5,726 research outputs found
Study of a laminar falling film flowing over a wavy wall column: Part II. Experimental validation of hydrodynamic model
The interface position of a film flowing over a wavy wall column is experimentally studied by an optical method
composed of a charge coupled device (CCD) video camera. The results are compared with theoretical calculations and
show a good agreement between results for both the film thickness and the vortex position. However, there exist some
discrepancies because the interface is travelled by waves not accounted for in the mathematical model as it is supposed to be flat. Some characteristics of the waves are experimentally noted. Furthermore, the in¯uence of the viscosity on the film thickness is established as well
Modelling of the coupling hydrodynamic transfer for a gas-liquid countercurrent flow on a wavy surface
This paper concerns laminar countercurrent gas–liquid flow over a wavy wall column, in the case of a falling liquid film. The modelling concerns the coupling of hydrodynamic and heat and mass transfer for an absorption as an example of application. The falling liquid film interacts, through the free interface, with the gas phase. The wavy surface generates particular hydrodynamic conditions with the presence of a vortex in both phases. The consequence of these vortices is an increase of transfers compared to the smooth wall
Effect of fingerprints orientation on skin vibrations during tactile exploration of textured surfaces
In humans, the tactile perception of fine textures is mediated by skin
vibrations when scanning the surface with the fingertip. These vibrations are
encoded by specific mechanoreceptors, Pacinian corpuscules (PCs), located about
2 mm below the skin surface. In a recent article, we performed experiments
using a biomimetic sensor which suggest that fingerprints (epidermal ridges)
may play an important role in shaping the subcutaneous stress vibrations in a
way which facilitates their processing by the PC channel. Here we further test
this hypothesis by directly recording the modulations of the
fingerpad/substrate friction force induced by scanning an actual fingertip
across a textured surface. When the fingerprints are oriented perpendicular to
the scanning direction, the spectrum of these modulations shows a pronounced
maximum around the frequency v/lambda, where v is the scanning velocity and
lambda the fingerprints period. This simple biomechanical result confirms the
relevance of our previous finding for human touch.Comment: Addendum to: Scheibert J, Leurent S, Prevost A, Debr\'egeas G. The
role of fingerprints in the coding of tactile information probed with a
biomimetic sensor. Science 2009; 323:1503?6 3 pages, 1 figur
Enhancement of absorption efficiency for a laminar film flow by hydrodynamic conditions generated by a new type of column wall
Anumerical model is developed to quantify the effects of hydrodynamics on heat and mass transfer during an absorption, for a laminar film flowing over awavywall column. First of all, the modelling is written for a singlewave of thewall shape. Then, an experimental set up, composed of aCCDvideo camera, validates this model. Finally, the model is extended to an entire column. The results include a comparison with the simulation of a smooth column having the same geometrical and operating conditions. Thewavy column dissipates more heat through the
wall (43%) due to the presence of a vortex in the furrows. This leads to an increase of the absorptionrate at the interface (10%). Moreover, the wavy column reaches equilibrium more rapidly in spite of a lower mean film temperature
Study of a laminar falling film flowing over a wavy wall column: Part I. Numerical investigation of the flow pattern and the coupled heat and mass transfer
Flow pattern and heat and mass transfer characteristics for a film flowing over a vertical wavy column are numerically investigated in a laminar flow regime. In our approach, the heat and mass transfer coefficients are avoided in order to include hydrodynamics directly in the heat and mass transfer rates. As a consequence the numerical model is decomposed into two steps. Firstly, the flow pattern for a film with a free interface is developed. Secondly, heat and mass transfer are investigated with the incorporation of velocity fields. The heat and mass transfer coefficients increase in laminar flow
Hydrodynamic and mass transfer efficiency of ceramic foam packing applied to distillation.
In addition to a high void volume and specific area, solid foams possess other properties (low density, good thermal, mechanical, electrical, and acoustical behaviour) that make them attractive for applications such as heat exchangers and reformers. Applications using foams as catalysts or structured catalyst supports have demonstrated higher performance than classical catalysts. Several studies have explored the hydrodynamic behaviour of foams in monophasic and counter current systems and have reported very low pressure drops. This paper describes the application of ceramic foam to distillation. The β-SiC foam contains 5 pores per inch (PPI) with a 91% void volume and a surface area of 640 m2/m3. Performance parameters including pressure drop for the dry and wet packing, flooding behaviour, and dynamic liquid hold-up were measured in a column of 150 mm internal diameter. The mass transfer efficiency in terms of the height equivalent to theoretical plate (HETP) was determined by total reflux experiments using a mixture of n-heptane and cyclohexane at atmospheric pressure. The experimental results were used to develop a set of correlations describing pressure drop and liquid hold-up in terms of a dimensionless number. The hydrodynamic performance and mass transfer efficiency were compared with classical packing materials used in distillation
Adhesive contact of model randomly rough rubber surfaces
We study experimentally and theoretically the equilibrium adhesive contact
between a smooth glass lens and a rough rubber surface textured with spherical
microasperities with controlled height and spatial distributions. Measurements
of the real contact area versus load are performed under compression by
imaging the light transmitted at the microcontacts. is found to be
non-linear and to strongly depend on the standard deviation of the asperity
height distribution. Experimental results are discussed in the light of a
discrete version of Fuller and Tabor's (FT) original model (\textit{Proceedings
of the Royal Society A} \textbf{345} (1975) 327), which allows to take into
account the elastic coupling arising from both microasperities interactions and
curvature of the glass lens. Our experimental data on microcontact size
distributions are well captured by our discrete extended model. We show that
the elastic coupling arising from the lens curvature has a significant
contribution to the relationship. Our discrete model also clearly shows
that the adhesion-induced effect on remains significant even for
vanishingly small pull-off forces. Last, at the local asperity length scale,
our measurements show that the pressure dependence of the microcontacts density
can be simply described by the original FT model
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