Thermosolutal LTNE Porous Mixed Convection Under the Influence of the Soret Effect

The effects of horizontal pressure gradient and Soret coefficient on the onset of double-diffusive convection in a fluid-saturated porous layer under the influence of local thermal nonequilibrium (LTNE) temperatures are analyzed. Darcy's law with local acceleration term, which involves the two-field temperature model describing the fluid and solid phases separately and the approximation of Oberbeck-Boussinesq, is used. The dynamics of small-amplitude perturbations on the basic mixed convection flow is studied numerically. Using the Galerkin method along with the QZ-algorithm, the eighth order eigenvalue differential equation obtained by employing linear stability analysis is solved. The solution provides the neutral stability curves and determines the threshold of linear instability, and the critical values of thermal Darcy-Rayleigh number, wave number, and the frequency at the onset of instability are determined for various values of control parameters. It is found that, rather than the stationary motion, the instability is found to be via oscillatory motion. Besides, the contribution to each parameter on stability characteristics is explored in detail, and some relevant findings have been described that have not been reported hitherto in the literature.

Self-thermophoresis of laser-heated spherical Janus particles

An analytic framework is presented for calculating the self-induced thermophoretic velocity of a laser-heated Janus metamaterial micro-particle, consisting of two conducting hemispheres of different thermal and electric conductivities. The spherical Janus is embedded in a quiescent fluid of infinite expanse and is exposed to a continuous light irradiation by a defocused laser beam. The analysis is carried under the electrostatic (Rayleigh) approximation (radius small compared to wavelength). The linear scheme for evaluating the temperature field in the three phases is based on employing a Fourier–Legendre approach, which renders rather simple semi-analytic expressions in terms of the relevant physical parameters of the titled symmetry-breaking problem. In addition to an explicit solution for the self-thermophoretic mobility of the heated Janus, we also provide analytic expressions for the slip-induced Joule heating streamlines and vorticity field in the surrounding fluid, for a non-uniform (surface dependent) Soret coefficient. For a ‘symmetric’ (homogeneous) spherical particle, the surface temperature gradient vanishes and thus there is no self-induced thermophoretic velocity field. The ‘inner’ temperature field in this case reduces to the well-known solution for a laser-heated spherical conducting colloid. In the case of a constant Soret phoretic mobility, the analysis is compared against numerical simulations, based on a tailored collocation method for some selected values of the physical parameters. Also presented are some typical temperature field contours and heat flux vectors prevailing in the two-phase Janus as well as light-induced velocity and vorticity fields in the ambient solute and a new practical estimate for the self-propelling velocity. Graphic abstract

The Soret coefficients of the ternary system water/ethanol/triethylene glycol and its corresponding binary mixtures

Thermodiffusion in ternary mixtures is considered prototypic for the Soret effect of truly multicomponent systems. We discuss ground-based measurements of the Soret coefficient along the binary borders of the Gibbs triangle of the highly polar and hydrogen bonding ternary DCMIX3-system water/ethanol/triethylene glycol. All three Soret coefficients decay with increasing concentration, irrespective of the choice of the independent component, and show a characteristic sign change as a function of temperature and/or composition. With the exception of triethylene glycol/ethanol at high temperatures, the minority component always migrates toward the cold side. All three binaries exhibit temperature-independent fixed points of the Soret coefficient. The decay of the Soret coefficient with concentration can be related to negative excess volumes of mixing. The sign changes of the Soret coefficients of the binaries allow to draw far-reaching conclusions about the signs of the Soret coefficients of the corresponding ternary mixtures. In particular, we show that at least one ternary composition must exist, where all three Soret coefficients vanish simultaneously and no steady-state separation is observable. Graphic abstract

Temperature profile characterization with fluorescence lifetime imaging microscopy in a thermophoretic chip

This study introduces a thermophoretic lab-on-a-chip device to measure the Soret coefficient. We use resistive heating of a microwire on the chip to induce a temperature gradient, which is measured by fluorescence lifetime imaging microscopy (FLIM). To verify the functionality of the device, we used dyed polystyrene particles with a diameter of 25 nm. A confocal microscope is utilized to monitor the concentration profile of colloidal particles in the temperature field. Based on the measured temperature and concentration differences, we calculate the corresponding Soret coefficient. The same particles have been recently investigated with thermal diffusion forced Rayleigh scattering (TDFRS) and we find that the obtained Soret coefficients agree with literature results. This chip offers a simple way to study the thermophoretic behavior of biological systems in multicomponent buffer solutions quantitatively, which are difficult to study with optical methods solely relying on the refractive index contrast. Graphic abstract

Soret and Diffusion Coefficients Measurement for Binary and Ternary Mixtures on Board the International Space Station Using SODI Apparatus

Thermodiffusion or Soret effect is a heat and mass transfer phenomenon in a non-isothermal liquid and gas mixtures. This phenomenon is more pronounced in oil fields, usually due to the porous environment. A precise and better understanding of the thermodiffusion phenomena in multi-component mixtures results in a more accurate modeling of oil reservoirs. Accordingly, the main objective of this study is to investigate the thermodiffusion phenomenon in the multicomponent mixtures. In order to achieve this objective, two series of thermodiffusion experiments conducted on board the International Space Station (ISS) using the SODI (Selectable Optical Diagnostics Instrument) facility were analyzed. The first series of experiments aimed to study the effects of the forced vibration on the Soret phenomena. The experimental mixture was water and isopropanol with different compositions subjected to various temperature gradients normal to the vibrations. Results revealed maximum separation for the case with the minimum vibration and the lower temperature gradient; however, a linear relationship between Gershuni number and maximum separation was not found. On the other hand, the second series of experiment was aimed to the measurement of the diffusion coefficients of selected ternary mixtures. Mixtures of tetrahydronaphthalene-isobutylbenzene-dodecane at five different compositions were hosted in the DSC (Diffusion and Soret Coefficient) cell array. Thus, the Soret diffusion coefficients and the molecular diffusion coefficients of the mentioned hydrocarbon mixture at five different compositions have been reported. To process the results of these experiments an advance image processing technique was developed and implemented in an application with GUI (Graphical User Interface) for the Mach-Zehnder interferometer (MZI). Then, the application of the windowed Fourier transformation (WFT) to analyze the heat and mass transfer problem using the MZI setup is proposed. Results show that the WFT noticeably improves the measurement of concentration. This improvement is more evident for the ternary. It was shown that about 10% underestimation of the Soret coefficient would be resulted; if an accurate determination of the thermal time for the MZI is not used. The reliability and the repeatability of the MZI apparatus on board ISS to study thermodiffusion for binary and ternary mixtures were shown.

Soret and Diffusion Coefficients Measurement for Binary and Ternary Mixtures on Board the International Space Station Using SODI Apparatus

Thermodiffusion or Soret effect is a heat and mass transfer phenomenon in a non-isothermal liquid and gas mixtures. This phenomenon is more pronounced in oil fields, usually due to the porous environment. A precise and better understanding of the thermodiffusion phenomena in multi-component mixtures results in a more accurate modeling of oil reservoirs. Accordingly, the main objective of this study is to investigate the thermodiffusion phenomenon in the multicomponent mixtures. In order to achieve this objective, two series of thermodiffusion experiments conducted on board the International Space Station (ISS) using the SODI (Selectable Optical Diagnostics Instrument) facility were analyzed. The first series of experiments aimed to study the effects of the forced vibration on the Soret phenomena. The experimental mixture was water and isopropanol with different compositions subjected to various temperature gradients normal to the vibrations. Results revealed maximum separation for the case with the minimum vibration and the lower temperature gradient; however, a linear relationship between Gershuni number and maximum separation was not found. On the other hand, the second series of experiment was aimed to the measurement of the diffusion coefficients of selected ternary mixtures. Mixtures of tetrahydronaphthalene-isobutylbenzene-dodecane at five different compositions were hosted in the DSC (Diffusion and Soret Coefficient) cell array. Thus, the Soret diffusion coefficients and the molecular diffusion coefficients of the mentioned hydrocarbon mixture at five different compositions have been reported. To process the results of these experiments an advance image processing technique was developed and implemented in an application with GUI (Graphical User Interface) for the Mach-Zehnder interferometer (MZI). Then, the application of the windowed Fourier transformation (WFT) to analyze the heat and mass transfer problem using the MZI setup is proposed. Results show that the WFT noticeably improves the measurement of concentration. This improvement is more evident for the ternary. It was shown that about 10% underestimation of the Soret coefficient would be resulted; if an accurate determination of the thermal time for the MZI is not used. The reliability and the repeatability of the MZI apparatus on board ISS to study thermodiffusion for binary and ternary mixtures were shown.

Experimental measurement of Soret coefficient and numerical study on effect of g-jitter in liquid mixtures

Experimental measurement of Soret coefficient and numerical study on effect of g-jitter in liquid mixtures

Experimental measurement of Soret coefficient and numerical study on effect of g-jitter in liquid mixtures

Experimental measurement of Soret coefficient and numerical study on effect of g-jitter in liquid mixtures

Effect of micro vibration from two space platform on liquid mixture during thermodiffusion experiment

In the present study, a two-dimensional numerical simulation was carried out for binary mixture. The influence of micro gravity vibration or acceleration on board Iinternational Space Station and FOTON-M3, influence of different cavities size as well as the effect of the sign of the Soret coefficient (fluid flow, heat and mass transfer and concentration) in the solvent were investigated in detail. It must be noted that based on previous experiences with this investigation using the same mixture and cavity by Saghir and Parsa [