Annex D) Computational Fluid Dynamics and Innovative Heatsink Tech

CFD and Waterblock Flow Optimizations : An interesting read on Advanced Power Electronics Thermal Design here, especially the part about optimizing the design of a water block for better flow dispersal using CFD software. Here's an excerpt; NREL report: "Figure 1 shows the velocity distribution in the current design. A nominal design coolant flow rate of 10 l/min is used to generate the resulting flow field. CFD analysis shows how the incoming flow impinges on the diamond boss and causes the flow to split into two major streams. These narrow streams then impinge directly on the pin fins in the first few rows. Because of the high impingement velocity at the diamond boss, the flow attaches to the sidewalls of the boss and a substantial portion of the flow is diverted around the interior pin fins. The CFD analysis predicts two large re-circulation regions at the entry and a large wake downstream of the boss. Consequently, the analysis shows that a major portion of the coolant bypasses most of the interior fins and flows along the two straight unobstructed channels along the sidewalls, thereby decreasing the heat exchanger effectiveness and increasing its thermal resistance in the inverter cooling design. This inevitably causes IGBT temperatures to increase." "Figure 2 illustrates that the flow around the boss now remains attached and smoothly distributes to the fins downstream. The reduction in the flow channel width at entry allows the flow to diffuse out more gradually. The presence of partial fins along the sidewalls as projections into the channel prevents the flow from bypassing the fins. A more uniform distribution of the flow velocity is apparent in this figure. Closer examination of the flow field reveals that the regions of flow separation behind the mounting bosses and fins are reduced substantially from the original design. The flow maintains a high velocity adjacent to the sidewalls of the pin. Both these features will keep the flow channel swept of potential debris and minimize the tendency for fouling."

Furukawa Hexagonal Crimped Fin Heatsink Prototype : This prototype heatsink comes to Frostytech by Furukawa Electric Co., Ltd., and looks to be the makings of a next generation socket 775 cooler. Called the 'Hexagonal Crimped Fin' heatsink, it has a thermal resistance of just 0.246 K/W. Whether this signals the retirement of AVC's stock bifurcated fin heatsink model currently being used of the Pentium 4 is anyone's guess. The authors of a report on this heatsink document several prototypes which failed to out-perform the standard socket 775 Intel bifurcated fin in their attempt to advance crimped fin heatsinks. The hexagon-shapped copper core was selected as it was the only shape able to meet the mechanical needs of the crimping process for all 132 fins (each 0.3mm thick, in pairs), and final circular shape requirements. The bend in each set of fins 2/3's of the way out is meant to maintain geometry between each the tips.

Corona driven air propulsion for cooling of electronics : This research paper explores the viability of Corona Driven Air Propulsion for electronics cooling. It's the first I've heard of such an application, although the method seems fairly similar to some piezoelectric methods in a couple respects. Read the 4-page PDF on Corona Air Propulsion here. Washington.edu: "The possibility of building a high voltage electrostatic air pump for cooling of microelectronics is investigated. Heat sink fins are packed more closely to increase the heat exchange surface area, resulting in narrower channels between the fins. Air viscosity in narrow channels reduces the cooling efficiency of the heat sinks. Electrostatic air propulsion methods may improve airflow patterns in narrow channels. Several prototypes of the electrostatic air pump were built. Corona onset voltage was measured, and the current-voltage relationship showed a positive exponential relationship. The performance of the corona pump displayed a nearly linear voltage-air velocity relationship, a logarithmic decrease in air gap impedance between corona and collector electrodes, and a departure from classic air velocity profiles."

That's all for now, Frostytech will update this article in the future as more curious technology surfaces from the archives. Feedback is welcome, as are tips about new cooling technologies.