Critical aspects to enable viable solar-driven evaporative technologies for water treatment

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

Looking for massive carbon capture

Afforestation on drylands can help mitigate climate change through carbon sequestration, but the water and energy implications can hinder implementation. A study now investigates the environmental and economic potential of afforestation enabled by desalination plants powered by renewable electricity

Fast computation of multi-scale combustion systems

In the present work, we illustrate the process of constructing a simplified model for complex multi-scale combustion systems. To this end, reduced models of homogeneous ideal gas mixtures of methane and air are first obtained by the novel Relaxation Redistribution Method (RRM) and thereafter used for the extraction of all the missing variables in a reactive flow simulation with a global reaction mode

Realizing Symmetry-Breaking Architectures in Soap Films

We show here that soap films—typically expected to host symmetric molecular arrangements—can be constructed with differing opposite surfaces, breaking their symmetry, and making them reminiscent of functional biological motifs found in nature. Using fluorescent molecular probes as dopants on different sides of the film, resonance energy transfer could be employed to confirm the lack of symmetry, which was found to persist on timescales of several minutes. Further, a theoretical analysis of the main transport phenomena involved yielded good agreement with the experimental observations

The notion of energy through multiple scales: From a molecular level to fluid flows and beyond

In the present paper, we review the consistent definition of macroscopic total energy in classical fluid mechanics, as a function of the microscopic canonical Hamiltonian field, based on a Lennard-Jones model with some spatially varying external field. The macroscopic total energy (sum of mechanical and internal energy) is proved to be equal to the equilibrium ensemble-averaged Hamiltonian. In particular, the conditions for including the effects of the external field both in the macroscopic potential energy and in the internal energy are discussed. {We present the notion of energy as defined in different scientific communities, starting from the standard macroscopic systems all the way down to small ones, which are gaining an increasing popularity

Overview of the entropy production of incompressible and compressible fluid dynamics

In this paper, we present an overview of the entropy production in fluid dynamics in a systematic way. First of all, we clarify a rigorous derivation of the incompressible limit for the Navier–Stokes–Fourier system of equations based on the asymptotic analysis, which is a very well known mathematical technique used to derive macroscopic limits of kinetic equations (Chapman–Enskog expansion and Hilbert expansion are popular methodologies). This allows to overcome the theoretical limits of assuming that the material derivative of the density simply vanishes. Moreover, we show that the fundamental Gibbs relation in classical thermodynamics can be applied to non-equilibrium flows for generalizing the entropy and for expressing the second law of thermodynamics in case of both incompressible and compressible flows. This is consistent with the thermodynamics of irreversible processes and it is an essential condition for the design and optimization of fluid flow devices. Summarizing a theoretical framework valid at different regimes (both incompressible and compressible) sheds light on entropy production in fluid mechanics, with broad implications in applied mechanics

THERMAL BOUNDARY CONDUCTANCE OF CARBON NANOFINS

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. Introducing the notion of nanofin, a possible advancement was envisioned, where nanostructures with high aspect- ratio are sparsely attached to a solid surface and act as thermal bridges within the boundary layer (E. Chiavazzo, P. Asinari, Nanoscale Research Letters, 2011). In this context, we focus on single carbon nanotubes to enhance heat transfer between a surface and a fluid in contact with it. 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. Numerical evidences suggest a pretty favorable thermal boundary conductance (order of 10^7 Wm−2 K−1 ) which makes carbon nanotubes potential candidates for constructing nanofinned surfaces

Simplification of reactive systems by the Relaxation Redistribution Method (RRM)

We review the novel Relaxation Redistribution Method (RRM) for the construction of accurate discrete approximations of slow invariant manifolds. Both formula- tions (global and local) are discussed. A fully adaptive local formulation, with a simple implementation in any dimension, is worked out and illustrated with an example of autoignition of the hydrogen-air mixture