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Unique engineering concept to extend future of active cooling
Keywords: telecommunications, cooling, fans
Alcatel's summer 2011 launch of new silicone for edge routers is impressive. Their publicity about this new ASIC chip highlights 400 gigabyte per second speed capability quadrupling that of their previous offering. This release represents a 50% power reduction per unit of processing. But quadrupling capacity with a halving of power per unit of processing equals a doubling of the heat rejection requirements. Because chassis dimensions are not changing the chassis Watt density levels double. What does this mean to traditional cooling systems? Everything being equal the doubling their heat rejection requires a doubling of air flow, quadrupling air pressure and an eight fold increase of power needed by the fans. The stress on thermals in the edge and core router markets is severe and need rethinking relative to the system architectures. Last year I spoke briefly about several alternatives thermal engineers are reviewing. Water cooling, rear chassis hardware systems, micro channel, etc. represent non-traditional architecture, different economics and new risk profiles. These are business issues and they and other technical unknowns will impede implementation of these systems so long as reasonable alternatives exist. Verizon, AT&T and others are heavily invested in systems and infrastructure so are telling their router suppliers to design with the existing chassis packaging and accommodate the higher performance requirements in their central offices. Efficiency is the key. How can the new heat rejection rates be accommodated? One possibility comes from a two year effort that evolved alternative, yet common, packagable, centrifugal blower designs. The fans in routers may be upstream or downstream of the electronics being cooled and must have redundant capabilities for 24/7 operation. Because of the monumental increases in flow and flow resistance the traditional axial fan has yielded to a dual axial fan. The dual axial fans are now nearing their limit of effectiveness. The technical limits are fast approaching for this methodology. The rotational speed of these fans has crept up into the 20,000 RPM range and this has affected the acoustics of the devices. There is no space for mufflers and in many cases the noise levels exceed Verizon and AT&T (NEBS) standards and sometimes the OSHA safety levels as well. We believe that a new design is needed and have devised a technology that achieves performance, efficiency and acoustic goals.
Roger Dickinson,
Bergquist Company
Torrington, CT

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