Search

Computations have been conducted on curved, three-dimensional discrete-hole film cooling geometries that included the mainflow, injection hole, and supply plenum regions. Both convex and concave film cooling geometries were studied. The effects of several film cooling parameters have been investigated, including the effects of blowing ratio, injection angle, hole length, hole spacing, and hole staggering. The blowing ratio was varied from 0.5 to 1.5, the injection angle from 35 to 65 deg, the hole length from 1.75D to 6.0D, and the hole spacing from 2D to 3D. The staggered-hole arrangement considered included two rows. The computations were performed by solving the fully elliptic, three-dimensional Navier-Stokes equations over a body-fitted grid. Turbulence closure was achieved using a modified k-(epsilon) model in which algebraic relations were used for the turbulent viscosity and the turbulent Prandtl number. The results presented and discussed include plots of adiabatic effectiveness as well as plots of velocity contours and velocity vectors in cross-stream planes. The present study reveals that the blowing ratio, hole spacing, and hole staggering are among the most significant film cooling parameters. Furthermore: (1) The optimum blowing ratios for curved surfaces are higher than those for fiat surfaces, (2) a reduction of hole spacing from 3D to 2D resulted in a very significant increase in adiabatic effectiveness, especially on the concave surface, (3) the increase in cooling effectiveness with decreasing hole spacing was found to be due to not only the increased coolant mass per unit area, but also the smaller jet penetration and the weaker counterrotating vortices, (4)for all practical purposes, the hole length was found to be a much less significant film cooling parameter.

A numerical study has been conducted to investigate the effects of surface curvature on cooling effectiveness using three-dimensional film cooling geometries that included the mainflow, injection hole, and supply plenum regions. Three surfaces were considered in this study, namely, convex, concave, and flat surfaces. The fully elliptic, three-dimensional Navier-Stokes equations were solved over a body-fitted grid. The effects of streamline curvature were taken into account by using algebraic relations for the turbulent viscosity and the turbulent Prandtl number in a modified k-(epsilon) turbulence model. Computations were performed for blowing ratios of 0.5, 1.0, and 1.5 at a density ratio of 2.0. The computed and experimental cooling effectiveness results were compared. For the most part, the cooling effectiveness was predicted quite well. A comparison of the cooling performances over the three surfaces reveals that the effect of streamline curvature on cooling effectiveness is very significant. For the low blowing ratios considered, the convex surface resulted in a higher cooling effectiveness than both the fiat and concave surfaces. The flow structures over the three surfaces also exhibited important differences. On the concave surface, the flow involved a stronger vorticity and greater mixing of the coolant jet with the mainstream gases. On the convex surface, the counterrotating vortices were suppressed and the coolant jet pressed to the surface by a strong cross-stream pressure gradient.

Forced flow of air over extended surfaces offers a simple, reliable, and effective heat removal mechanism and is often employed in electronic equipments. The IBM 4381 heat sink, used in production IBM computers, utilizes this cooling technique. This heat sink Consists of a ceramic substrate on which fins made of an aluminum-copper alloy are arranged in a regular array. Cooling air enters the fin array from a nozzle. Extensive experiments have been carried out to characterize the performance of this heat sink at the Advanced Thermal Engineering Laboratory at IBM Endicott. This paper presents computational analysis of the three-dimensional flow and heat transfer in this device for two different airflow rates through the nozzle. The heat dissipated by the electronic components is conducted into the fins through the ceramic base. In the present study the ceramic base is assumed to be subjected to a uniform heat flux at the bottom. The computational method incorporates a special block-correction procedure to enable iterative solution of conjugate heat transfer in the presence of large differences in thermal conductivities of the air and the fin material. The results of computations reproduce the flow pattern in the fin array that is observed experimentally. The part of the ceramic base directly below the nozzle is well cooled with the temperatures gradually increasing from the center towards the corner. The predicted pressure drop and most of the local temperatures at the base and the tip of the fins agree well with the experimental observations. This study illustrates the utility of computational flow analysis in the analysis and design of electronic cooling techniques.

The modified-exponential spatial differencing scheme of radiative transfer applies the exponential scheme in nonscattering media, while in scattering media, the scheme uses grid-independent solution with fewer grid points. Use of the improved source-term linearization and traditional iteration approaches yield similar solutions, although the improved iteration treatment tends to the convectional approach in nonscattering media.

The laminar natural convection in partitioned cubic enclosures is analyzed. Results are presented for a range of Rayleigh numbers and opening heights. It was observed that the Rayleigh number and opening height affected the fluid flow and heat transfer in the enclosure. Heat transfer rates increased with increasing Rayleigh numbers and opening heights. Average Nusselt numbers for two-dimensional and three-dimensional partitioned enclosures were also analyzed.

A study of the radiative heat transfer in three irregular enclosures with absorbing, emitting and anisotropic scattering media provides solutions by Monte Carlo method. It covers the scattering phase functions and scattering albedos for purely absorbing and purely scattering cases. The outcome will be significant for verifying new solution processes for complex geometries' radiation heat transfers.