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To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD) is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. In particular, the effects of mesh size and structure, time step and rotational velocity have been taken into account for simulation of different wind turbine geometries. The applicative goal of this study is the comparison of the performance between a straight blade vertical axis wind turbine and a helical blade one. Analyses are carried out through the use of computational fluid dynamic ANSYS R Fluent R software, solving the Reynolds averaged Navier-Stokes (RANS) equations. At first, two-dimensional simulations are used in a preliminary setup of the numerical procedure and to compute approximated performance parameters, namely the torque, power, lift and drag coefficients. Then, three-dimensional simulations are carried out with the aim of an accurate determination of the differences in the complex aerodynamic flow associated with the straight and the helical blade turbines. Static and dynamic results are then reported for different values of rotational speed.

Hydrothermal carbonization (HTC) represents an efficient and valuable pre-treatment technology to convert waste biomass into highly dense carbonaceous materials that could be used in a wide range of applications between energy, environment, soil improvement and nutrients recovery fields. HTC converts residual organic materials into a solid high energy dense material (hydrochar) and a liquid residue where the most volatile and oxygenated compounds (mainly furans and organic acids) concentrate during reaction. Pristine hydrochar is mainly used for direct combustion, to generate heat or electricity, but highly porous carbonaceous media for energy storage or for adsorption of pollutants applications can be also obtained through a further activation stage. HTC process can be used to enhance recovery of nutrients as nitrogen and phosphorous in particular and can be used as soil conditioner, to favor plant growth and mitigate desertification of soils. The present review proposes an outlook of the several possible applications of hydrochar produced from any sort of waste biomass sources. For each of the applications proposed, the main operative parameters that mostly affect the hydrochar properties and characteristics are highlighted, in order to match the needs for the specific application.

Hydrothermal carbonization of pure cellulose and birchwood samples was carried out at temperatures between 160 and 280 °C, 0.5 h residence time and biomass-to-water ratio of 20 wt% dry basis, to investigate HTC reactivity of cellulose naturally occurring lignocellulosic biomass. Pure cellulose samples remained unaltered at temperatures up to 220 °C, but significantly decomposed at 230 °C producing a thermal recalcitrant aromatic, high energy-dense material, showing lignin-like behavior. Fourier Transform Infrared spectroscopy (FTIR) showed dehydration and aromatization reactions occurring at temperatures equal or higher than 230 °C for pure cellulose samples while similar increase in aromatization for birchwood hydrochars was evident only at temperatures equal or higher than 260 °C. Acid hydrolysis, Thermogravimetric analysis (TGA) and FTIR suggest that a higher thermal resistance of natural occurring cellulose in birchwood (when compared to pure cellulose sample) could be related to a 'protecting shield' offered by interlinked lignin in the plant matrix.

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