Selecting a Fan for Your Thermal Management System (part 1 of 2)

Designing a forced convection system for a chassis or cabinet is a complicated task which must be done correctly to ensure the performance and reliability of the enclosed electronics. There are many thermal, mechanical, and electrical effects to consider when selecting a fan.

First the type of fan needs to be selected, based on chassis design and allowable space. The two types are:

Vane-Axial- Air flow is parallel to the fans Axis, high flow rate, and low pressure (figure 1)

Vane Axial FanBlower- Air flow is perpendicular to fan axis, low flow rate, and high pressure (figure 2)

Blower air mover

To select the appropriate fan we need to estimate the necessary airflow needed for a system. For low power, uniform heat loads we can use a simple steady state analysis to balance airflow and temperature rise. The power dissipation of the chassis and desired temperature rise are used in the following equation to obtain a target flow rate.

equations for air movers and fans in chassis

For high heat loads, with concentrated heat sources you must design to the worst case component. Spot cooling may be accomplished with internal fans, heatsinks, ducting etc.

On Wednesday we’ll have the second part of this article, covering the total system impendance curve and more on calculated flow rates.  Click here to right to part 2.


common fan laws

Common Fan Laws for Electronic Enclosures

1. Fan Cooled Enclosure Analysis Using a First Order Method, Ellison, Gordon, N., Electronics Cooling, Vol. 1, No. 2, October 1995, pp. 16-19.

2. Practical Guide to Fan Engineering, Daly, Woods, Woods of Colchester, Ltd, 1992

3. All you need to know about fans, Mike Turner, Electronics Cooling, Vol.1 May 1996

4. Comair Rotron, Establishing Cooling Requirements: Air Flow vs. Pressure,, March 12, 2007

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