1,720,989 research outputs found
Solar energy technologies for passive and low-cost water desalination
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Passive solar high-yield seawater desalination by modular and low-cost distillation
No full textAlthough 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
A comprehensive formalism for air-gap membrane distillation applied to the design of full-scale modules with direct solar heating
Full text linkAir-gap membrane distillation (AGMD) is used to extract volatile compounds from a heated feed solution,
through a porous hydrophobic membrane, into a cooled compartment, then recovered by condensation. AGMD is
a promising technology for desalination and aqueous concentration, but its scale-up is limited by incomplete
physical descriptions of the module physics. This work proposes a new CFD-based multiphysics framework to
design AGMD full-scale plate-and-frame modules for freshwater extraction. The three physics features comprised
within an AGMD module are first formalized: (i) the flow of a solution in contact with a porous membrane; (ii)
gas mixture (vapor) transport through a porous membrane; (iii) vapor condensation on a (vertical) surface. They
are thus combined into a consistent formalism of the AGMD module physics, with a particular focus on gas
transport built upon the Maxwell-Stefan theory, which is here improved to account for medium vapor saturation.
Model predictions are validated experimentally against lab-scale AGMD data for feed temperature up to 60 ◦C.
The model is then employed to assess full-scale flat-sheet modules, connected in series, and enhanced with direct
solar heating. Simulations reveal that system productivity is highly sensitive to configuration (single vs. multi-
module; bulk solar vs. direct solar heating), with optimal productivity achieved with considerably different
module compartment design and process parameters. When enhanced with direct solar heating, system optimal
productivity can increase by up to 230 % compared to standard configurations. This formalism provides a robust
basis for AGMD modules design and prior to their effective integration into real-world desalination system
Exergy analysis of solar desalination systems based on passive multi-effect membrane distillation
Full text linkImproving the efficiency and sustainability of water treatment technologies is crucial to reduce energy consumption and environmental pollution. Solar-driven devices have the potential to supply off-grid areas with freshwater through a sustainable approach. Passive desalination driven by solar thermal energy has the additional advantage to require only inexpensive materials and easily maintainable components. The bottleneck to the widespread diffusion of such solar passive desalination technologies is their lower productivity with respect to active ones. A completely passive, multi-effect membrane distillation device with an efficient use of solar energy and thus a remarkable enhancement in distillate productivity has been recently proposed. The improved performance of this distillation device comes from the efficient exploitation of low-temperature thermal energy to drive multiple distillation processes. In this work, we analyze the proposed distillation technology by a more in-depth thermodynamic detail, considering a Second Law analysis. We then report a detailed exergy analysis, which allows to get insights on the production of irreversibilities in each component of the assembly. These calculations provide guidelines for the possible optimization of the device, since simple changes in the original configuration may easily yield up to a 46% increase in the Second Law efficiency
Dynamic PCM for high-performance latent thermal energy storage: A numerical and parametric study
No full textThis work presents a theoretical study on dynamic PCM (dynPCM) systems for latent thermal energy storage and high-flux thermal management. First, a 2D numerical model based on the enthalpy-porosity method is validated against established experimental data, accurately predicting the transient melt layer thickness, surface temperature of the heating plate, and melting speed. Results show that dynPCM shortens the charging and discharging times by up to 55% and 30.8%, respectively, compared to classical constrained melting (also termed conventional PCM). Moreover, dynPCM can store up to 35%-37% more energy in latent form under the same heat supply conditions. Building on this validated model, a parametric analysis is conducted using dimensionless groups (Stefan, Peclet, and Reynolds numbers) to examine the effects of thermophysical properties and external operating conditions on system performance at steady state. The study elucidates how latent heat, thermal conductivity, viscosity, and operating pressure collectively govern melt layer thickness, thermal resistance, and pumping power. Finally, an analytical correlation for predicting the heating plate surface temperature is proposed, significantly reducing the need for computationally expensive simulations
Process optimization of osmotic membrane distillation for the extraction of valuable resources from water streams
Full text linkThe rising demand for sustainable wastewater management and high-value resource recovery is pressing industries involved in, e.g., textiles, metals, and food production, to adopt energy-efficient and flexible liquid separation methods. The current techniques often fall short in achieving zero liquid discharge and enhancing socio-economic growth sustainably. Osmotic membrane distillation (OMD) has emerged as a low-temperature separation process designed to concentrate valuable elements and substances in dilute feed streams. The efficacy of OMD hinges on the solvent’s migration from the feed to the draw stream through a hydrophobic membrane, driven by the vapor pressure difference induced by both temperature and concentration gradients. However, the intricate interplay of heat and mass processes steering this mechanism is not yet fully comprehended or accurately modeled. In this research, we conducted a combined theoretical and experimental study to explore the capabilities and thermodynamic limitations of OMD. Under diverse operating conditions, the experimental campaign aimed to corroborate our theoretical assertions. We derived a novel equation to govern water flux based on foundational principles and introduced a streamlined version for more straightforward application. Our findings spotlight complex transport-limiting and self-adjusting mechanisms linked with temperature and concentration polarization phenomena. Compared with traditional methods like membrane distillation and osmotic dilution, which are driven by solely temperature or concentration gradients, OMD may provide improved and flexible performance in target applications. For instance, we show that OMD—if properly optimized—can achieve water vapor fluxes 50% higher than osmotic dilution. Notably, OMD operation at reduced feed temperatures can lead to energy savings ranging between 5 and 95%, owing to the use of highly concentrated draw solutions. This study underscores the potential of OMD in real-world applications, such as concentrating lithium in wastewater streams. By enhancing our fundamental understanding of OMD’s potential and constraints, we aim to broaden its adoption as a pivotal liquid separation tool, with focus on sustainable resource recovery
Rocket Dynamics of Capped Nanotubes: A Molecular Dynamics Study
Full text linkThe study of nanoparticle motion has fundamental relevance in a wide range of nanotechnology-based fields. Molecular dynamics simulations offer a powerful tool to elucidate the dynamics of complex systems and derive theoretical models that facilitate the invention and optimization of novel devices. This research contributes to this ongoing effort by investigating the motion of one-end capped carbon nanotubes within an aqueous environment through extensive molecular dynamics simulations. By exposing the carbon nanotubes to localized heating, propelled motion with velocities reaching up to about 0.08 nm/ps was observed. Through systematic exploration of various parameters such as temperature, nanotube diameter, and size, we were able to elucidate the underlying mechanisms driving propulsion. Our findings demonstrate that the propulsive motion predominantly arises from a rocket-like mechanism facilitated by the progressive evaporation of water molecules entrapped within the carbon nanotube. Therefore, this study focuses on the complex interplay between nanoscale geometry, environmental conditions, and propulsion mechanisms in capped nanotubes, providing relevant insights into the design and optimization of nanoscale propulsion systems with various applications in nanotechnology and beyond
Trending applications of Phase Change Materials in sustainable thermal engineering: An up-to-date review
Full text linkThe on-going search for increasingly sustainable and efficient thermal energy management across a wide range of sectors leads to continuous exploration of innovative solutions. In this context, phase change materials (PCMs) have emerged as key solutions for thermal energy storage and reuse, offering versatility in addressing contemporary energy challenges. Through this review, we offer a comprehensive critical analysis of the latest developments in PCMs-based technology and their emerging applications within energy systems. First, the conducted investigation highlights the most important drivers stimulating the use of PCMs, namely, the miniaturization of electronic devices, the fluctuating nature of renewable energy sources, and the urge to design smart buildings and textiles. Here, we therefore discuss the integration of PCMs into electronic systems characterized by high heat fluxes, lithium-ion batteries, solar energy systems (including photovoltaic, desalination systems), building materials and textiles to offer wearable solutions for enhanced thermal comfort. Outlining around 100 various cases, PCMs emerge as particularly suitable to ensure optimal operating temperature ranges, to extend lifespan of the devices and ultimately to improve overall system energy efficiency. Beyond potential, challenges such as material leakage, long-term durability, and cost-effectiveness are discussed. By focusing on literature post-2022, the proposed review aims to condense the latest numerical and experimental research findings, spotlight emerging trends, and identify challenges to promote broader and long-term adoption of PCM-based systems. By providing a holistic perspective on PCM applications, we emphasize their potential in achieving sustainable and efficient energy management and provide insights to encourage future cross-disciplinary research and innovation
Topology-Optimized Latent Heat Battery: Benchmarking Against a High-Performance Geometry
Full text linkThis study presents a topology optimization approach to enhance the discharging performance of a latent heat thermal energy storage (LHTES) system using paraffin wax as the phase-change material (PCM) and a high-conductivity aluminium structure. Solidification is primarily governed by conduction, and the average heat transfer rate during this process is significantly lower than during melting; therefore, the optimization focused on the discharge phase. In a previous study, a novel LHTES device based on a Cartesian lattice was investigated experimentally and numerically. The validated numerical model from that study was adopted as the reference and used in a 2D topology optimization study based on the Solid Isotropic Material with Penalization (SIMP) method. The objective was to promote more uniform temperature distribution and reduce discharging time while maintaining the same aluminium volume fraction as in the reference device. Topology optimization produced a branched fin design, which was then extruded into a 3D model for comparison with the reference geometry. The optimized design resulted in improved temperature uniformity and a faster solidification process. Specifically, the time required to solidify 90% of the PCM was reduced by 12.3%, while the time to release 90% of the latent heat during the solidification process improved by 7.6%
Installation of a Concentrated Solar Power System for the Thermal Needs of Buildings or Industrial Processes
Full text linkSolar energy is one of the main alternatives to carbon-intensive sources of energy. However, limited attention has been devoted to small-scale (<10 kW) concentrated solar power systems, which are capable to provide high-temperature heat to buildings or industrial processes. In this work, we describe the concentrated solar power system (7.4 kW thermal power) with dual axis solar tracker installed at Politecnico di Torino. The solar concentrator system is coupled to a sensible heat storage by a plate heat exchanger. Here, we provide preliminary data on the system efficiency and compare it to typical values obtained by flat plates or evacuated tubes collectors. The generated high-temperature thermal power is suitable for both domestic hot water, heating and cooling, and industrial purposes
- …
