By Dr. Samir El-Khabiry, Hamilton Sundstrand, Rockford, IL

Thermal control is important for the safe and reliable operation of electronic equipment. However, with increased functionality and the continued miniaturization of electronic systems, increases in the amount of heat generated per unit volume have become an issue. Removing the internally generated heat requires an effective path along which the heat can flow from the components to their surroundings. Cooling techniques such as conduction, natural or forced convection, radiation, and liquid cooling are typically used, depending on the situation. At Hamilton Sundstrand, FLUENT and Icepak have both been used to simulate virtual prototypes of electronic equipment and the cooling mechanisms that could potentially be used to transfer heat. CFD has made it possible to evaluate a number of possible designs before building an actual prototype for testing.

Using FLUENT, the thermal performance of one of the electronic control boxes of an aircraft was recently analyzed. The controller houses the Motor Drive Module (MDM) of the flap/ slat control unit, which is used to extend the flaps of a commercial aircraft during takeoff and landing, and to retract them when they are no longer needed. The module fits inside the wing of the aircraft, and includes a powerful motor, with control circuitry that dissipates a large amount of heat. The module geometry was created using Pro/ ENGINEER ® and imported into GAMBIT for mesh generation. The box is cooled by fandriven forced air, so the characteristic fan curve (for pressure vs. flow rate) was used as an input for the CFD analysis. The simulation results showed velocity and temperature distributions throughout the module, and helped engineers select the appropriate electronic components for the unit. Detailed visualization of the results helped to understand the system behavior and improve it.

Temperature distribution inside the motor drive module

Icepak has also been used for many electronics cooling projects at Hamilton Sundstrand. For example, the air-cooling system of a control unit for an electro-hydraulic drive unit (EHDU) inverter was recently studied. This unit consists of a 65 kW variable speed permanent magnet electric motor integrated with a 35 gallon/ minute hydraulic pump. Using Icepak, engineers were able to easily position and reposition a number of internal components and fans in order to improve the circulation of the cooling air. The improved circulation allowed them to switch to a heat sink one-third as large as the one in the original design. When it became necessary to replace several components on a printed circuit board of the EHDU, Icepak was again used to determine the impact of the change on the thermal conditions inside the enclosure. The analysis showed that the additional heat generated by the new components raised temperatures beyond acceptable levels. Several alternative designs were evaluated using CFD, and an effective cooling mechanism was identified and applied to the actual board.

Experimental data collected from these and other systems have shown good agreement with the simulation results, thus demonstrating the usefulness of CFD for analyzing complicated systems. This kind of analysis has helped improve product performance and safety, and has saved a significant amount of time and money for the company.

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