An experimental investigation of heat transfer by natural convection from a smooth, isothermal cubic cavity with a variety of side-facing apertures is described in this paper. The study was motivated by the desire to predict the convective loss from large solar thermal-electric receivers and to understand the mechanisms which control this loss. Hence, emphasis is placed on the large Rayleigh number, Ra, regime with large ratios of the cavity wall temperature Tw to the ambient temperature T∞. A cryogenic wind tunnel with test section temperatures which are varied between 80 K and 310 K is used to facilitate deduction of the influences of the relevant parameters and to obtain large temperature ratios without masking the results by radiative heat transfer. A 0.4-m cubic cavity, which is mounted in the side wall of this tunnel, is used. The area of the aperture Aa and its location are key variables in this study. The data which are presented cover the ranges: 1 < Tw/T∞ < 3, L2/18 ≤ Aa ≤ L2, and 3 × 107 < Ra < 3 × 1010.
This paper presents a study of the fluid dynamics and heat transfer phenomena occurring during the impingement of a picoliter size liquid solder droplet upon a multilayer, composite substrate. The theoretical model, based on the Lagrangian formulation, is solved numerically with the finite element method. A deforming mesh is utilized to accurately simulate the large deformations, as well as the domain nonuniformities characteristic of the spreading process. The occurrences of droplet recoiling and mass accumulation around the deposit periphery are features of the numerical simulations and yield a nonmonotonic dependence of the maximum radius on time. The results also document the transient temperature fields developing in both the solder droplet and the substrate during the impingement process. Convection effects on the temperature field development in a deforming droplet are found to be important for the entire history of spreading. The work is directly applicable to the miniature solder droplet dispension technology for the mounting of microscopic electronic components on various substrates under development at MicroFab Inc. The results of the numerical simulations are used to explain the shape of solidified microscopic solder bumps.
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