Special Issue "Blue Energy"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (30 October 2020).

Special Issue Editors

Prof. Dr. Svetlozar G. Velizarov
Website
Guest Editor
Laboratory for Green Chemistry (LAQV), Faculty of Science and Technology, New University of Lisbon, 2829-516 Caparica, Portugal
Interests: clean (mainly membrane-assisted) (bio)chemical processes and technologies; electro-membrane processes; water treatment, sustainable salinity gradient-based (“blue”) energy generation and/or storage
Special Issues and Collections in MDPI journals
Dr. Andrea Cipollina
Website
Guest Editor
Chemical Process and Plant Design at the Engineering Department, University of Palermo, Palermo, PA, Italy
Interests: Salinity gradient power (SGP) processes; water technologies, Computer-aided process modelling and optimisation; fluid flow characterization and prototype design, commissioning and operation; water treatment; brine re-use

Special Issue Information

Salinity gradient power (SGP) technologies nowadays represent novel and promising alternative sources of sustainable energy, obtainable from the controlled mixing of solutions with different salinities. Significant research efforts have been devoted to demonstrating the technological advances of already-proven technologies, such as reverse electrodialysis, pressure-retarded osmosis, capacitive mixing, as well as developing new (often hybrid) emerging processes. Research activities have spanned from fundamental theoretical analysis to the development of novel materials and from process modelling and optimisation to the demonstration of adequate technological feasibility/readiness levels through commissioning of the first pilot plants, operating in real environments, thus reaching the interest of a wider audience, including academics, industries and public authorities operating in the field of sustainable energy sources. This Special Issue will open the floor to introducing the most recent research activities carried out in the field of SGP technologies. The goal is to provide a shared knowledge platform, on which relevant advances are presented to the scientific and technological communities, with the hope of providing a robust and wide spectrum reference, thus acting as a stepping-stone for the future practical implementation of these new technologies.

Keywords

  • sustainable energy
  • mixing entropy
  • salinity gradient power
  • energy from sea and saline brines
  • energy from wastewaters
  • reverse electrodialysis
  • ion-exchange membranes
  • pressure retarded osmosis
  • osmotic membranes
  • capacitive mixing
  • flow batteries
  • (bio)fuel cells
  • mechanistic process modelling
  • multivariate statistical modelling
  • CFD simulations

Published Papers (5 papers)

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Research

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Open AccessArticle
The Effect of the NaCl Bulk Concentration on the Resistance of Ion Exchange Membranes—Measuring and Modeling
Energies 2020, 13(8), 1946; https://doi.org/10.3390/en13081946 - 15 Apr 2020
Cited by 3
Abstract
Ion exchange membranes are used in different fields of energy and separation technology such as electrodialysis, reverse electrodialysis, and fuel cells. Important aspects are permselectivity, resistance, and water transport. In this paper, we focus on the effect of the bulk NaCl concentration on [...] Read more.
Ion exchange membranes are used in different fields of energy and separation technology such as electrodialysis, reverse electrodialysis, and fuel cells. Important aspects are permselectivity, resistance, and water transport. In this paper, we focus on the effect of the bulk NaCl concentration on the membrane resistance. Data from 36 publications containing 145 datasets using 6 different methods for measuring membrane resistance were compared. This study showed that the membrane resistance is dependent on the method of measuring. Two probable causes are identified: the application of reference electrodes and the presence of direct electrode–membrane contact. In addition, three physical and three phenomenological membrane models were tested by fitting these to the datasets. First, fits in the resistance domain were compared with fits in the conductivity domain. Resistance fits are sensitive to fluctuations in low concentrations, whereas fits in the conductivity domain are subject to nonlinear responses at high concentration. Resistance fits resulted in higher coefficients of determination (R2). Then, the six models were compared. The 1-thread model with two fit parameters was in almost all cases a good start. More improvements were difficult to test due to the restricted number of data points in most of the used publications, although this study shows that the so-called Gierke model (with 4 parameters) fits better than the 3-thread model. Phenomenological models were also tested, but they did not lead to much better fits. Full article
(This article belongs to the Special Issue Blue Energy)
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Open AccessArticle
Turbine Characteristics of Wave Energy Conversion Device for Extraction Power Using Breaking Waves
Energies 2020, 13(4), 966; https://doi.org/10.3390/en13040966 - 21 Feb 2020
Abstract
A new type of wave energy converter which harnesses electricity from onshore breaking waves has been studied at Okinawa Institute of Science and Technology Graduate University (OIST) since 2014. This concept has been demonstrated at a coral beach on the Maldives since 2018. [...] Read more.
A new type of wave energy converter which harnesses electricity from onshore breaking waves has been studied at Okinawa Institute of Science and Technology Graduate University (OIST) since 2014. This concept has been demonstrated at a coral beach on the Maldives since 2018. Wave energy conversion is possible when waves approaching the shore steepen due to decreased water depth resulting in wave breaks near the surface. A steepened wave reaches the critical velocity of 4~6 m/sec shoreward before it breaks. A rotating blade takes advantage of this breaking phenomenon to convert the wave energy into electricity. The work presented here includes an experimental and numerical investigation of a prototype model of the wave energy converter. The turbine having five blades of variable chord lengths, twist angles, and constant thickness profile from hub to tip was simulated under similar flow as well as testing conditions, to predict the turbine performance. A commercial computational fluid dynamic tool SolidWorks Flow Simulation 2018 was used for the simulations at various rotation speeds with a uniform inlet velocity. The modified k-ε with a two-scale wall function turbulence closure model was selected. The validation performed for different test cases showed that the present computational results match in good agreement with the experimental results. Additionally, details performance of the turbine running, and generator characteristics have been reported in this paper. Full article
(This article belongs to the Special Issue Blue Energy)
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Open AccessArticle
Fluid–Structure Interaction and Flow Redistribution in Membrane-Bounded Channels
Energies 2019, 12(22), 4259; https://doi.org/10.3390/en12224259 - 08 Nov 2019
Cited by 2
Abstract
The hydrodynamics of electrodialysis and reverse electrodialysis is commonly studied by neglecting membrane deformation caused by transmembrane pressure (TMP). However, large frictional pressure drops and differences in fluid velocity or physical properties in adjacent channels may lead to significant TMP values. In previous [...] Read more.
The hydrodynamics of electrodialysis and reverse electrodialysis is commonly studied by neglecting membrane deformation caused by transmembrane pressure (TMP). However, large frictional pressure drops and differences in fluid velocity or physical properties in adjacent channels may lead to significant TMP values. In previous works, we conducted one-way coupled structural-CFD simulations at the scale of one periodic unit of a profiled membrane/channel assembly and computed its deformation and frictional characteristics as functions of TMP. In this work, a novel fluid–structure interaction model is presented, which predicts, at the channel pair scale, the changes in flow distribution associated with membrane deformations. The continuity and Darcy equations are solved in two adjacent channels by treating them as porous media and using the previous CFD results to express their hydraulic permeability as a function of the local TMP. Results are presented for square stacks of 0.6-m sides in cross and counter flow at superficial velocities of 1 to 10 cm/s. At low velocities, the corresponding low TMP does not significantly affect the flow distribution. As the velocity increases, the larger membrane deformation causes significant fluid redistribution. In the cross flow, the departure of the local superficial velocity from a mean value of 10 cm/s ranges between −27% and +39%. Full article
(This article belongs to the Special Issue Blue Energy)
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Review

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Open AccessReview
Prospects for Anion-Exchange Membranes in Alkali Metal–Air Batteries
Energies 2019, 12(24), 4702; https://doi.org/10.3390/en12244702 - 10 Dec 2019
Cited by 8
Abstract
Rechargeable alkali metal–air batteries have enormous potential in energy storage applications due to their high energy densities, low cost, and environmental friendliness. Membrane separators determine the performance and economic viability of these batteries. Usually, porous membrane separators taken from lithium-based batteries are used. [...] Read more.
Rechargeable alkali metal–air batteries have enormous potential in energy storage applications due to their high energy densities, low cost, and environmental friendliness. Membrane separators determine the performance and economic viability of these batteries. Usually, porous membrane separators taken from lithium-based batteries are used. Moreover, composite and cation-exchange membranes have been tested. However, crossover of unwanted species (such as zincate ions in zinc–air flow batteries) and/or low hydroxide ions conductivity are major issues to be overcome. On the other hand, state-of-art anion-exchange membranes (AEMs) have been applied to meet the current challenges with regard to rechargeable zinc–air batteries, which have received the most attention among alkali metal–air batteries. The recent advances and remaining challenges of AEMs for these batteries are critically discussed in this review. Correlation between the properties of the AEMs and performance and cyclability of the batteries is discussed. Finally, strategies for overcoming the remaining challenges and future outlooks on the topic are briefly provided. We believe this paper will play a significant role in promoting R&D on developing suitable AEMs with potential applications in alkali metal–air flow batteries. Full article
(This article belongs to the Special Issue Blue Energy)
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Open AccessReview
Modeling and Simulation Studies Analyzing the Pressure-Retarded Osmosis (PRO) and PRO-Hybridized Processes
Energies 2019, 12(2), 243; https://doi.org/10.3390/en12020243 - 14 Jan 2019
Cited by 5
Abstract
Pressure-retarded osmosis (PRO) is viewed as a highly promising renewable energy process that generates energy without carbon emissions in the age of the climate change regime. While many experimental studies have contributed to the quest for an efficiency that would make the PRO [...] Read more.
Pressure-retarded osmosis (PRO) is viewed as a highly promising renewable energy process that generates energy without carbon emissions in the age of the climate change regime. While many experimental studies have contributed to the quest for an efficiency that would make the PRO process commercially viable, computational modeling and simulation studies have played crucial roles in investigating the efficiency of PRO, particularly the concept of hybridizing the PRO process with reverse osmosis (RO). It is crucial for researchers to understand the implications of the simulation and modeling works in order to promote the further development of PRO. To that end, the authors collected many relevant papers and reorganized their important methodologies and results. This review, first of all, presents the mathematical derivation of the fundamental modeling theories regarding PRO including water flux and concentration polarization equations. After that, those theories and thermodynamic theories are then applied to depict the limitations of a stand-alone PRO process and the effectiveness of an RO-PRO hybridized process. Lastly, the review diagnoses the challenges facing PRO-basis processes which are insufficiently resolved by conventional engineering approaches and, in response, presents alternative modeling and simulation approaches as well as novel technologies. Full article
(This article belongs to the Special Issue Blue Energy)
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