Search results for " Gradient"
showing 10 items of 575 documents
Towards the first proof of the concept of a Reverse ElectroDialysis - Membrane Distillation Heat Engine
2019
Abstract The coupling of Reverse Electrodialysis with Membrane Distillation is a promising option for the conversion of waste heat into electricity. This study evaluates the performances of the integrated system under different operating conditions, employing validated model and correlations. This work provides a detailed description of the behaviour of a real RED-MD heat engine and indicates the set of inlet concentrations, velocities and equipment size which returns the highest cycle exergy efficiency. These operating conditions were selected for the pilot plant developed within the EU-funded project RED Heat to Power. For the first time, a perspective analysis was also included, consider…
Thermolytic reverse electrodialysis heat engine: model development, integration and performance analysis
2019
Abstract Salinity gradient heat engines represent an innovative and promising way to convert low-grade heat into electricity by employing salinity gradient technology in a closed-loop configuration. Among the aqueous solutions which can be used as working fluid, ammonium bicarbonate-water solutions appear very promising due to their capability to decompose at low temperature. In this work, an experimentally validated model for a reverse electrodialysis heat engine fed with ammonium bicarbonate-water solutions was developed. The model consists of two validated sub-models purposely integrated, one for the reverse electrodialysis unit and the other for the stripping/absorption regeneration uni…
Soret coefficient of trace ions determined with electrochemical impedance spectroscopy in a thin cell. Theory and measurement
2018
The tendency of a substance to migrate due to a temperature gradient is known as thermodiffusion or the Soret effect. We believe that this is the first work that describes the study of the Soret effect using electrochemical impedance spectroscopy in a non-isothermal thin cell, and shows how the Soret coefficient can be determined from these measurements. The effect of a temperature gradient in a thin cell is analyzed, both theoretically and experimentally. Our theoretical modeling of the system predicts the effect of key parameters to the impedance spectra. Experimentally we determine the Soret coefficient of the redox couple Fe(CN)64−/Fe(CN)63− in an aqueous KCl solution. It is found that …
The Performance of the Gradient-Like Influence Measure in Generalized Linear Mixed Models
2015
A gradient-like statistic, recently introduced as an influence measure, has been proven to work well in large sample, thanks to its asymptotic properties. In this work, through small-scale simulation schemes, the performance of such a diagnostic measure is further investigated in terms of concordance with the main influence measures used for outlier identification. The simulation studies are performed by using generalized linear mixed models (GLMMs).
Energy harvesting by waste acid/base neutralization via bipolar membrane reverse electrodialysis
2020
Bipolar Membrane Reverse Electrodialysis (BMRED) can be used to produce electricity exploiting acid-base neutralization, thus representing a valuable route in reusing waste streams. The present work investigates the performance of a lab-scale BMRED module under several operating conditions. By feeding the stack with 1 M HCl and NaOH streams, a maximum power density of ~17 W m−2 was obtained at 100 A m−2 with a 10-triplet stack with a flow velocity of 1 cm s−1, while an energy density of ~10 kWh m−3 acid could be extracted by a complete neutralization. Parasitic currents along feed and drain manifolds significantly affected the performance of the stack when equipped with a higher number of t…
Effect of different aqueous solutions of pure salts and salt mixtures in reverse electrodialysis systems for closed-loop applications
2018
Abstract Reverse Electrodialysis (RED) in a closed-loop arrangement is a viable way to convert low-grade heat into electric power. The present work experimentally investigates the use of pure salt- and equimolar two salts-water solutions as feeds in a lab-scale RED unit. RED performances were analysed in terms of Open Circuit Voltage (OCV), stack resistance and corrected power density. The pure salts and the mixtures employed were chosen via a computational analysis. Effect of feed solution velocity and concentration was investigated. Results concerning the pure salt-water experiments show that NH4Cl is the most performing salt in the concentration range probed, while higher power density v…
An Image Segmentation Algorithm based on Community Detection
2016
International audience; With the recent advances in complex networks, image segmentation becomes one of the most appropriate application areas. In this context, we propose in this paper a new perspective of image segmentation by applying two efficient community detection algorithms. By considering regions as communities, these methods can give an over-segmented image that has many small regions. So, the proposed algorithms are improved to automatically merge those neighboring regions agglomerative to achieve the highest modularity/stability. To produce sizable regions and detect homogeneous communities, we use the combination of a feature based on the Histogram of Oriented Gradients of the …
Definition of a mutual reference shape based on information theory and active contours
2013
In this paper, we propose to consider the estimation of a reference shape from a set of different segmentation results using both active contours and information theory. The reference shape is then defined as the minimum of a criterion that benefits from both the mutual information and the joint entropy of the input segmentations. This energy criterion is here justified using similarities between information theory quantities and area measures, and presented in a continuous variational framework. This framework brings out some interesting evaluation measures such as the specificity and sensitivity. In order to solve this shape optimization problem, shape derivatives are computed for each te…
Elaboration de matériaux à gradient de propriétés fonctionnelles pour les composants face au plasma des machines de fusion thermonucléaires
2014
The objective of this study was to develop a Functionally Graded Material (FGM) W / Cu to replace the compliance layer (Cu-OFHC) in the plasma facing components of thermonuclear fusion reactor like ITER. The peculiarity of this work is to elaborate these materials without exceeding the melting temperature of copper in order to control its microstructure. The co-sintering is the most attractive solution to achieve this goal.The first phase of this study has been to decrease the sintering temperature of the tungsten to achieve this co-sintering. The elaboration of a Functionally Graded Materials being delicate, thermo-mechanical calculations were performed in order to determine the number and…
Mapping spatial patterns of denitrifiers for bridging community ecology and microbial processes along environmental gradients
2009
International audience; While there is ample evidence that microbial processes can exhibit large variations at a field scale, very little is known about the spatial distribution of the communities mediating these processes. The objective of this study was to explore spatial patterns of size and activity of the denitrifying community, a functional guild involved in N-cycling, in a grassland field subjected to different cattle grazing regimes. We used geostatistical modeling to map the distribution of size and activity of the denitrifier community in the pasture. Size of the denitrifier community was estimated by PCR quantification of the denitrification gene copy numbers while its activity w…