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The kinetics of volatile component evaporation from an atomic solution-melt into a gaseous phase has been theoretically studied. The transfer of the volatile substance in the system is considered to be fulfilled by the diffusion m...
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The kinetics of volatile component evaporation from an atomic solution-melt into a gaseous phase has been theoretically studied. The transfer of the volatile substance in the system is considered to be fulfilled by the diffusion mechanism. The volatile component can evapo- rate either in the atomic form or as diamers. Physical fac- tors limiting the evaporation rate as well as characteristic system parameters have been determined.
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The analysis of Taylor and Batchelor for a single plane screen is extended to the case of any number of arbitrarily-spaced screens of arbitrary pressure drop coefficient, K, with particular attention paid to the effect of removing...
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The analysis of Taylor and Batchelor for a single plane screen is extended to the case of any number of arbitrarily-spaced screens of arbitrary pressure drop coefficient, K, with particular attention paid to the effect of removing non-uniformity in the mean flow. Any spacing will given an attenuation to at least 0.11 provided ΣK exceeds 2.5. Greater attenuation needs more care. The minimum spacing Required for a given attenuation decrease significantly with increasing ΣK. If ΣK exceeds about 4, this minimum depends on only the number Of screens and ΣK. However, measurements show that the degree of uniformity is limited by the velocity overshoot that arises in the vicinity Of the wall boundary layers.
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In a future design of a compact fusion reactor with enhanced power density, how to remove heat from high heat flux components and to get higher temperature operating fluid for power generation will inevitably play an important rol...
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In a future design of a compact fusion reactor with enhanced power density, how to remove heat from high heat flux components and to get higher temperature operating fluid for power generation will inevitably play an important role. In the present work, we propose a new cooling system, using sintered metal porous media. For the purpose of developing this cooling system, heat removal experiments were performed with varying geometrical parameters mainly this time. It is feasible for the proposed cooling system to remove heat flux up to 1.3 MW/m~2 at the present step, and there seems to be a great possibility of the enhancement of the heat removal capacity of this cooling system.
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Air-assisted atomizers in which a thin liquid sheet is deformed under the action of a high-speed air flow are extensively used in industrial applications, e.g., in aircraft turbojet injectors. Primary atomization in these devices ...
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Air-assisted atomizers in which a thin liquid sheet is deformed under the action of a high-speed air flow are extensively used in industrial applications, e.g., in aircraft turbojet injectors. Primary atomization in these devices is a consequence of the onset and growth of instabilities on the air/liquid interfaces. To better understand this process, a temporal linear instability analysis is applied to an thin planar liquid sheet flowing between two semi-infinite streams of a high-speed viscous gas. This study includes the full viscous effects both in the liquid and gas basic states and perturbations. The relevant dimensionless groups entering the non-dimensional Orr-Sommerfeld equations and boundary conditions are the liquid and gas stream Reynolds numbers, the gas to liquid momentum flux ratio, the gas/liquid velocity ratio, the Weber number and the equivalent gas boundary layer to liquid sheet thickness ration. Growth rates and temporal frequencies as a function of the wavenumber, varying the different dimensionless parameters are presented, together with neutral stability curves. From the results of this parametric study it is concluded that when the physical properties of gas and liquid are fixed, the momentum flux ratio is especially relevant to determine the instability condition. It is also observed that the gas boundary layer thickness strongly influences the eave propagation, and acts by damping sheet oscillation frequency and growth. This is especially important because viscosity in the basic gas velocity profile has always been ignored in instability analysis applied to the geometry under study.
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The existence of two-dimensional standing waves on the surface of an infinitely deep perfect fluid under gravity is established. When formulated as a second-order equation for a real-valued function w on the 2-torus and a positive...
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The existence of two-dimensional standing waves on the surface of an infinitely deep perfect fluid under gravity is established. When formulated as a second-order equation for a real-valued function w on the 2-torus and a positive parameter mu, the problem is fully nonlinear (the highest order x-derivative appears in the nonlinear term but not in the linearization at 0) and completely resonant (there are infinitely many linearly independent eigenmodes of the linearization at 0 for all rational values of the parameter mu). Moreover, for any prescribed order of accuracy there exists an explicit approximate solution of the nonlinear problem in the form of a trigonometric polynomial. Using a Nash-Moser method to seek solutions of the nonlinear problem as perturbations of the approximate solutions, the existence question can be reduced to one of estimating the inverses of linearized operators at non-zero points. After changing coordinates these operators become first order and non-local in space and second order in time. After further changes of variables the main parts become diagonal with constant coefficients and the remainder is regularizing, or quasi-one-dimensional in the sense of [22]. The operator can then be inverted for two reasons. First, the explicit formula for the approximate solution means that, restricted to the infinite-dimensional kernel of the linearization at zero, the inverse exists and can be estimated. Second, the small-divisor problems that arise on the complement of this kernel can be overcome by considering only particular parameter values selected according to their Diophantine properties. A parameter-dependent version of the Nash-Moser implicit function theorem now yields the existence of a set of unimodal standing waves on flows of infinite depth, corresponding to a set of values of the parameter mu > 1 which is dense at 1. Unimodal means that the term of smallest order in the amplitude is cos x cos t, which is one of many eigenfunctions of the completely resonant linearized problem.
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Thermal contact resistance is due to imperfect contact of two bodies at the interface. It plays an impor- tant role in the dissipation of heat from electronic devices. The concept of individual heat flux tubes consisting of A sing...
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Thermal contact resistance is due to imperfect contact of two bodies at the interface. It plays an impor- tant role in the dissipation of heat from electronic devices. The concept of individual heat flux tubes consisting of A single contact are and the corresponding gap which Extends far in either solid was used in this study. The three Dimensional conduction equation in the contact region Was solved numerically for different shapes of gap and Contact area and various thermal boundary conditions at Locations far from the contact area. Constricting resistance Defined as the ratio of the temperature difference across The contact surface to the rate of heat transfer through a Heat flux channel was calculated for each case. The results Have indicated that constriction resistance is strongly Affected by the gap geometry, shape of contact area and Certain end surface boundary conditions. The geometry Dependence becomes more significant as the ratio of Contact to total area becomes smaller. Given the fact that The shape of the contact region is highly unpredictable, the Heat flux tube approach can hardly provide a reasonable Estimate of the thermal contact resistance, unless the Geometry of the contact region is properly model.
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Asymptotic behavior of solutions of the compressible Navier-Stokes equations on the half space R-+(n) + ( n >= 2) is considered around a given constant equilibrium. A solution formula for the linearized problem is derived, and L-p...
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Asymptotic behavior of solutions of the compressible Navier-Stokes equations on the half space R-+(n) + ( n >= 2) is considered around a given constant equilibrium. A solution formula for the linearized problem is derived, and L-p estimates for solutions of the linearized problem are obtained for 2 收起
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The purpose of this paper is to demonstrate the effects of thermal expansion, as a result of heat release arising from exothermic chemical reactions, on the underlying turbulent fluid dynamics and its modelling in the case of turb...
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The purpose of this paper is to demonstrate the effects of thermal expansion, as a result of heat release arising from exothermic chemical reactions, on the underlying turbulent fluid dynamics and its modelling in the case of turbulent premixed combustion. The thermal expansion due to heat release gives rise to predominantly positive values of dilatation rate within turbulent premixed flames, which has been shown to have significant implications on the flow topology distributions, and turbulent kinetic energy and enstrophy evolutions. It has been demonstrated that the magnitude of predominantly positive dilatation rate provides the measure of the strength of thermal expansion. The influence of thermal expansion on fluid turbulence has been shown to strengthen with decreasing values of Karlovitz number and characteristic Lewis number, and with increasing density ratio between unburned and burned gases. This is reflected in the weakening of the contributions of flow topologies, which are obtained only for positive values of dilatation rate, with increasing Karlovitz number. The thermal expansion within premixed turbulent flames not only induces mostly positive dilatation rate but also induces a flame-induced pressure gradient due to flame normal acceleration. The correlation between the pressure and dilatation fluctuations, and the vector product between density and pressure gradients significantly affect the evolutions of turbulent kinetic energy and enstrophy within turbulent premixed flames through pressure-dilatation and baroclinic torque terms, respectively. The relative contributions of pressure-dilatation and baroclinic torque in comparison to the magnitudes of the other terms in the turbulent kinetic energy and enstrophy transport equations, respectively strengthen with decreasing values of Karlovitz and characteristic Lewis numbers. This leads to significant augmentations of turbulent kinetic energy and enstrophy within the flame brush for small values of Karlovitz and characteristic Lewis numbers, but both turbulent kinetic energy and enstrophy decay from the unburned to the burned gas side of the flame brush for large values of Karlovitz and characteristic Lewis numbers. The heat release within premixed flames also induces significant anisotropy of sub-grid stresses and affects their alignments with resolved strain rates. This anisotropy plays a key role in the modelling of sub-grid stresses and the explicit closure of the isotropic part of the sub-grid stress has been demonstrated to improve the performance of sub-grid stress and turbulent kinetic energy closures. Moreover, the usual dynamic modelling techniques, which are used for non-reacting turbulent flows, have been shown to not be suitable for turbulent premixed flames. Furthermore, the velocity increase across the flame due to flame normal acceleration may induce counter-gradient transport for turbulent kinetic energy, reactive scalars, scalar gradients and scalar variances in premixed turbulent flames under some conditions. The propensity of counter-gradient transport increases with decreasing values of root-mean-square turbulent velocity and characteristic Lewis number. It has been found that vorticity aligns predominantly with the intermediate principal strain rate eigendirection but the relative extents of alignment of vorticity with the most extensive and the most compressive principal strain rate eigendirections change in response to the strength of thermal expansion.
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We consider the convergence of solutions of conservation laws with viscosity to solutions having shocks of hyperbolic conservation laws without viscosity as the viscosity tends to zero. our analysis reveals a rich structure of non...
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We consider the convergence of solutions of conservation laws with viscosity to solutions having shocks of hyperbolic conservation laws without viscosity as the viscosity tends to zero. our analysis reveals a rich structure of nonlinear wave interactions due to the presence of shocks and initial layers. These interactions generate four different wave patterns: initial layers, shock layers, diffusion waves and coupling waves. we study the propagation and interactions of the four wave patterns by a detailed pointwise analysis.
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