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This chapter discusses the four main types of microorganisms that are used for the production of biodiesel: bacteria, yeast, fungi, and microalgae. Oleaginous microorganisms, that is, yeast, filamentous fungi, and microalgal species, are very interesting organisms that are able to accumulate lipids at levels greater than 20" of their cellular dry weight. Microorganisms have long been used in industrial processes, starting with alcohol fermentation using Saccharomyces cerevisiae. Microalgae are rich in some products, such as pigments and chlorophyll, which make them particularly attractive for other applications, like cosmetics, pharmaceuticals, and food. Microalgae can be classified into four main classes: diatoms, green algae, blue-green algae, and golden algae. Single-cell oils are lipids that are extracted from unicellular microorganisms. The oil extraction and purification of single cell oils still represent major costs in the production process. It is therefore important to have efficient downstream processing.

Liquid layers evaporating under the influence of a gas shear flow presents a non-uniform distribution of the evaporation rate all along the interface. Being the evaporation an endothermic process, a thermal gradient along the interface is generated and thermo-capillary flows are induced. Hence, two opposite mechanisms regulate the movement of the interface: the shear stress of the gas that entrains the interface in the direction of the flow and the thermo-capillary stress that forces the interface to move against the flow direction. The composition of these mechanisms at the interface generates an unstable thermal patterning. The dynamic evolution of the patterning and the relative evaporation rate are strongly influenced by the flow rate of inert gas, the layer thickness and the liquid thermo-physical properties. The goal of the present work is to study numerically how the evaporation process is influenced by the above-mentioned mechanisms. The focus will be on the evolution of the thermal patterning at the interface and the assessment of the main factors influencing the computed evaporation rate.

In this work a supercritical technology is proposed to improve the classical emulsification/diffusion technology for lipid nanoparticles (LNs) production. The process is based on the emulsion diffusion method improved by the addition of a continuous supercritical fluid processing step to eliminate the organic solvent from the nanosuspension obtained. Different emulsion/diffusion formulations for stearic acid nanoparticles production were tested and, then, processed by supercritical continuous extraction at 80 bar and 45 °C (liquid/gas ratio of 0.1) in a packed column, obtaining an efficient benzyl alcohol elimination. Solvent residues less than 100 ppm were measured. Stearic acid nanoparticles were not extracted or damaged by the supercritical processing step, did not stick on the packing elements and showed mean diameters of 30–50 nm; a value of one order of magnitude smaller than the ones obtained by the conventional emulsion/diffusion technology with a recovery efficiency of 100%. Indeed, the fast and complete elimination of the benzyl alcohol around the nanoparticles reduced the aggregation phenomena responsible of larger lipid particle sizes obtainable by traditional process.

A mini splitterless-split-flow thin fractionation (SPLITT) device has been developed to achieve fast separations of micrometer-sized species. In this device, inlet and outlet steps have replaced the splitters, which are common to conventional SPLITT channels. By elimination of the splitters, it becomes straightforward to reduce channel dimensions while maintaining the classic method of fabrication. Reduced dimension channels allow high axial velocity at relatively low flow rate. These high axial velocities generate an enhancement of inertial lift forces and hydrodynamic shear-induced diffusion. Experiments carried out with particulate and biological species in a mini step-SPLITT channel demonstrate that these hydrodynamic effects yield highly enriched fractions of smaller species from binary mixtures.

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or "nanofluids," was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (�10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise. � 2009 American Institute of Physics.

The evolution of convective patterns arising in evaporating liquid layers subject to a flow of inert gas depends on dynamical, thermo-physical and geometrical parameters. To the first group it is possible to associate the average velocity of the inert gas current and the total pressure of the gas phase — inert gas and vapor — insisting on the evaporating layer. The volatile liquid is also of importance in the convective patterns selection especially for what concerns the values of the latent heat of evaporation and of the cinematic viscosity. In this paper, we will focus on the influence that the lateral boundaries of the liquid pool have in the pattern selection process from the numerical point of view. A particular emphasis will be given to the heat transfer characteristics and to their dependence from both the liquid layer depth and the size of the evaporating surface.Copyright © 2008 by ASME

When a layer of volatile liquid is subject to a flow of inert gas, a non-uniform distribution of the evaporation rate is generated all along the interface. Being evaporation stronger at the inlet boundary of the layer, because of the maximal efficiency of the inert gas flow in removing vapor from the interface, a thermal gradient along the interface is generated. Two opposite mechanisms regulate the movement of the interface: the shear stress of the gas that entrains the interface in the direction of the flow and the thermo-capillary stress that forces the interface to move against the flow direction. Moreover, because of the overall cooling of the interface due to the evaporative process, a gradient normal to the interface is also created. It results in a potentially unstable situation that is strongly influenced by the flow rate of inert gas, the layer thickness and the liquid thermo-physical properties. The goal of the present work is to study numerically if and how the dynamic evolution of the liquid layer is driven by the above-mentioned mechanisms. The main results concern the evaluation of the influence of the thermal instability patterns, eventually generated by the concurrent action of non-uniform evaporation and thermo-capillary motion, on the heat transfer at the bottom liquid. The distribution of temperature and velocity in the gas and liquid bulk phase for different mass flow rate of inert gas has also been of interest.Copyright © 2007 by ASME