摘要:

This article describes a numerical investigation of micropore formation in solidifying molten metal droplets impinging on a colder substrate. The velocity field inside the spreading liquid droplet is computed as a solution of the incompressible Navier-Stokes equations, and a volume-of-fluid function is defined in order to track the location of the free surface. A multidirectional solidification model is implemented to simulate the formation of possible pores, cavities, and/or troughs. This tracking algorithm allows for complex interface morphology representation as well as interface merging simulation. In the test case considered (high-velocity impact of a single droplet), simulations predict the formation of an annular trough on the surface of the solidified splat. This feature may be a precursor of pore or cavity formation in multiple-droplet cases.

ISSN:1040-7782    

DOI:10.1080/10407789608913825

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A transient three-dimensional analysis was performed for passive thermal control of a plastic quad flat package by incorporating an organic phase change material (PCM) under the printed wiring board. Governing conservation equations for mass, momentum, and energy were solved by an implicit finite volume numerical technique. The effects of phase change were modeled by a single-domain enthalpy-porosity technique. To study the effects of thermal conductivity of the board, a total of six cases were considered with two different board materials. It was found that passive cooling with PCM can arrest the temperature rise for substantial time, for the power levels considered. A higher board thermal conductivity resulted in a reduction in temperature levels. The melt region for a lower thermal conductivity of the board was found to be localized near the package footprint, while for a higher board conductivity, the melt region extends along the board.

ISSN:1040-7782    

DOI:10.1080/10407789608913826

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The diffusion bonding procedure between two stages of a nickel alloy drum rotor surrounded by a double-wrapped heating coil is modeled by computing the time-dependent temperature field and stresses. The power deposition in the workpiece is modeled by numerically solving the low-frequency Maxwell equations in the enclosure. Nonlinearities due to temperature dependent electrical, thermal, and stress-related properties are handled by iterating between the solvers for the magnetic potential, temperature, and stress. Parametric studies are performed to investigate the influence of coil placement and pressure load on the temperature and stresses near the bond joint.

ISSN:1040-7782    

DOI:10.1080/10407789608913827

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The flow field of a transverse jet in a supersonic airstream subjected to shock wave-turbulent boundary layer interactions is simulated numerically by adaptive mixed explicit-implicit generalized-Galerkin finite element methods. In this scheme, convection and diffusion implicitness parameters are introduced to resolve shock wave discontinuities and widely disparate time and length scales of turbulence and finite rate chemistry. These parameters are flow field dependent, calculated from local Mach, Reynolds, and Damkohler numbers for each element. Effects of turbulence are taken into account with a two-equation (k-ϵ) model with a compressibility correction. Various cases of mixing, slot widths, and total pressure ratios with and without chemical reactions are examined. Favorable comparisons with experimental measurements are demonstrated.

ISSN:1040-7782    

DOI:10.1080/10407789608913828

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Combined natural convection and radiation heat transfer in a vertical air cavity with a hexagonal honeycomb core of negligible thickness are investigated numerically. The numerical methodology is based on an algebraic coordinate transformation and finite volume technique. Temperature of the honeycomb core wall is determined such that radiation, convection, and conduction energy balances on the core wall are satisfied. The computations were performed forRa = 103−105, for an aspect ratio ofH/L = I, forPr = 0.7, and for a wide range of emissivities. Heat transfer rates by both convection and radiation are presented as a function of emissivity, and the effect of radiation on the natural convection is discussed. The results showed natural convection is affected by radiation although the layer is filled with a transparent gas. This effect is accentuated in the case of a very thin wall.

ISSN:1040-7782    

DOI:10.1080/10407789608913829

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The velocity field and heat transfer in rows of rectangular impinging jets have been analyzed from the numerical solution of unsteady Navier-Stokes and energy equations. Jets emanating axially and radially from rectangular slot nozzles (feed tubes) have been considered. For the radial jets, the jet exit angle has also been varied. Steady flows have been obtained for Reynolds numbers smaller than a critical value above which periodic flows appear. At a higher Reynolds number than the critical value, the flow becomes unsteady and nonperiodic. For the laminar axial jets, an optimum relative nozzle area for maximum heat transfer, as experimentally observed for turbulent jets, is also obtained. For the radial jets, heat transfer monotonically increases with relative nozzle area. For the densely spaced jets, i.e.,for a large relative nozzle area, average heat transfer for the radial jets can be larger than that for the axial jets. Heat transfer can also be substantially increased by vectoring the radial jets toward the impingement surface. Densely packed and vectored radial jets can give 20%-30% more heat transfer than the axial jets, for the same mass flow ate.

ISSN:1040-7782    

DOI:10.1080/10407789608913830

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor