S.A. Novopashin, M.A. Serebryakova, and S.Ya. Khmel
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia E-mail: khmel@itp.nsc.ru
Keywords: magnetic fluid, colloid solution, nanoparticles in carbon coating
Pages: 397–412
This is a review of the current state of research in the field of the methods of magnetic fluid synthesis. It focuses on analysis of the methods that use magnetic nanoparticles in an inert coating.
The possibility to control turbulent incompressible boundary layer using air blowing through a finely perforated wall presenting part of the streamlined flat-plate surface was examined. The control was exercised via an action on the state and characteristics of the near-wall flow exerted by controlled (through variation of external-pressure-flow velocity) blowing of air through an air intake installed on the idle side of the plate. A stable reduction of the local values of skin friction coefficient along the model, reaching 50 % at the end of the perforated area, has been demonstrated. The obtained experimental and calculated data are indicative of a possibility to model the process of turbulent-boundary-layer control by air blowing due to external-flow resources.
N.E. Shishkin
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia E-mail: shishkin@itp.nsc.ru
Keywords: swirled gas film cooling, gas concentration at wall, nonisothermal flows, constrain factor
Pages: 427–433
Experiments were conducted about the effect of height of annular slot on efficiency of film cooling in a tube flow. Nonisothermal nature of flows was modelled by mixing of jets with different densities: air with argon or with helium: the concentration of foreign gas on wall was measured. The influence of nearwall jet swirling and of proportions of densities of gas flows as key factors for laminarization of mixing was considered.
A.G. Laptev and E.A. Lapteva
Kazan State University of Power Engineering, Kazan, Russia E-mail: tvt_kgeu@mail.ru
Keywords: heat transfer, mass transfer, skin friction, roughness, film, coolers, analogy
Pages: 435–440
To determine the coefficients of the heat and mass transfer in the ducts with rough and irrigated walls the de-velopment of the classical hydrodynamic analogy of the momentum, mass, and energy transfer has been continued. The conservation properties of the skin-friction laws with respect to various disturbances are used for this purpose, and the “effective velocity” is found the value of which enables us to correct the hydrodynamic analogy. The examples of computations of the Nusselt, Sherwood, and Stanton numbers are shown for rough ducts, cooler, and film flow in the counter-flow. A comparison with the results of other researchers is given.
Explosive cavitation at the front of a negative-pressure pulse has been studied. Conditions for the emergence of bubbles by the mechanism of homogeneous fluctuation nucleation were identified. Those conditions feature a high rate of the phase transformation, with the vapor formation process being concentrated in time at the instant of attainment of a certain pressure. Under such conditions, the liquid cavitation strength is maximal, and its value can be predicted by the homogeneous nucleation theory. For implementing the regime with high nucleation frequency, a method based on passing a negative-pressure pulse across a region with locally heated liquid was employed. The cavitation kinetics was examined by monitoring the perturbation of the heat flow from a miniature heater. The experimental data were generalized using the theory of explosive vapor formation in shock boiling mode. A method for calculating the cavitation in the regime of the fluctuation emergence of bubbles was approbated.
A.A. Gubaidullin and A.S. Gubkin
Tyumen Branch of the Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Tyumen, Russia Tyumen State University, Tyumen, Russia E-mail: timms@tmn.ru, alexshtil@gmail.com
Keywords: bubble cluster, hydrodynamic interaction of bubbles, heat exchange of a bubble with liquid
Pages: 453–462
Numerical investigation of the collective interaction of bubbles in clusters of different configurations was carried out. The mathematical model was used, which accounted for the compressibility and viscosity of the liquid as well as the hydrodynamic interaction between the bubbles. The heat exchange of gas bubbles with liquid was handled within the framework of a two-temperature scheme. An expression for the heat flux to the bubble unit surface was used, which makes it possible to describe the heat exchange of gaseous bubbles with the liquid in a fairly wide range of the values of the liquid pressures and temperatures. The behavior of an individual bubble in the collective of bubbles at an instantaneous compression and at a periodic disturbance of different frequencies was investigated. It is shown that under certain conditions, considerable compression ratios and, as a consequence, high temperatures and temperatures are reached for some bubbles. The influence of the cluster configuration has been investigated. It is shown by the examples of a cluster of three embedded dodecahedra, linear and stochastic clusters that the configuration of the cluster may affect strongly its dynamics.
We report measurements of two-dimensional (B/D = 5) fully turbulent and developed duct flows (overall length/depth, L/D = 60; D-based Reynolds number Re > 104) for inclinations to 30° from vertical at low voidages (< 5 % sectional average) representative of disperse regime using tap water bubbles (4-6 mm) and smaller bubbles (2 mm) stabilised in ionic solution. Pitot and static probe instrumentation, primitive but validated, provided adequate (10 % local value) discrimination of main aspects of the mean velocity and voidage profiles at representative streamwise station i.e L/D
= 40. Our results can be divided into three categories of behaviour. For
vertical flow (0°) the evidence is inconclusive as to whether bubbles are
preferentially trapped within the wall-layer as found in some, may be most earlier experimental works. Thus, the
4-mm bubbles showed indication of voidage retention but the 2-mm bubbles
did not. For nearly vertical flow (5°) there was pronounced profiling of voidage especially with 4-mm bubbles
but the transverse transport was not suppressed sufficiently to induce any
obvious layering. In this context, we also refer to similarities with previous
work on one-phase vertical and nearly vertical mixed convection flows
displaying buoyancy inhibited mean shear turbulence. However, with inclined
flow (10+ degrees) a distinctively layered pattern was invariably manifested in
which voidage confinement increased with increasing inclination. In this paper
we address flow behavior at near vertical conditions. Eulerian, mixed and VOF
models were used to compute voidage and mean velocity profiles.
A mathematical model was developed for calculation
of steam-water flow in a geothermal well for the feeding interval. The model
assumes a variable mass flow rate over the channel length. The basis for this
model are the flow continuity equation, momentum and energy conservation
equations, taken with account for variable mass flow. The model was implemented as a computer code
suitable for calculation of flow parameters upstream (downward the top level of
the feeding zone). Then this model was applied for wells in the Mutnovskii
geothermal field, this revealed a
geyser-type mechanism of flow instabilities with the pressure oscillation
period about ten minutes. The remedy for these oscillations was
offered.
H. Yan, T. Zhao, X. Li, Ch. Hun
State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian, Liaoning 116024, China
Keywords: gaseous detonation, carbon-encapsulated iron nanoparticles, detonation tube, hydrogen, air
Pages: 495–501
With ferrocene as a precursor, carbon-encapsulated iron nanoparticles are synthesized through detonation of a gas mixture of hydrogen and air in a titanium detonation tube. XRD and TEM characterization shows that a downward trend in the size of particles can be observed with increasing amounts of the precursor. However, no further decrease occurs when the size of nanoparticles reaches approximately ≈40 nm, after which they remain in the range of 30−50nm. The initial temperature of the detonation tube at 353 K is the optimal initial temperature for the synthesis. The average grain size of the synthesized products becomes larger as the temperature of detonation increases.
Z. Zhang, L. Sun, X. Yao, X. Cao
College of Shipbuilding and Ocean Engineering, Harbin Engineering University, 150001 Harbin, China
Keywords: damage characteristics, contact underwater explosion, cylindrical shell, SPH method, water interlayer
Pages: 502–508
In this paper, a modified smoothed particle hydrodynamics (SPH) formula is deduced to solve the problem of interfaces with a high density ratio. Simplified SPH models for single and double cylindrical shells (abbreviated as single-hull and double-hull models, respectively) are established to study shock wave propagation and to conduct the damage analysis. The SPH results for the single-hull model are verified by AUTODYN. In addition, the damage analysis indicates that the single-hull model is damaged more severely than the double-hull model. The inner shell in the double-hull model is protected by a water interlayer.
