Software helps deal with growing heat problem

The Redback SE1200 platform contains a total of 12 line cards, whose power dissipation is substantially higher than the previous-generation product.

Flomerics' Flotherm software helped Redback Networks overcome the cooling challenges involved in creating the first million-subscriber triple-play platform.

"The power dissipation of the line cards in the new platform had to be increased by 2X relative to the previous generation to obtain the planned improvement in performance and functionality", said Wendy Lu, Mechanical Engineer for Redback Networks.

"By focusing on reducing the chassis static pressure via geometry changes and using a higher performing fan, we were able to double the airflow in the chassis".

Fifteen of the world's top 20 telephone carriers use Redback's SmartEdge router platform to deliver a mix of broadband, phone and TV services to more than 50 million subscribers.

Redback Networks is creating the first million-subscriber platform for triple-play services such as high-definition television (HDTV), high-density video on demand (HD VoD) and broadband mobility.

The Redback SE1200 platform contains a total of 12 line cards, whose power dissipation is substantially higher than the previous-generation product.

In order to maintain the same system thermal performance, more airflow is required to remove additional heat from new line cards.

Starting with a system level model of the chassis, Lu first tried improving performance by substituting a more powerful fan.

This increased airflow by 50%, but it was not good enough.

Next, Lu looked at enlarging the plenum geometry to reduce system static pressure.

However, she also needed to maximise the number of chassis per rack.

She used Flotherm's Command Center to quickly evaluate the optimised plenum geometry to obtain the required level of airflow.

Then, using Flotherm detailed board model, Lu ran additional simulations in the system level model to ensure critical components can be cooled to within the manufacturer's specification.

Lu also performed a number of simulations to evaluate different failure modes.

The simulation results revealed that a fan failure caused airflow recirculation, which reduced system airflow and overheated the affected region.

Lu added a louver assembly to each fan, which automatically closes the fan opening if a fan fails.

This effectively eliminated recirculation.

Lu then commissioned a foamcore model of the new plenum so that physical tests could be performed quickly.

The lab measurements closely matched the simulation results so no thermal design changes were required during the prototype phase.

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