Temperature Estimating and Measuring Methods
The following methods can be used to estimate air cooling requirements and calculate junction temperature based on
Airflow Cooling Measurement Method
The relationship between air temperature and junction temperature is described in the following thermal equation:
Tj = Ta + [Pd (θjc + θcs + θsa)]
Note: Testing is done with the
Determination of the ambient air temperature (Ta) and the
Note that the airflow velocity can be measured using a velocity meter. Alternatively it may be determined by knowing the performance of the fan that is supplying the airflow. Calculating the airflow velocity is difficult. It is subject to the interpretation of the term
Note: The Airflow Cooling Estimate method is an estimate. Use it solely when an approximate value suffices. Accuracy can only be assured using the Case Temperature measuring method or the Heatsink Temperature measuring method. Apply these methods to insure a reliable performance.
Heatsink-to-Air Thermal Resistance
Air Velocity |
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(ft/min) [1] | 150 | 200 | 300 | 400 | 500 | 650 | 800 | 1000 |
θSA (°C/W) [2] | 1.21 | 1.05 | 0.91 | 0.84 | 0.78 | 0.72 | 0.67 | 0.64 |
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1.Ducted airflow through the heatsinks.
2.Airflow direction parallel to the shorter axis of the
Air Velocity Specifications
These specifications are recommended for a typical configuration:
Airflow Topside
150 LFM @ 30 °C up to 2,000 feet, altitude, maximum
300 LFM @ 40 °C up to 10,000 feet, altitude, maximum Airflow Bottomside
100 LFM @ 30 °C up to 2,000 feet, altitude, maximum
150 LFM @ 40 °C up to 10,000 feet, altitude, maximum
20 | Sun Microsystems, Inc | July 1999 |
