Search results for "Temperature gradient"
showing 10 items of 73 documents
In-flight temperature of solid micrometric powders during cold spray additive manufacturing
2020
Abstract During cold dynamic gas spray additive manufacturing, the thermal field within particles is generally simplified by a state of an instantaneous uniform distribution over the particle's media at any position inside and outside the De-Laval nozzle. This paper addresses critical discussions using analytical and computational analysis of the transient heat transfer within the solid particles due to the convective exchange with the flowing gas. An analytical criterion depicts conditions of instantaneous uniform temperature over the range of typical cold spray data including various particle thermal conductivity, particle size range, dragging velocities, gas nature and gas setting condit…
Onset of convection in a vertical porous cylinder with a permeable and conducting side boundary
2015
Abstract The onset of natural convection in a vertical porous cylinder saturated by a fluid is studied. The lateral confinement of the porous cylinder is due to an external porous medium having a permeability much smaller than that of the cylinder. Thus, the vertical side boundary of the cylinder is permeable and constrained by given pressure and temperature distributions. The lower and upper plane boundaries of the cylinder are impermeable walls. The lower wall is subject to a uniform heat flux, while the upper wall has a uniform temperature. The basic motionless state displays a uniform and vertical temperature gradient oriented downward. The linear stability analysis is carried out by us…
Spatial and temporal changes in Actinobacterial dominance in experimental artificial groundwater recharge.
2008
Abstract Artificial groundwater recharge (AGR) is used in the drinking water industry to supplement groundwater resources and to minimise the use of chemicals in water treatment. This study analysed the spatial and temporal changes of microbial communities in AGR using two test systems: a nutrient-amended fluidized-bed reactor (FBR) and a sand column. Structural changes in the feed lake water (Lake Roine), FBR, and sand column bacterial communities were determined by denaturing gradient gel electrophoresis (DGGE) and the length heterogeneity analysis of amplified 16S rRNA genes (LH-PCR). Two clone libraries were created to link the LH-PCR results to the dominant bacterial groups. The lake w…
In situ synchrotron characterization of mechanically activated self-propagating high-temperature synthesis applied in Mo–Si system
1999
Abstract An original experiment was designed to monitor structural and thermal evolutions during the MASHS (Mechanically Activated Self-propagating High-temperature Synthesis) process in the Mo–Si system. Time-Resolved X-Ray Diffraction (TRXRD) coupled with an infrared imaging technique was performed to study, in situ, the formation of the α-MoSi2 phase in the combustion front. Despite a temporal resolution of 50 ms between two consecutive diffractograms, no intermediate phase was observed during the passage of the combustion front. The only reaction responsible for the self-sustentation is Mo+2Si→MoSi2 in the primary zone inside the combustion wave. The mechanical activation was found to i…
Molecular tools to assess the diversity and density of denitrifying bacteria in their habitats
2007
Publisher Summary This chapter describes the molecular tools to assess the diversity and density of denitrifying bacteria in their habitats. Genome sequencing and metagenomic projects might even provide new denitrification gene sequences, which could aid in designing more broad range primers. Most information is obtained by cloning and sequencing the polymerase chain reaction (PCR) amplicons, but a more rapid analysis is achieved using fingerprinting techniques. As all PCR-based analyses, the fingerprinting techniques are subjected to well-known biases introduced by, e.g., DNA extraction procedures, primer selection, and PCR conditions. For denitrifiers, the PCR-RFLP (restriction fragment l…
Mass transfer in nonisothermal ferrocolloids under the effect of a magnetic field
1999
Abstract The paper presents a review of newest experimental results on particle thermal diffusion in hydrocarbon based ferrofluids. The measurements are performed using a vertical thermal diffusion column, the Soret coefficient is evaluated from particle separation curves employing a simple column theory which accounts for thermal convection in the vertical channel forced by a concentration buoyancy force arising during the thermophoretic transfer of heavy particles. High positive values of the Soret coefficient of lyophilized Fe 3 O 4 and Mn x Zn 1− x Fe 2 O 4 particles in surfacted tetradecane based colloids are measured. Experiments confirm the theoretically predicted anisotropy of parti…
Magnetically enhancing the Seebeck coefficient in ferrofluids.
2019
The influence of the magnetic field on the Seebeck coefficient (Se) was investigated in dilute magnetic nanofluids (ferrofluids) composed of maghemite magnetic nanoparticles dispersed in dimethyl-sulfoxide (DMSO). A 25% increase in the Se value was found when the external magnetic field was applied perpendicularly to the temperature gradient, reminiscent of an increase in the Soret coefficient (ST, concentration gradient) observed in the same fluids. In-depth analysis of experimental data, however, revealed that different mechanisms are responsible for the observed magneto-thermoelectric and -thermodiffusive phenomena. Possible physical and physico-chemical origins leading to the enhancemen…
Soret coefficient of nanoparticles in ferrofluids in the presence of a magnetic field
1998
Experiments on a nonstationary separation of nanometer-sized Mn0.5Zn0.5Fe2O particles of hydrocarbon-based ferrocolloids in a flat vertical thermal diffusion column are performed. By using a modified separation theory which accounts for a one-dimensional mixed (thermal and concentration) convection in the column, the Soret coefficient of lyophilized nanoparticles from the separation curves are calculated. It is shown that in a zero magnetic field particles are transferring toward decreasing temperatures. The thermal diffusion ratio αT reaches a value αT≈+20. A significant influence of a uniform magnetic field B on particle separation is observed. If B is oriented along the temperature gradi…
Route to chaos in the weakly stratified Kolmogorov flow
2019
We consider a two-dimensional fluid exposed to Kolmogorov’s forcing cos(ny) and heated from above. The stabilizing effects of temperature are taken into account using the Boussinesq approximation. The fluid with no temperature stratification has been widely studied and, although relying on strong simplifications, it is considered an important tool for the theoretical and experimental study of transition to turbulence. In this paper, we are interested in the set of transitions leading the temperature stratified fluid from the laminar solution [U∝cos(ny),0, T ∝ y] to more complex states until the onset of chaotic states. We will consider Reynolds numbers 0 < Re ≤ 30, while the Richardson numb…
Orthogonal electrophoretic fractionation of DNA in agarose gels.
2008
We developed an electrophoretic procedure, using Voltage Gradient Gel Electrophoresis (VGGE), which allows to obtain both an improvement of the resolution power of the system in orthogonal fractionation of DNA and, mainly, an about fourfold enhancement of hybridization signals in Southern blotting applications.