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Erkey, Can/0000-0001-6539-7748; sahin, ibrahim/0000-0001-9321-9906 ; WOS:000461123600003 ; PubMed: 30674780 ; Supercritical drying of gels is considered as the most important step of aerogel production since it enables preservation of the three-dimensional pore structure which lead to unique material properties such as high porosity, low density, and large surface area. An understanding of the kinetics of supercritical drying is necessary to provide insight into material development, scale-up, and optimization of the aerogel manufacturing process. Thus, investigation of supercritical drying is gaining increased attention in recent years. This review paper covers the experimental considerations and techniques to study the kinetics of supercritical drying, fundamental mass transfer mechanisms during the drying process and modeling efforts to predict the drying kinetics for varying operating conditions and gel properties. Transport phenomena involving diffusion, convection, spillage by volume expansion, and axial dispersion are discussed by providing the fundamental equations and empirical correlations to predict transfer coefficients. A detailed review of literature covering experimental and theoretical studies on kinetics of supercritical drying is presented. ; European Union's Horizon 2020 research and innovation program [685648] ; We gratefully acknowledge European Union's Horizon 2020 research and innovation program (under grant agreement no. 685648) for funding and support.

In this chapter, we consider a randomly-scaled Gaussian process and discuss a number of applications to model fractional diffusion. Actually, this approach can be understood as a Gaussian diffusion in a medium characterized by a population of scales. This interpretation supports the idea that fractional diffusion emerges from standard diffusion occurring in a complex medium. ; BERC 2014-2017 (Basque Government); BCAM Severo Ochoa excellence accreditation SEV-2013-0323 (Spanish Ministry of Economy and Competitiveness MINECO);

Flock growth kinetics was investigated in baffled tank agitated by a Rushton turbine at mixing intensity 40 W/m3 and kaolin concentration 0.44 g/l. The tests were carried out with a model wastewater (a suspension of tap water and kaolin). The model wastewater was flocculated with organic Sokoflok 56 A flocculant (solution 0.1 % wt.). The flock size and flock shape were investigated by image analysis. A simple semiempirical generalized correlation for flock growth kinetics was proposed, and was used for data treatment. The flock shape was characterized by fractal dimension Df2. Using the statistical hypothesis test, the fractal dimension was found to be independent of flocculation time, and the value Df2 = 1.442 ± 0.125 was determined as the average value for the given conditions.