.
We present the development of a high-pressure apparatus for measurements of diffusion coefficients in supercritical fluids. The Taylor dispersion method has been adapted to conduct experiments at ...the pressures up to 25.0 MPa. In order to test the developed set-up, binary diffusion coefficients
D
at infinite dilution in supercritical carbon dioxide have been measured for a reference system, benzene, at temperatures in the range of 309.50-319.95 K. The effects of flow velocity, number of consecutive injections and absorbance at different wave numbers on the diffusion coefficient have been analysed. The obtained diffusion coefficients are of the order of 10
-8
m
2
/
s
and in excellent agreement with the available literature data.
Graphical abstract
•Metal disk with parameters rp>3mm, zp>3mm, Tp>1300K can be a diesel fuel igniter.•Ignition time delay for a ceramic particle is larger than for a metal particle.•Using a metal particle as a diesel ...fuel igniter leads to heat transfer enhancement.•Ignition does not occur at full immersion of a hot particle into the liquid fuel.
This study is focused on the heat and mass transfer in the complex process of ignition of diesel fuel by a local heat source. The main macroscopic rules governing the ignition of liquid fuel by small steel and ceramic particles heated from 1200K to 1500K are established and reported. The investigated parameters are the ignition time delay for different igniters i.e. with different sizes, temperatures, porosities and thermophysical properties. Physical and mathematical models are elaborated. The experimental results are used to describe the interactions between the local heat source and the liquid fuel. Numerical simulations of heat transfer processes are carried out taking into account the vaporization and the heat production by the oxidation reaction. The border line defining the limit of the stable ignition domain is determined for diesel fuel. Possible modes and mechanisms of ignition under laboratory conditions are established.
We discuss the application of two-wavelength optical methods for the determination of Soret coefficient in ternary mixtures. Though the principle of such an approach was formulated in the literature ...earlier, we have found a significant obstacle to its implementation and suggested a way to circumvent that obstacle. The main target of our approach is the analysis of the compatibility of the matrices of contrast factors (the derivatives of refractive indices with respect to concentrations) with available light sources used for measuring the Soret effect in ternary mixtures. We report on the development of a simple mathematical approach to verify the applicability of the chosen wavelengths for laser diodes to measure transport coefficients for a certain class of ternary mixtures. The approach has been applied to a number of aqueous ternary mixtures: water-ethanol-k-ethyleneglycol, k = mono, di, tri, and water-t-butanol-DMSO) and light sources in the visible λ
1
= 670 nm and infrared λ
2
= 925 nm spectrum. The regions of feasibility/infeasibility of the methods have been revealed for these mixtures.
.
This paper describes the European Space Agency (ESA) experiments devoted to study thermodiffusion of fluid mixtures in microgravity environment, where sedimentation and convection do not affect the ...mass flow induced by the Soret effect. First, the experiments performed on binary mixtures in the IVIDIL and GRADFLEX experiments are described. Then, further experiments on ternary mixtures and complex fluids performed in DCMIX and planned to be performed in the context of the NEUF-DIX project are presented. Finally, multi-component mixtures studied in the SCCO project are detailed.
Graphical abstract
We have determined the Soret (S
T
), diffusion (
D
, and thermodiffusion (D
T
) coefficients in a ternary mixture of tetralin-isobutylbenzene-
n
-dodecane with a composition of 0.80/0.10/0.10 by mass ...fraction at a temperature of 298K. The Soret coefficients were measured in the microgravity experiment DCMIX1 and on the ground by optical digital interferometry (ODI) using two lasers with different wavelengths. The values of the Soret coefficients were determined from the stationary separation of the components using two- and six-parameter fits. The diffusion coefficients were independently measured using the Taylor Dispersion Technique in the ground laboratory, and the thermodiffusion coefficients were derived from known S
T
and matrix
D
. The processing of the data from the DCMIX experiment conducted on the International Space Station is discussed in detail. The multi-user design of the on-board instrument causes perturbations in the component separation. Several recommendations are suggested for improving the quality of the microgravity results. For example, we demonstrated that the tomography reconstruction of the 3-D concentration field allows to restore the underestimated component separation resulting from the spatial non-linearity of the temperature field. Furthermore, to avoid errors in component separation due to mass exchange between the working liquid volume and the expansion volume at the top of the cell, we suggest considering the evolution of the separation only in the lower half of the cell. The results of this study displayed reasonable quantitative agreement between the microgravity and ground experiments.
Graphical abstract
► An oxidation torrefaction kinetics model was developed based on TGA data. ► Sawdust was torrefied in a fluidized bed reactor using oxygen-laden combustion flue gases. ► Torrefied sawdust was ...compressed into pellets of properties similar to regular pellets.
Oxidative torrefaction of sawdust with a carrier gas containing 3–6% O2 was investigated in a TG and a fluidized bed reactor, with the properties of the torrefied sawdust and pellets compared with traditional torrefaction without any O2, as well as the dry raw material. It is found that the oxidative torrefaction process produced torrefied sawdust and pellets of similar properties as normally torrefied sawdust and corresponding pellets, especially on the density, energy consumption for pelletization, higher heating value and energy yield. For moisture absorption and hardness of the torrefied pellets, the oxidative torrefaction process showed slightly poor but negligible performance. Therefore, it is feasible to use oxygen laden combustion flue gases as the carrier gas for torrefaction of biomass. Besides, torrefied sawdust can be made into dense and strong pellets of high hydrophobicity at a higher die temperature than normally used in the production of traditional control pellets.
Torrefaction of sawdust in a fluidized bed reactor Li, Hui; Liu, Xinhua; Legros, Robert ...
Bioresource technology,
January 2012, 2012, 2012-Jan, 2012-01-00, 20120101, Volume:
103, Issue:
1
Journal Article
Peer reviewed
► Sawdust was torrefied in a fluidized bed with an inclined orifice distributor. ► Hydrophobicity of the torrefied sawdust decreased with increasing severity of torrefaction. ► Weight loss, energy ...content and physical properties of the torrefied sawdust are strongly correlated.
In the present work, stable fluidization of sawdust was achieved in a bench fluidized bed with an inclined orifice distributor without inert bed materials. A solids circulation pattern was established in the bed without the presence of slugging and channeling. The effects of treatment severity and weight loss on the solid product properties were identified. The decomposition of hemicelluloses was found to be responsible for the significant changes of chemical, physical and mechanical properties of the torrefied sawdust, including energy content, particle size distribution and moisture absorption capacity. The hydrophobicity of the torrefied sawdust was improved over the raw sawdust with a reduction of around 40wt.% in saturated water uptake rate, and enhanced with increasing the treatment severity due to the decomposition of hemicelluloses which are rich in hydroxyl groups. The results in this study provided the basis for torrefaction in fluidized bed reactors.
With the aim of providing reliable benchmark values, we have measured the Soret, thermodiffusion and molecular diffusion coefficients for the ternary mixture formed by 1,2,3,4-tetrahydronaphthalene, ...isobutylbenzene and
n
-dodecane for a mass fraction of 0.8-0.1-0.1 and at a temperature of 25°C. The experimental techniques used by the six participating laboratories are Optical Digital Interferometry, Taylor Dispersion technique, Open Ended Capillary, Optical Beam Deflection, Thermogravitational technique and Sliding Symmetric Tubes technique in ground conditions and Selectable Optical Diagnostic Instrument (SODI) in microgravity conditions. The measurements obtained in the SODI installation have been analyzed independently by four laboratories. Benchmark values are proposed for the thermodiffusion and Soret coefficients and for the eigenvalues of the diffusion matrix in ground conditions, and for Soret coefficients in microgravity conditions.
Graphical abstract
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