This paper describes an experimental study of free convection in an enclosed rectangular cavity, the end walls of which are maintained at uniform but different temperatures. The experiments are carried out for a variety of Rayleigh numbers, R = αgΔTh4/κνl, and aspect ratios, L = l/h, for fluids with Prandtl number σ ≥ 10. For R ∼ O(103) it is shown that the basic structure of the flow field is a single two-dimensional cell for 0·25 ≤ L ≤ 9. When R > O(104) the boundary layers on the vertical walls control the flow field, but the basic overall structure remains unicellular. At greater values of R secondary vortices appear for all L ≥ 0·5. As R increases the intensity and then the number of these vortices increases. Measurements of the end-wall boundary-layer profiles at different values of R and L confirm Gill's boundary-layer analysis. The effects of variations of viscosity with temperature are discussed in the context of the observed boundary-layer profiles.Core shear profiles and mass flux measurements are also reported. For L = 1 the observed shear profiles are in good agreement with numerical solutions of the Boussinesq equations. However, when L > 1 the observations suggest that the horizontal boundary layers have a significant effect on the core flow field. The stream function is demonstrated to be L-dependent in the boundary-layer regime, where variations due to R are second order. Similarities between the results of the present work and earlier observations by Elder and by Seki, Fukusaka & Inaba for tall slender cavities (L [Lt ] 1) are discussed.
Quantitative velocity measurements of unsteady convection in a Bénard cell suddenly cooled from above to a supercritical Rayleigh number are reported. The results are obtained by a novel application of laser speckle photography adapted for the study of fluid dynamics. This technique allows two-dimensional full-field velocity information to be obtained solely from a selected plane within the volume of moving liquid at any given instant in time. The convective rolls are found to be regular and oriented parallel to the short side of the cell. The number of rolls within the cell is approximately twice as great as the number reported for steady conditions. The maximum vertical velocity distribution is observed to be a sinusoidal function of the horizontal distance with a detectable third-harmonic component.
Low cycle fatigue studies of solder joints designed and fabricated to represent generic interconnection structures typical of what might be used in packaging microelectronics have been carried out to assist in the development of a better understanding of the fundamental mechanical properties that determine the reliability of such structures. These studies involve micro scale joints (micro-joints) of both eutectic and 95/5 Pb/Sn solders fabricated by several different processes. In addition to a discussion of the results of recent tests reflecting specified loss-of-strength failure criteria and extensive post-test failure mode analysis of, primarily, 95/5 Pb/Sn micro-joints, descriptions of (1) the design and fabrication of the custom shear test vehicles and (2) the high-resolution electro-mechanical loading system used to apply cyclic loadings under isothermal conditions will be presented. This computer controlled system provides for the application of fully or partially reversed shear strains (with or without dwells) to either prototypes or custom test vehicles, and can be operated to maintain either total or plastic strain control during cycling.
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