analytical equation to calculate the to...
We derive a new analytical expression for the flame front speed in the downward combustion of thin solid fuels based on a model that consists of a preheating region plus a pyrolyzing one. The solid phase is modeled by means of a simple but physically realistic behavior of the main variables in these two regions, whereas the gas phase follows classi...
A comparison between the downward flame spread rate for thermally thin samples with one or two inhibited edges is done in multiple situations. The effects of atmospheric composition as well as the width and thickness of a cellulosic-type fuel are tested experimentally. We have found that the normal velocity to the inclined flame front in a side-edg...
For the Neolithic transition in the Near East and Europe, this paper compares the isochrones predicted by computational models to those obtained by interpolating the archaeological data. This comparison reveals that there is a major inconsistency between the predictions of the models
and the archaeological data: according to the models, the Neolith...
De Ris formulae for the flame spread rate over solid fuels that propagate against an external fluid flow for both the thermally thin and thick regimes have become well-known. In some cases, it is expected that predictions from these formulae will fail since they are independent of parameters that may modify the burning velocity. Based on the techni...
We derive analytical expressions for the propagation speed of downward combustion fronts of thin solid fuels with a background flow initially at rest. The classical combustion model for thin solid fuels that consists of five coupled reaction-convection-diffusion equations is here reduced into a single equation with the gas temperature as the single...
It is often assumed that total head losses in a sand filter are solely due to the filtration media and that there are analytical solutions, such as the Ergun equation, to compute them. However, total head losses are also due to auxiliary elements (inlet and outlet pipes and filter nozzles), which produce undesirable head losses because they increas...
Slow-rotating waterwheels are mechanical devices of great historical relevance since they provided power to ancient communities for shifting from a subsistence to a market-oriented economy. Technical studies of these antecessors of hydraulic turbines mainly rely on basic principles that do not take into account the blade-to-blade distance and, ther...
Slow rotating waterwheels have been recently proposed as affordable sources of renewable energy in rural areas. In terms of hydraulic efficiency, classical horizontal waterwheels reach values on the order of 50%, being well below those obtained from overshot (71%), waterfall (66%) and, even, undershot (65%) vertical ones. Based on the study of an h...
Here we analyze the hydraulic performance of an ancient Spanish horizontal watermill. Previous studies of similar devices have focused on qualitative descriptions of their technical functioning, providing efficiency curves based on two-dimensional analytical approximations. In contrast, here we perform three-dimensional computational fluid dynamics...
We derive new expressions to estimate the burning velocity of a laminar gas flame in a simplified combustion model based on a one-step single reaction with transport coefficients (mass and heat) depending on temperature, and species with different specific heats. These new expressions generalize the bounds and approximations previously derived by W...
For a massless fluid (density = 0), the steady flow along a duct is governed exclusively by viscous losses. In this paper, we show that the velocity profile obtained in this limit can be used to calculate the pressure drop up to the first order in density. This method has been applied to the particular case of a duct, defined by two plane-parallel...
We review the progress in the field of front propagation in recent years. We survey many physical, biophysical and cross-disciplinary applications, including reduced-variable models of combustion flames, Reid's paradox of rapid forest range expansions, the European colonization of North America during the 19th century, the Neolithic transition in E...
In this paper we present the structural and magnetic analysis of a nanocrystalline Fe75Nb10Si5B10 alloy produced by mechanical alloying. The effects of milling time on microstructure, thermal behavior and magnetic properties were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and vibrating sample magnetometry (VSM). By...
In this paper we analyze the speed of gas flames in a combustion premixed model that consists of two species (fuel and non-fuel). The main novelty with respect to recently published papers is that here we take into account the effect of the diffusion velocities in the energy equation. This means that the speed of the traveling wave obtained by nume...
We generalize a previous model of time-delayed reaction–diffusion fronts (Fort and Méndez 1999 Phys. Rev. Lett. 82 867) to allow for a bias in the microscopic random walk of particles or individuals. We also present a second model which takes the time order of events (diffusion and reproduction) into account. As an example, we apply them to the hum...
The second differential of the entropy is used for analysing the stability of a thermodynamic climatic model. A delay time for the heat flux is introduced whereby it becomes an independent variable. Two different expressions for the second differential of the entropy are used: one follows classical irreversible thermodynamics theory; the second is...
We investigate the consequences of Darwinian selection in a daisymodel with uniform temperature, inter-specific competition and multiple daisies. The assumption of a higher competition between species than within them allows for the coexistence of more than two species in equilibrium. Thus, it is the first time that a high biodiversity with equal e...
Here I develop a model of a radiative–convective atmosphere with both radiative and convective schemes highly simplified. The atmospheric absorption of radiation at selective wavelengths makes use of constant mass absorption coefficients in finite width spectral bands. The convective regime is introduced by using a prescribed lapse rate in the trop...
The wave-of-advance model has been previously applied to Neolithic human range expansions, yielding good agreement to the speeds inferred from archaeological data. Here, we apply it for the first time to Palaeolithic human expansions by using reproduction and mobility parameters appropriate to hunter-gatherers (instead of the corresponding values f...
Convection reduces greenhouse effect by transporting a certain amount of non-radiative dynamic energy to the upper atmosphere, where this energy dissipates and radiates into space without interaction with greenhouse substances in the lower atmosphere. In this paper we show that the height of the convective layer z<sub>c</sub> is finite and independ...
The long-term mean properties of the global climate system and those of turbulent fluid systems are reviewed from a thermodynamic viewpoint. Two general expressions are derived for a rate of entropy production due to thermal and viscous dissipation (turbulent dissipation) in a fluid system. It is shown with these expressions that maximum entropy pr...
We model the wavelength-dependent absorption of atmospheric gases by assuming constant mass absorption coefficients in finite-width spectral bands. Such a semigray atmosphere is analytically solved by a discrete ordinate method. The general solution is analyzed for a water vapor saturated atmosphere that also contains a carbon dioxide-like absorbin...
The hypothesis that the steady state of the climate is constrained to maximize its dissipation is investigated by using a one-dimensional radiative-convective model where the convective fluxes are parameterized following the mixing length theory. The eddy heat diffusivity is chosen to produce the maximum energy dissipation caused by convection (max...
The evolution of the speed of wavefronts for reaction–diffusion equations with time-varying parameters is analysed. We make use of singular perturbative analysis to study the temporal evolution of the speed for pushed fronts. The analogy with Hamilton–Jacobi dynamics allows us to consider the problem for pulled fronts, which is described by Kolmogo...
The effect of initial conditions on the speed of propagating fronts in reaction-diffusion equations is examined in the framework of the Hamilton-Jacobi theory. We study the transition between quenched and nonquenched fronts both analytically and numerically for parabolic and hyperbolic reaction diffusion. Nonhomogeneous media are also analyzed and...