Second All-Union Seminar on Hydromechanics and Heat and Mass Exchange in Weightlessness, summaries of reports

Abstracts of reports are given which were presented at the Second All Union Seminar on Hydromechanics and Heat-Mass Transfer in Weightlessness. Topics include: (1) features of crystallization of semiconductor materials under conditions of microacceleration; (2) experimental results of crystallization of solid solutions of CDTE-HGTE under conditions of weightlessness; (3) impurities in crystals cultivated under conditions of weightlessness; and (4) a numerical investigation of the distribution of impurities during guided crystallization of a melt

Long-Wave Instability of Advective Flows in Inclined Layer with Solid Heat Conductive Boundaries

We investigate the stability of the steady convective flow in a plane tilted layer with ideal thermal conductivity of solid boundaries in the presence of uniform longitudinal temperature gradient. Analytically found the stability boundary with respect to the long-wave perturbations, find the critical Grashof number for the most dangerous among them of even spiral perturbation.Comment: in Russian, 18 pages, 5 figures, submited to Appl. mechanics and physics, RAS Siberian brunch, Novosibirsk, Russia; Key words: advective flow, oblique layer, a longitudinal temperature gradient, long-wave instabilit

Buoyant-thermocapillary instabilities of differentially heated liquid layers

URL: http://www-spht.cea.fr/articles/T95/103 Instabilités d'écoulements thermocapillaires en présence de gravitéInternational audienceThe stability of buoyant-thermocapillary-driven flows in a fluid layer subjected to a horizontal temperature gradient is analysed. Our purpose is the modelization of recent experimental results obtained for a fluid of Prandtl number Pr=7, by Daviaud and Vince [Phys. Rev. E, 4432 (1993)] who observed a transition between traveling waves and stationary rolls when the height of fluid is increased. Our model takes into account several effects which were examined separately in previous studies. The relative importance of buoyancy and thermocapillarity is controlled by the ratio W of Marangoni number to Rayleigh number. The fluid layer is bounded below by a rigid plane whose temperature varies linearly along the direction of the thermal gradient. A Biot number is introduced to describe heat transfer at the top free surface. Our stability analysis establishes the existence of a transition between stationary and oscillatory modes when W exceeds a value ${\rm W}_0$ which is function of the Biot number. Moreover, two types of oscillatory modes have been identified which differ by the range of variation of their critical parameters (wave number, frequency, angle of propagation) versus W

Adrenal myelolipoma: Operative indications and outcomes

Background: Adrenal myelolipoma (AM) is a benign lesion for which adrenalectomy is infrequently indicated. We investigated operative indications and outcomes for AM in a large single-institution series. Subjects and Methods: A retrospective cohort study of prospectively collected data was conducted. Patients (≥16 years of age) who underwent adrenalectomy in the Division of General Surgery at Barnes-Jewish Hospital (1993–2010) were grouped by operative indication (myelolipoma versus other pathology) and compared using nonparametric tests (α<0.05). Results: Sixteen patients (4.0%) had myelolipomas resected out of 402 patients who underwent adrenalectomy. Fourteen patients with suspected AM underwent adrenalectomy, 13 (93%) of whom had AM confirmed on pathology. Indications for adrenalectomy were abdominal or flank pain, large tumor size (>8 cm), atypical radiologic appearance, and/or inferior vena cava compression. Three patients with suspected other adrenal lesions had AM confirmed on final pathology. Operative approach was laparoscopic in 15 cases and open in 1 case of a 21-cm lesion. Patients who underwent laparoscopic adrenalectomy for AM (n=15) or other adrenal pathology (n=343) were similar with respect to age, gender, American Society of Anesthesiologists classification, prior abdominal operation, tumor side, operative time, conversion rate, estimated blood loss, intraoperative complications, hospital length of stay, and 30-day morbidity. However, patients with resected AM had a higher body mass index (36.5±8.1 kg/m(2) versus 30.1±7.5 kg/m(2); P<.01) and a larger preoperative tumor size (8.4±3.0 cm versus 3.1±1.7 cm; P<.01). Conclusions: Laparoscopic adrenalectomy may be appropriate for patients with a presumptive diagnosis of AM and abdominal or flank pain, large tumor size, and/or uncertain diagnosis after imaging. Outcomes and morbidity following LA for AM and other adrenal pathology appear comparable

A summary of new predictive high frequency thermo-vibrational models in porous media

In this chapter, we consider the effect of mechanical vibration on the onset of convection in porous media. The porous media is saturated either by a pure fluid or by a binary mixture. The importance of transport model on stability diagrams are presented and discussed. The stability threshold for the Darcy-Brinkman case in the RaTc-R and kc-R diagrams are presented (where RaTc, kc and R are the critical Rayleigh number, the critical wave number and the vibration parameters respectively). It is shown that there is a significant deviation from the Darcy model. In the thermo-solutal case with the Soret effect, the influence of vibration on the reduction of multi-cellular convection is emphasized. A new analytical relation for obtaining the threshold of mono-cellular convection is derived. This relation shows how the separation factor Ψ is related to controlling parameters of the problem, Ψ = f (R, ε*, Le) when the wave number k -> 0. The importance of vibrational parameter definition is highlighted and it is shown how, by using a proper definition for vibrational parameter, we may obtain compact relationship. It is also shown how this result may be used to increase components separation

Convection in nanofluids with a particle-concentration-dependent thermal conductivity

Thermal convection in nanofluids is investigated by means of a continuum model for binary-fluid mixtures, with a thermal conductivity depending on the local concentration of colloidal particles. The applied temperature difference between the upper and the lower boundary leads via the Soret effect to a variation of the colloid concentration and therefore to a spatially varying heat conductivity. An increasing difference between the heat conductivity of the mixture near the colder and the warmer boundary results in a shift of the onset of convection to higher values of the Rayleigh number for positive values of the separation ratio psi>0 and to smaller values in the range psi<0. Beyond some critical difference of the thermal conductivity between the two boundaries, we find an oscillatory onset of convection not only for psi<0, but also within a finite range of psi>0. This range can be extended by increasing the difference in the thermal conductivity and it is bounded by two codimension-2 bifurcations.Comment: 13 pages, 11 figures; submitted to Physical Review

Particle entrapment as a feedback effect

We consider a suspension of polarizable particles under the action of traveling wave dielectrophoresis (DEP) and focus on particle induced effects. In a situation where the particles are driven by the DEP force, but no external forces are exerted on the fluid, the joint motion of the particles can induce a steady fluid flow, which leads to particle entrapment. This feedback effect is proven to be non-negligible even for small volume concentration of particles.Comment: 4 pages, 4 figures, submitte

Capture of particles of dust by convective flow

Interaction of particles of dust with vortex convective flows is under theoretical consideration. It is assumed that the volume fraction of solid phase is small, variations of density due to nonuniform distribution of particles and those caused by temperature nonisothermality of medium are comparable. Equations for the description of thermal buoyancy convection of a dusty medium are developed in the framework of the generalized Boussinesq approximation taking into account finite velocity of particle sedimentation. The capture of a cloud of dust particles by a vortex convective flow is considered, general criterion for the formation of such a cloud is obtained. The peculiarities of a steady state in the form of a dust cloud and backward influence of the solid phase on the carrier flow are studied in detail for a vertical layer heated from the sidewalls. It is shown that in the case, when this backward influence is essential, a hysteresis behavior is possible. The stability analysis of the steady state is performed. It turns out that there is a narrow range of governing parameters, in which such a steady state is stable.Comment: 14 pages, 10 figures, published in Physics of Fluid