Area-averaged void fraction images of convective boiling in a branching channel heat sink were acquired with a high speed high resolution camera at a rate of 1,000 frames per second for one second. Data sets are limited by the buffer size of the camera. Test conditions include a flow rate of 30 g/min, 30 W of energy added, and a subcooling of approximately 11°C. Time-varying area-based void fraction data were estimated using an image processing algorithm designed to minimize noise. Conditions for upstream bubble growth are reported as are liquid momentum, evaporation momentum, and surface tension forces for two extreme mass fluxes through the channels. Mass fluxes vary for each branching level as well as with the amount of vapor present in the heat sink. The heat sink is 38.1 mm in diameter with a radial branching flow pattern. The ratio of daughter-to-mother branching lengths is equal to 1.4, which is in contrast to a previous investigation in which the length scale ratio was 0.70.
The performance of two-phase flow through fractal-like heat sinks, subject to both geometrical and flow constraints was assessed. Constraints are crucial in order to satisfy physical requirements of a design. A one-dimensional model of two-phase flow through fractal-like branching microchannels was used to estimate pressure drop, wall temperature and critical heat flux. Water is employed as the working fluid. The exit pressure is varied between 6 kPa and 101.3 kPa (absolute) in order to achieve two-phase flow at temperatures lower than the maximum wall temperature constraint of 70°C. Preliminary results show that the benefit to cost ratio of two-phase flow is on the same order of magnitude as single-phase flow, both with a 70°C wall temperature constraint. Alternatively, a critical heat flux model is used to constrain the flow rate in order for the imposed heat flux to be 50% of the critical heat flux.
This paper reports on a new low-noise blower rotor technology developed by Intel Corporation (patents pending). The new approach replaces the traditional centrifugal blower rotor with a block of continuous porous media. The porous media can be as simple as a low-cost, block of open-cell foam and has no blades or macroscale structure. As the porous media rotor rotates, viscous and inertial forces from the volumetric resistance of the porous media cause the air within the rotor to rotate with it, creating centrifugal forces that overwhelm the flow resistance in the radial direction and create a flow pattern similar to that achieved in a traditional blower. However, because of the lack of distinct blades, the porous-media generates nearly zero aerodynamic tonal noise and significantly reduced broadband noise. This allows the rotor to be operated at significantly higher RPM and reduced clearances relative to the traditional rotor design for further improved performance. This paper will discuss numerical modeling and experimental development of the new blower type. An iso-flow comparison of porous-media and traditional rotors with the same motor and housing demonstrate a 5 dBA reduction in broadband noise and a factor of two reduction in tonality while maintaining comparable overall efficiency. Impact of porosity and different rotor support structures are also discussed.
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