Inadequate water supply, sanitation and hygiene in remote locations, developing countries, and disaster zones fuel the growing demand for efficient small-scale desalination technologies. The aim is to provide high-quality freshwater to water-stressed and disaster-stricken communities even in the absence of energy infrastructure. The major key drivers behind the development of these technologies are the low cost of materials, the flexibility of the technology, the sustainability of the freshwater production, and the long-term stability of the device performance. However, the main challenge is to achieve stable performance by either preventing or mitigating salt accumulation during the desalination process. We present a multistage passive solar distiller whose key-strength is an optimized geometry leading to enhanced water yield (as compared to similar state of the art technologies) and spontaneous salt rejection. A comprehensive theoretical study is conducted to explain the apparently paradoxical experimental effective transport exceeding classical diffusion by two orders of magnitude. In our study, the Marangoni effect is included at the water–air interface and it stems from spatial gradients of surface tension. Interestingly, theoretical and experimental results demonstrate that the device is able to reject overnight all the salt accumulated on each evaporator during daytime operation. Furthermore, under realistic conditions, a distillate flow rate of almost 2 L m⁻² h⁻¹ from seawater at less than one sun illumination has been experimentally observed. The reported mechanism of the enhanced salt rejection process may have tremendous implications in the desalination field as it paves the way to the design of a new generation of hydrophilic and porous materials for passive thermal desalination. We envision that such a technology can help provide cheap drinking water, in a robust way, during emergency conditions, while maintaining stable performance over a long time.

The transport of water in nanoconfined geometries is different from bulk phase and has tremendous implications in nanotechnology and biotechnology. Here molecular dynamics is used to compute the self-diffusion coefficient D of water within nanopores, around nanoparticles, carbon nanotubes and proteins. For almost 60 different cases, D is found to scale linearly with the sole parameter θ as D(θ)=D_B[1+(D_C/D_B−1)θ], with D_B and D_C the bulk and totally confined diffusion of water, respectively. The parameter θ is primarily influenced by geometry and represents the ratio between the confined and total water volumes. The D(θ) relationship is interpreted within the thermodynamics of supercooled water. As an example, such relationship is shown to accurately predict the relaxometric response of contrast agents for magnetic resonance imaging. The D(θ) relationship can help in interpreting the transport of water molecules under nanoconfined conditions and tailoring nanostructures with precise modulation of water mobility.

Engineered suspensions of nanosized particles (nanofluids) are characterized by superior thermal properties. Due to the increasing need for ultrahigh performance cooling in many industries, nanofluids have been widely investigated as next-generation coolants. However, the multiscale nature of nanofluids implies nontrivial relations between their design characteristics and the resulting thermo-physical properties, which are far from being fully understood. This pronounced sensitivity is the main reason for some contradictory results among both experimental evidence and theoretical considerations presented in the literature. In this Review, the role of fundamental heat and mass transfer mechanisms governing thermo-physical properties of nanofluids is assessed, from both experimental and theoretical point of view. Starting from the characteristic nanoscale transport phenomena occurring at the particle-fluid interface, a comprehensive review of the influence of geometrical (particle shape, size and volume concentration), physical (temperature) and chemical (particle material, pH and surfactant concentration in the base fluid) parameters on the nanofluid properties was carried out. Particular focus was devoted to highlight the advantages of using nanofluids as coolants for automotive heat exchangers, and a number of design guidelines was suggested for balancing thermal conductivity and viscosity enhancement in nanofluids. This Review may contribute to a more rational design of the thermo-physical properties of particle suspensions, therefore easing the translation of nanofluid technology from small-scale research laboratories to large-scale industrial application

A comprehensive understanding of molecular transport within nanoporous materials remains elusive in a broad variety of engineering and biomedical applications. Here, experiments and atomistic simulations are synergically used to elucidate the non-trivial interplay between nanopore hydrophilicity and surface barriers on the overall water transport through zeolite crystals. At these nanometre-length scales, these results highlight the dominating effect of surface imperfections with reduced permeability on the overall water transport. A simple diffusion resistance model is shown to be sufficient to capture the effects of both intracrystalline and surface diffusion resistances, thus properly linking simulation to experimental evidence. This work suggests that future experimental work should focus on eliminating/overcoming these surface imperfections, which promise an order of magnitude improvement in permeability.