Thermal Simulation Validates Motor Design and Reduces Heatsink Weight
AnJen Solutions recently used Flomerics' FloTHERM computational fluid dynamics (CFD) software to assist MagneMotion, Inc. in their design of a vertical lift elevator made of linear synchronous motors (LSM). AnJen Solutions performed a weight versus thermal performance analysis of the LSM rail heatsink. "FloTHERM provided a detailed understanding of the conductive heat transfer between the heatsink and the LSM rail support structure and convective heat transfer to the surrounding environment," said Michael Rigby of AnJen Solutions. "The simulation demonstrated that reducing the number of fins and changing the fin spacing and thickness would reduce the weight of the heatsink by 1/3 while providing the same thermal performance as the initial design."
The rail thermal load and vertical orientation required a more detailed thermal simulation than is typically done on horizontally oriented LSM rails that make up material transport systems. The vertical orientation results in non-constant heat transfer coefficient and rising ambient air temperature. The temperature of the LSM rail encapsulation material is the limiting factor.
The advantage of CFD is its ability to model the airflow around the LSM which makes it possible to predict convection accurately. Flomerics' FloTHERM software is specially designed for the challenges of modeling thermal management of electronic and electrical systems. "FloTHERM offers a wide range of features such as an automatic optimizer and compact models that make it possible to improve cooling performance and reduce engineering time," Rigby said. "These and other capabilities of the software made it possible to optimize the design of the heatsink which was important because the overall weight of the LSM was a critical concern to MagneMotion's customer."
FloTHERM solved the complete thermal problem including conduction from the motor through the mechanical structure and the heat sink and convection from the mechanical structure and heat sink to the air. FloTHERM solved the buoyancy equations to determine the airflow caused by the heat loading. Rigby evaluated 11 different design scenarios by varying the heat sink fin count and thickness in the model. A fin count of 15 and fin thickness of 3 mm provided the lowest weight while still meeting the encapsulation temperature limits. The weight of 39 pounds for the optimal heat sink configuration provides a weight savings of more than 1/3 compared to the baseline configuration.
"FloTHERM provided a detailed understanding of the convective heat transfer from the LSM heatsinks and structural supports and of the conductive heat transfer within the structure," Rigby concluded. "The CFD simulation saved engineering time and reduced time to market by enabling us to verify the thermal design of the entire LSM without having to build a prototype. Simulation also enabled a substantial reduction in weight and hence material cost of the heat sink."
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