Simulation Helps Hybricon Design 8U Chassis That Dissipates 30% More Power

Thermal simulation played a key role in helping Hybricon design an 8U chassis that dissipates 30% more power than competitive offerings. With 6U high vertical cards, 8U chassis design is challenging because only 1 U is available above and below the card cage for airflow. The typical approach utilizes 1 U tall blower boxes located directly over the card cages. In developing the new chassis, Hybricon engineers used Flotherm thermal simulation software from Flomerics to simulate pressure and velocity distribution through the chassis and make design changes to provide even flow distribution to the slots. They also evaluated different fans and air filters to provide further performance improvements. The result is that the worst slot on the Hybricon 8U chassis cools 30% more power than the leading competitive design with a low capacity fan and 85% more power with a high-capacity fan.

“The definition of circuit card heights and depths and how they interface with the backplane is one of the key reasons for the success of industry-standard VME, VME64X and CPCI systems,” said Bob Sullivan, Chief Technology Officer for Hybricon. “But the industry standards do not effectively address cooling and thermal management issues, so thermal management problems often lurk in the background until the design hits the engineering lab, or even worse, the customer site. But the desire for smaller chasses with increasing heat dissipations can be accomplished with careful attention to flow path management, understanding areas of flow restriction, circuit card selection and air mover selection. We use a variety of tools to address these challenges, including hand calculations and flow network modeling tools, but the most powerful by far is Flotherm, our thermal simulation tool of choice. Flotherm provides detailed graphical information on pressures, temperatures and airflows throughout our design, providing detailed insights on how the design can be improved. A key advantage of the software package is that it is designed for use by mechanical design engineers, which allows us to quickly optimize solutions.”

“In the design of the 8U chassis, we met demanding packaging volume goals by controlling and managing airflow paths within the chassis, Sullivan continued. “Knowing the typical chassis environment and how systems-level chassis decisions are made, we designed the 8U chassis to meet the thermal needs of most applications. This was accomplished through careful air path and fan selection management to ensure that the correct amounts of cool air are provided to the critical electronics within the chassis, following a known and controlled airflow path, with even flow distributions. When we finished optimizing the design from a thermal standpoint, our Flotherm analysis showed that the air velocity through the chassis was relatively uniform with only the inlet area and the area of transition to the volume behind the card cage showing lower air velocity. The flow rates for each slot, as measured in Flotherm were also quite uniform, ranging from 5.2 CFM to 6.4 CFM with the low capacity fan and 7.4 CFM to 9.5 CFM with the high capacity fan. The relatively low slot to slot variation is the key to the excellent thermal performance of the new chassis.”