Pulling of glass microcapillaries: Theory and experiment

An approximate analytical solution is obtained which predicts a microcapillary form during pulling which is close to that observed in experiments.Institute of Mechanics and Biomechanics, Bulgarian Academy of Sciences, Sofia. Insitute for Problems of Mechanics, Russian Academy of Sciences, Moscow. Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 63, No. 6, pp. 722–727, December, 1992.Indices 0, p, and 1 denote R, h, and T referring to the initial section (x=0), heating zone boundary (x=l), and fiber section on the receiving device (x=L).     

Oblique penetration of a rigid projectile into an elastic-plastic target

The main objective of the present work is to develop an approximate solution of the problem of oblique penetration of a rigid projectile into an elastic-plastic target of finite thickness. This is accomplished by generalizing the work on normal penetration reported in [1]. Here, an irrotational isochoric velocity field is considered that consists of three parts, each of which together satisfy the condition of impenetrability at the projectile's surface. The first part is associated with the longitudinal motion of the projectile, the second part with the transverse motion, and the third part with the projectile rotation in the plane defined by the initial longitudinal projectile velocity and the normal to the target surface. The target material is assumed to be incompressible and the target region is subdivided into an elastic region ahead of the projectile, and a rigid-plastic region near the projectile. Using the above potential velocity field, inertia effects are included and the linear momentum equation is solved exactly in the elastic region. In the plastic region, the linear momentum equation is integrated numerically along the instantaneous streamlines to determine the pressure field on the projectile surface. Then the decelerating force and moment applied to the projectile are solved numerically. The model developed here predicts the residual velocity, the ballistic limit, as well as the residual angle of obliquity. Moreover, this model is able to describe the phenomenon of ricochet. It is shown that the agreement of the theory with experiments is good even though no adjustable parameters are used. Also, a user-friendly computer program has been developed that is available for distribution along with a Users' Manual.     

The theory of bubble combustion reactors

We have proposed a mathematical model of the combustion of bubble reactive media in which the heat of the reaction is initially expended on the heating of a vapor-gas mixture contained within bubbles, and then the fluid is transferred through the interphase surface, as a consequence of which the fluid becomes heated and vaporizes. Under certain assumptions (a low volumetric gas-phase content, intensive mixing of the original components and the final products, quasiequilibrium of the vapor-formation process) we have derived approximate analytical expressions for the heat-release and heat-transfer functions, and we have solved numerically the heat-balance equation. We have investigated the possible combustion regimes and have determined the regions in which the steady state exists.Ukhta. Translated from Fizika Goreniya i Vzryva, No. 2, pp. 66–75, March–April, 1991.     

Fluid flow in micro-channels

We consider the problem of liquid and gas flow in micro-channels under conditions of a small Knudsen and Mach numbers, that correspond to continuum model. Data from the literature on pressure drop in circular, rectangle, triangular and trapezoidal micro-channels with hydrodynamic diameter ranging from 1.01 μm to 4010 μm are analyzed. The Reynolds number at transition from laminar to turbulent flow is considered. Attention is paid to comparison between predictions of the conventional theory and experimental data, obtained during the last decade, as well as to discussion of possible sources of unexpected effects which were revealed by a number of previous investigations.     

Self‐Healing Reduced Graphene Oxide Films by Supersonic Kinetic Spraying

The industrial scale application of graphene and other functional materials in the field of electronics has been limited by inherent defects, and the lack of simple deposition methods. A simple spray deposition method is developed that uses a supersonic air jet for a commercially available reduced graphene oxide (r‐GO) suspension. The r‐GO flakes are used as received, which are pre‐annealed and pre‐hydrazine‐treated, and do not undergo any post‐treatment. A part of the considerable kinetic energy of the r‐GO flakes entrained by the supersonic jet is used in stretching the flakes upon impact with the substrate. The resulting “frozen elastic strains” heal the defects (topological defects, namely Stone‐Wales defect and C₂ vacancies) in the r‐GO flakes, which is reflected in the reduced ratio of the intensities of the D and G bands in the deposited film. The defects can also be regenerated by annealing.     

Vortex motion in dilute polymer solutions

Vortex-dynamic equations have been derived and applied to two problems concerning annular vortices.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 2, pp. 222–229, August, 1987.     

Heat transfer in micro-channels: Comparison of experiments with theory and numerical results

This paper considers experimental and theoretical investigations on single-phase heat transfer in micro-channels. It is the second part of general exploration “Flow and heat transfer in micro-channels”. The first part discussed several aspects of flow in micro-channels, as pressure drop, transition from laminar to turbulent flow, etc. [G. Hetsroni, A. Mosyak, E. Pogrebnyak, L.P. Yarin, Fluid flow in micro-channels, Int. J. Heat Mass Transfer 48 (2005) 1982–1998]. In this paper, the problem of heat transfer is considered in the frame of a continuum model, corresponding to small Knudsen number. The data of heat transfer in circular, triangular, rectangular, and trapezoidal micro-channels with hydraulic diameters ranging from 60 μm to 2000 μm are analyzed. The effects of geometry, axial heat flux due to thermal conduction through the working fluid and channel walls, as well as the energy dissipation are discussed. We focus on comparing experimental data, obtained by number of investigators, to conventional theory on heat transfer. The analysis was performed on possible sources of unexpected effects reported in some experimental investigations.