Papers on thermal water desalination by Eliodoro Chiavazzo
Nature communications, 2022
Check for updates Recent studies in passive solar-driven evaporative technologies have introduced... more Check for updates Recent studies in passive solar-driven evaporative technologies have introduced a plethora of new materials and devices which promise higher economic and environmental sustainability in water treatment. However, many challenges remain for the effective adoption of such technologies. Here, we identify three main pillars and the corresponding issues which future research activities should focus on to bring the proposed solutions to the next maturity level. Specifically, our analysis focuses on standards for comparing productivity, strategies to overcome the single stage limit, scalability and robustness.
Nature Sustainability
Although seawater is abundant, desalination is energy-intensive and expensive. Using the sun as a... more Although seawater is abundant, desalination is energy-intensive and expensive. Using the sun as an energy source is attractive for desalinating seawater; however, the performance of state-ofthe-art passive devices is unsatisfactory when operated at less than one sun (<1 kW m-2). Here, we present a completely passive, modular, and low-cost solar thermal distiller for seawater desalination. Each distillation stage is made of two opposed hydrophilic layers separated by a hydrophobic microporous membrane, and it does not require further mechanical ancillaries. Under realistic laboratory and outdoor conditions, we obtained a distillate flow rate of almost 3 L m-2 h-1 from seawater at less than one sun-twice the yield of recent passive device reported in the literature. In perspective, theoretical modelling suggests that the distiller has the potential to further doubling the peak flow rate observed in the current experiments. This layout can satisfy freshwater needs in isolated and impoverished communities, as well as realize self-sufficient floating installations or provide freshwater in emergency conditions.
Nature sustainability, 2017
Although seawater is abundant, desalination is energy intensive and expensive. Using the Sun as a... more Although seawater is abundant, desalination is energy intensive and expensive. Using the Sun as an energy source is attractive for desalinating seawater. Although interesting, current passive devices with no moving parts have unsatisfactory performance when operated with an energy flux lower than 1 kW m−2 (one sun). We present a passive multi-stage and low-cost solar distiller, where efficient energy management leads to significant enhancement in freshwater yield. Each unit stage for complete distillation is made of two hydrophilic layers separated by a hydrophobic microporous membrane, with no other mechanical ancillaries. Under realistic conditions, we demonstrate a distillate flow rate of almost 3 l m−2 h−1 from seawater at less than one sun—twice the yield of recent passive complete distillation systems. Theoretical models also suggest that the concept has the potential to further double the observed distillate rate. In perspective, this system may help satisfy the freshwater needs in isolated and impoverished communities in a sustainable way.
Sustainable freshwater production using passive membrane distillation and waste heat recovery from portable generator sets
Applied Energy
Energy & Environmental Science
The Marangoni effect (associated to salt concentration gradient) is found having an important rol... more The Marangoni effect (associated to salt concentration gradient) is found having an important role to enhance the salt rejection process in passive desalination technologies.
Papers on energy conversion processes and devices by Eliodoro Chiavazzo
Discover nano, 2023
We focus on a novel concept of photosynthetic soft membranes, possibly able to allow the conversi... more We focus on a novel concept of photosynthetic soft membranes, possibly able to allow the conversion of solar energy and carbon dioxide (CO 2) into green fuels. The considered membranes rely on self-assembled functional molecules in the form of soap films. We elaborate a multi-scale and multi-physics model to describe the relevant phenomena, investigating the expected performance of a single soft photosynthetic membrane. First, we present a macroscale continuum model, which accounts for the transport of gaseous and ionic species within the soap film, the chemical equilibria and the two involved photocatalytic half reactions of the CO 2 reduction and water oxidation at the two gas-surfactant-water interfaces of the soap film. Second, we introduce a mesoscale discrete Monte Carlo model, to deepen the investigation of the structure of the functional monolayers. Finally, the morphological information obtained at the mesoscale is integrated into the continuum model in a multi-scale framework. The developed tools are then used to perform sensitivity studies in a wide range of possible experimental conditions, to provide scenarios on fuel production by such a novel approach.
Science Advances, 2020
Space cooling in buildings is anticipated to rise because of an increasing thermal comfort demand... more Space cooling in buildings is anticipated to rise because of an increasing thermal comfort demand worldwide, and this calls for cost-effective and sustainable cooling technologies. We present a proof-of-concept multistage device, where a net cooling capacity and a temperature difference are demonstrated as long as two water solutions at disparate salinity are maintained. Each stage is made of two hydrophilic layers separated by a hydrophobic membrane. An imbalance in water activity in the two layers naturally causes a non-isothermal vapor flux across the membrane without requiring any mechanical ancillaries. One prototype of the device developed a specific cooling capacity of up to 170 W m−2 at a vanishing temperature difference, considering a 3.1 mol/kg calcium chloride solution. To provide perspective, if successfully up-scaled, this concept may help satisfy at least partially the cooling needs in hot, humid regions with naturally available salinity gradients.
Journal of Energy Storage, 2020
Thermal energy storage (TES) allows to extensively exploit solar thermal technologies by effectiv... more Thermal energy storage (TES) allows to extensively exploit solar thermal technologies by effectively handling the mismatch between energy production and demand thus possibly causing a downsizing of generation units. Among thermal energy storage technologies, those based on phase change materials (PCM) are particularly interesting because relatively large latent heat values may guarantee more compact systems (as compared to sensible TES). In this work, we report a numerical and experimental investigation on a hybrid latent-sensible heat storage characterized by a commercial hot water tank integrated with macro-encapsulated phase change materials. Those hybrid systems are interesting as they can possibly increase the overall thermal capacity of a sensible water tank. Despite all this, we demonstrate that increasing the effective storage capacity is a non trivial task with standard conditions and materials. To this end, three different numerical models have been developed and experimentally validated. The first model is based on the enthalpy porosity method and simulates the charge and discharge of a PCM storage unit in a climatic chamber. The second model is a one-dimensional description of the water storage tank without PCM. Finally, the third model is obtained by coupling the previous two and simulates the whole PCM-water thermal storage. This final model was validated through an experimental test, which consisted in inserting 94 modules of PCM in the water tank and observing the resulting thermal behaviour for three days, applying the load curve of a detached house of 200m2. The model proved to be very accurate, with determination coefficients between 92.10% and 99.80% for the considered physical quantities (temperatures and thermal powers). As a main contribution of this work, we proved that the hybrid thermal storage system did not exploit the full latent heat potential of the PCM, since only 40% of it actually changes its phase, due to is thermal transport properties that negatively affect heat transfer.
Computers & Mathematics with Applications, 2014
This work represents a step towards reliable algorithms for reconstructing micro-morphology of el... more This work represents a step towards reliable algorithms for reconstructing micro-morphology of electrode materials of high-temperature protonexchange membrane fuel cells and for performing pore-scale simulations of fluid flow (including rarefaction effects). In particular, we developed a deterministic model for a woven gas diffusion layer (GDL) and a stochastic model for the catalyst layer (CL) based on clusterization of carbon particles.
This work represents a step towards reliable algorithms for reconstructing micro-morphology of el... more This work represents a step towards reliable algorithms for reconstructing micro-morphology of electrode materials of high-temperature proton-exchange membrane fuel cells and for performing pore-scale simulations of fluid flow (including rarefaction effects). In particular, we developed a de-terministic model for a woven gas diffusion layer (GDL) and a stochastic model for the catalyst layer (CL) based on clusterization of carbon particles. We verified that both developed models accurately recover the experimental values of permeability, without any special ad-hoc tuning. Moreover, we investigated the effect of catalyst particle distributions inside the CL on the degree of clusterization and on the microscopic fluid flow, which is relevant for degradation modelling (e.g. loss of phosphoric acid). The three-dimensional pore-scale simulations of fluid flow for the direct numerical calculation of
This work represents a step towards reliable algorithms for reconstructing micro-morphology of el... more This work represents a step towards reliable algorithms for reconstructing micro-morphology of electrode materials of high-temperature protonexchange membrane fuel cells and for performing pore-scale simulations of fluid flow (including rarefaction effects). In particular, we developed a deterministic model for a woven gas diffusion layer (GDL) and a stochastic model for the catalyst layer (CL) based on clusterization of carbon particles.
Gas-dynamic and electro-chemical optimization of catalyst layers in high temperature polymeric electrolyte membrane fuel cells
International Journal of Hydrogen Energy, 2015
ABSTRACT We investigate the impact of catalyst (Pt) particle distribution on gas dynamics, electr... more ABSTRACT We investigate the impact of catalyst (Pt) particle distribution on gas dynamics, electro-chemistry and consequently the performance of high temperature polymeric electrolyte membrane (HTPEM) fuel cells. We demonstrate that optimal distribution of catalyst can be used as an effective mitigation strategy for phosphoric acid loss and crossover of reagents through the membrane. First, we recognize that one of the reasons for performance degradation of HTPEM fuel cells originates from the gas dynamic action at the interface between the catalyst layer and membrane. Hence, we show that this can be greatly alleviated by choosing a proper catalyst particle distribution within the catalyst layer (CL). A simplified three-dimensional macroscopic model of the membrane electrode assembly (MEA) with catalyst layer made of three or five sublayers with different catalyst loadings, have been developed to analyze the effect of the proposed mitigation strategy on gas dynamics within the catalyst layer and the overall cell performance. This simplified macroscopic model predicts significant stress reduction (up to 4 times) using a feasible mitigation strategy, at the cost of only 9% efficiency reduction at high current densities.
Applied Sciences
Water pasteurization has the potential to overcome some of the drawbacks of more conventional dis... more Water pasteurization has the potential to overcome some of the drawbacks of more conventional disinfection techniques such as chlorination, ozonation and ultraviolet radiation treatment. However, the high throughput of community water systems requires energy-intensive processes, and renewable energy sources have the potential to improve the sustainability of water pasteurization plants. In case of water pasteurization by solar thermal treatment, the continuity of operation is limited by the intermittent availability of the solar irradiance. Here we show that this problem can be addressed by a proper design of the plant layout, which includes a thermal energy storage system and an auxiliary gas boiler. Based on a target pasteurization protocol validated by experiments, a complete lumped-component model of the plant is developed and used to determine the operating parameters and size of the components for a given delivery flow rate. Finally, we report an economic analysis of the propo...
Direct solar absorption has been considered often in the past as a possible configuration of sola... more Direct solar absorption has been considered often in the past as a possible configuration of solar thermal collectors for residential and small commercial applications. Of course, a direct absorption could improve the performance of solar collectors by skipping one step of the heat transfer mechanism of standard devices and by modifying the temperature distribution inside the collector. In fact, classical solar thermal collectors have a metal sheet as absorber, designed such that water has the minimum temperature in each transversal section, in order to collect as much as possible the solar thermal energy. On the other hand, in a direct configuration, the hottest part of the system is the operating fluid and this allows to have a more efficient conversion. Nanofluids, i.e. fluids with a suspension of nano-particles, as carbon nano-horns, could be a good and innovative family of absorbing fluids, for their higher absorption coefficient with respect to the base fluid and stability under moderate temperature gradients. Moreover, carbon nanohorns offer the significant advantage to be non-toxic unlike other carbon nanoparticles (e.g. carbon nanotubes). In this work, an original 3D model of the absorption phenomena in nano-fluids flowing in a cylindrical tube is coupled with a CFD analysis of the flow and temperature field. Recent measurements of the optical properties of nano-fluids with different concentrations have been used for the radiation heat transfer modeling and included in the fluid dynamic modeling as well. Heat losses due to conduction, convection and radiation at the boundaries are included in the model. The results are compared with the typical performance of flat solar collectors present on the market.
Direct solar absorption has been considered often in the past as a possible configuration of sola... more Direct solar absorption has been considered often in the past as a possible configuration of solar thermal collectors for residential and small commercial applications. Of course, a direct absorption could improve the performance of solar collectors by skipping one step of the heat transfer mechanism of standard devices and by modifying the temperature distribution inside the collector. In fact, classical solar thermal collectors have a metal sheet as absorber, designed such that water has the minimum temperature in each transversal section, in order to collect as much as possible the solar thermal energy. On the other hand, in a direct configuration, the hottest part of the system is the operating fluid and this allows to have a more efficient conversion. Nanofluids, i.e. fluids with a suspension of nano-particles, as carbon nano-horns, could be a good and innovative family of absorbing fluids, for their higher absorption coefficient with respect to the base fluid and stability under moderate temperature gradients. Moreover, carbon nanohorns offer the significant advantage to be non-toxic unlike other carbon nanoparticles (e.g. carbon nanotubes). In this work, an original 3D model of the absorption phenomena in nano-fluids flowing in a cylindrical tube is coupled with a CFD analysis of the flow and temperature field. Recent measurements of the optical properties of nano-fluids with different concentrations have been used for the radiation heat transfer modeling and included in the fluid dynamic modeling as well. Heat losses due to conduction, convection and radiation at the boundaries are included in the model. The results are compared with the typical performance of flat solar collectors present on the market.
Papers on energy materials and fluids by Eliodoro Chiavazzo
Materials Today, 2023
In recent years, an increasing number of diverse Engineered Nano-Materials (ENMs), such as nanopa... more In recent years, an increasing number of diverse Engineered Nano-Materials (ENMs), such as nanoparticles and nanotubes, have been included in many technological applications and consumer products. The desirable and unique properties of ENMs are accompanied by potential hazards whose impacts are difficult to predict either qualitatively or in a quantitative and predictive manner.
Alongside established methods for experimental and computational characterisation, physics-based modelling tools like molecular dynamics are increasingly considered in Safe and Sustainability-by-design (SSbD) strategies that put user health and environmental impact at the centre of the design and development of new products. Hence, the further development of such tools can support safe and sustainable innovation and its regulation.
This paper stems from a community effort and presents the outcome of a four-year-long discussion on the benefits, capabilities and limitations of adopting physics-based modelling for computing suitable features of nanomaterials that can be used for toxicity assessment of nanomaterials in combination with data-based models and experimental assessment of toxicity endpoints. We review modern multiscale physics-based models that generate advanced system-dependent (intrinsic) or time and environment-dependent (extrinsic) descriptors/features of ENMs (primarily, but not limited to nanoparticles, NPs), with the former being related to the bare NPs and the latter to their dynamic fingerprinting upon entering biological media. The focus is on (i) effectively representing all nanoparticle attributes for multicomponent nanomaterials, (ii) generation and inclusion of intrinsic nanoform properties, (iii) inclusion of selected extrinsic properties, (iv) the necessity of considering distributions of structural advanced features rather than only averages. This review enables us to identify and highlight a number of key challenges associated with ENMs’ data generation, curation, representation and use within machine learning or other advanced data-driven models to ultimately enhance toxicity assessment. Finally, the set up of dedicated databases as well as the development of grouping and read-across strategies based on the mode of action of ENMs using omics methods are identified as emerging methodologies for safety assessment and reduction of animal testing.
Journal of Energy Storage, 2022
In this review we aim at providing an up-to-date and comprehensive overview on the use of additiv... more In this review we aim at providing an up-to-date and comprehensive overview on the use of additives within selected Phase Change Materials (PCMs) from both an experimental and more theoretical perspective. Traditionally, mostly focusing on short-term thermal energy storage applications, the addition of (nano)fillers has been extensively studied to enhance unsatisfactory thermo-physical properties in PCMs, in order to overcome limiting aspects such as low thermal conductivity possibly leading to unacceptable long charging and/or discharging periods and inefficient heat-storage systems. On the other hand, here we focus on the most important PCMs for long-term thermal energy storage (i.e. spanning from classical solid-to-liquid to more recent solid-to-solid PCMs) and make an effort in shedding light on the role played not only by additives but also (and importantly) by additivation protocols on the resulting thermo-physical and stability properties. While introducing and connecting to general advantages related to additivation in classical PCMs for thermal energy storage, we discuss specifically the use of additives in sugar alcohols and sodium acetate trihydrate, as well as in novel emerging classes of PCMs capable of undergoing solid-to-solid transitions and showing promising features for long-term heat storage materials. We highlight outstanding issues in the use of additives for property enhancement in PCMs and expect that the present work can contribute to expand the current understanding and field of application of the less mature PCMs for thermal energy storage, especially as far as long term applications are concerned.
npj Computational Materials
We focus on gas sorption within metal-organic frameworks (MOFs) for energy applications and ident... more We focus on gas sorption within metal-organic frameworks (MOFs) for energy applications and identify the minimal set of crystallographic descriptors underpinning the most important properties of MOFs for CO2 and H2O. A comprehensive comparison of several sequential learning algorithms for MOFs properties optimization is performed and the role played by those descriptors is clarified. In energy transformations, thermodynamic limits of important figures of merit crucially depend on equilibrium properties in a wide range of sorbate coverage values, which is often only partially accessible, hence possibly preventing the computation of desired objective functions. We propose a fast procedure for optimizing specific energy in a closed sorption energy storage system with only access to a single water Henry coefficient value and to the specific surface area. We are thus able to identify hypothetical candidate MOFs that are predicted to outperform state-of-the-art water-sorbent pairs for the...
NPJ computational materials, 2021
Several studies have been recently reported in the literature on sorption properties of MOFs with... more Several studies have been recently reported in the literature on sorption properties of MOFs with a number of organic sorbates, such as ethanol and methanol. Surprisingly, still few studies have been reported on water sorbate despite its large availability, low cost and environmental sustainability, and the screening of a large number of hypothetical MOFs-water working pairs for engineering applications is still challenging. Based on a recently reported database of over 5000 hypothetical MOFs, a first contribution of this study is the identification of the minimal set of crystallographic descriptors underpinning the most important sorption properties of MOFs for CO2 and, importantly, for H2O. Furthermore, a comprehensive comparison of several Sequential Learning (SL) algorithms for MOFs properties optimization is carried out and the role played by the above minimal set of crystallographic descriptors clarified. In sorption-based energy transformations, thermodynamic limits of import...
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Papers on thermal water desalination by Eliodoro Chiavazzo
Papers on energy conversion processes and devices by Eliodoro Chiavazzo
Papers on energy materials and fluids by Eliodoro Chiavazzo
Alongside established methods for experimental and computational characterisation, physics-based modelling tools like molecular dynamics are increasingly considered in Safe and Sustainability-by-design (SSbD) strategies that put user health and environmental impact at the centre of the design and development of new products. Hence, the further development of such tools can support safe and sustainable innovation and its regulation.
This paper stems from a community effort and presents the outcome of a four-year-long discussion on the benefits, capabilities and limitations of adopting physics-based modelling for computing suitable features of nanomaterials that can be used for toxicity assessment of nanomaterials in combination with data-based models and experimental assessment of toxicity endpoints. We review modern multiscale physics-based models that generate advanced system-dependent (intrinsic) or time and environment-dependent (extrinsic) descriptors/features of ENMs (primarily, but not limited to nanoparticles, NPs), with the former being related to the bare NPs and the latter to their dynamic fingerprinting upon entering biological media. The focus is on (i) effectively representing all nanoparticle attributes for multicomponent nanomaterials, (ii) generation and inclusion of intrinsic nanoform properties, (iii) inclusion of selected extrinsic properties, (iv) the necessity of considering distributions of structural advanced features rather than only averages. This review enables us to identify and highlight a number of key challenges associated with ENMs’ data generation, curation, representation and use within machine learning or other advanced data-driven models to ultimately enhance toxicity assessment. Finally, the set up of dedicated databases as well as the development of grouping and read-across strategies based on the mode of action of ENMs using omics methods are identified as emerging methodologies for safety assessment and reduction of animal testing.
Alongside established methods for experimental and computational characterisation, physics-based modelling tools like molecular dynamics are increasingly considered in Safe and Sustainability-by-design (SSbD) strategies that put user health and environmental impact at the centre of the design and development of new products. Hence, the further development of such tools can support safe and sustainable innovation and its regulation.
This paper stems from a community effort and presents the outcome of a four-year-long discussion on the benefits, capabilities and limitations of adopting physics-based modelling for computing suitable features of nanomaterials that can be used for toxicity assessment of nanomaterials in combination with data-based models and experimental assessment of toxicity endpoints. We review modern multiscale physics-based models that generate advanced system-dependent (intrinsic) or time and environment-dependent (extrinsic) descriptors/features of ENMs (primarily, but not limited to nanoparticles, NPs), with the former being related to the bare NPs and the latter to their dynamic fingerprinting upon entering biological media. The focus is on (i) effectively representing all nanoparticle attributes for multicomponent nanomaterials, (ii) generation and inclusion of intrinsic nanoform properties, (iii) inclusion of selected extrinsic properties, (iv) the necessity of considering distributions of structural advanced features rather than only averages. This review enables us to identify and highlight a number of key challenges associated with ENMs’ data generation, curation, representation and use within machine learning or other advanced data-driven models to ultimately enhance toxicity assessment. Finally, the set up of dedicated databases as well as the development of grouping and read-across strategies based on the mode of action of ENMs using omics methods are identified as emerging methodologies for safety assessment and reduction of animal testing.
designed and tested. This sensor exploits the notion of thermal guard and is purposely designed to deal
with metal samples made by additive manufacturing, such as direct metal laser sintering (DMLS). For val-
idation purposes, we utilize both experimental literature data and a computational fluid dynamic (CFD)
model: Maximum and average deviations from CDF model in terms of the Nusselt number are on the
order of 13:7% and 6:3%, respectively while deviations from literature data are even smaller. Similar
works in the literature often have the necessity of maintaining one-directional heat flows along the main
dimension of a conducting bar using insulating materials. Such an approach can be critical for small
fluxes due to the curse of heat conduction losses along secondary directions. As a result, it is necessary
to estimate those secondary fluxes (e.g. by numerical models), thus making the measurement difficult
and indirect. On the other hand, depending on the manufacturing accuracy, the present sensor enables
to practically reduce at will those losses, with direct measurement of the heat flux. To our knowledge,
the adoption of thermal guard is not a common practice in convective heat transfer, especially when local
measurements are of interest. We hope that this study may (i) shed light on the usefulness of the
approach in this field; and (ii) provide an effective tool for future investigation on electronic cooling
and convective heat transfer enhancement by micro-/nano-structured surfaces. Owing to a number of
features of the proposed device, we suggest that it can be prospectively utilized in the near future (i)
for industrial applications (due to simplicity and robustness of the design); (ii) for high temperature mea-
surements (unlike foil sensors, no delamination issues can be experienced); (iii) in the context of micro-
electromechanical systems (MEMS) (easy to miniaturize).
Nanofluids are suspensions of nanoparticles and fibers which have recently attracted much attention because of their superior thermal properties. Nevertheless, it was proven that, due to modest dispersion of nanoparticles, such high expectations often remain unmet. In this article, by introducing the notion of nanofin, a possible solution is envisioned, where nanostructures with high aspect-ratio are sparsely attached to a solid surface (to avoid a significant disturbance on the fluid dynamic structures), and act as efficient thermal bridges within the boundary layer. As a result, particles are only needed in a small region of the fluid, while dispersion can be controlled in advance through design and manufacturing processes.
Results
Toward the end of implementing the above idea, we focus on single carbon nanotubes to enhance heat transfer between a surface and a fluid in contact with it. First, we investigate the thermal conductivity of the latter nanostructures by means of classical non-equilibrium molecular dynamics simulations. Next, thermal conductance at the interface between a single wall carbon nanotube (nanofin) and water molecules is assessed by means of both steady-state and transient numerical experiments.
Conclusions
Numerical evidences suggest a pretty favorable thermal boundary conductance (order of 107 W·m-2·K-1) which makes carbon nanotubes potential candidates for constructing nanofinned surfaces.
Nanofluids are suspensions of nanoparticles and fibers which have recently attracted much attention because of their superior thermal properties. Nevertheless, it was proven that, due to modest dispersion of nanoparticles, such high expectations often remain unmet. In this article, by introducing the notion of nanofin, a possible solution is envisioned, where nanostructures with high aspect-ratio are sparsely attached to a solid surface (to avoid a significant disturbance on the fluid dynamic structures), and act as efficient thermal bridges within the boundary layer. As a result, particles are only needed in a small region of the fluid, while dispersion can be controlled in advance through design and manufacturing processes.
Results
Toward the end of implementing the above idea, we focus on single carbon nanotubes to enhance heat transfer between a surface and a fluid in contact with it. First, we investigate the thermal conductivity of the latter nanostructures by means of classical non-equilibrium molecular dynamics simulations. Next, thermal conductance at the interface between a single wall carbon nanotube (nanofin) and water molecules is assessed by means of both steady-state and transient numerical experiments.
Conclusions
Numerical evidences suggest a pretty favorable thermal boundary conductance (order of 107 W·m-2·K-1) which makes carbon nanotubes potential candidates for constructing nanofinned surfaces.