Thermal Simulation Helps Overcome Challenge of 14U Chassis with 1700 Watts
december 2007
amphenol total connection solutions (tcs) used flomerics’ flotherm software to overcome the thermal management challenges of a 14 rack unit (u) chassis dissipating 1700 watts. amphenol engineer chris heard simulated the product, which includes a total of fourteen 100-watt and two 150-watt printed circuit boards (pcbs). “this project demonstrates how thermal simulation can be used in the early stages of the design process to minimize expensive late-stage changes and reduce time to market,” heard said.
a network equipment supplier conceived of a new data communications product capable of providing dramatic improvements in performance. but these improvements came at the price of exceptionally high power dissipation of 1700 watts. this provided a tough thermal challenge in the telecom central office where equipment must fit within tight space constraints and demonstrate the ability to operate even after fan failures.
the network equipment supplier asked amphenol tcs, the backplane supplier, to perform thermal simulation in the concept phase in order to verify the viability of the new chassis concept. amphenol began the project by analyzing the airflow through the chassis with an internally developed hydraulic resistance simulation tool called the chassis thermal analyzer. this tool provides very fast simulation results because it does not take the detailed geometry of the chassis into account. heard evaluated a number of different designs and settled on one that seemed to work best.
the hydraulic resistance tool told heard that it should be possible to push enough air through chassis but did not explain how hot the air would get or if it would flow into the right places. to answer these questions, heard used flotherm computational fluid dynamics (cfd) software from flomerics.
“flotherm goes one major step further than our internal code by modeling the entire geometry of the chassis,” heard said. “i can specify where the power is dissipated and the simulation tracks the flow of air and transfer of heat throughout the chassis. we have used flotherm for 16 years and have developed a high degree of confidence in its accuracy. most of our larger customers also use the software so we can easily exchange models with them.”
heard modeled the geometry of the enclosure in flotherm. he used flotherm’s pcb smartpart instead of modeling the full geometry of the pcbs. the advantage of using the pcb smartpart instead of defining the board geometrically is that the smartpart can be defined much faster by filling in the blanks in the form-based menu system. the use of smartparts also reduces the complexity of the model and hence the time required to perform the simulation.
“the simulation demonstrated that this power new data communications product could be successfully cooled in a 14u chassis while meeting nebs requirements,” heard said. “the network equipment manufacturer proceeded with the design with confidence that thermal management would not delay the project. when more design information became available, the manufacturer simulated the design again, made minor changes and successfully brought the product to market without any thermal issues.”
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