Abstract
Air flow and heat removal characteristics for fan/heat sink designs used to cool Pentium class processors were analyzed. Five designs were tested for fan speed, differential and static nozzle pressure, static fan pressure, fan input current and voltage, wet and dry bulb temperatures, nozzle temperature, barometric pressure and the fan outlet area. These measurements were used to determine the best performing fan/heat sink design. The results of these fan performance tests showed fans that are similar in physical characteristics vary greatly in their performance. At a static pressure of 0.2 in. wg (49.8 Pa) the air flow rate ranged from 1.81 to 5.88 CFM (0.85 to 2.78 dM3/S) with the fan alone and ranged from 0.93 to 5.58 CFM (0.44 to 2.63 dM3/S) with the heat sink attached. These results also showed that all but one of the fan/heat sink designs had restricted air flow for the fans when the heat sink was in place. Tests with a Pentium [ ] processor and fan/heat sink designs revealed the effects of using different fan/heat sink designs on the top and bottom surface temperatures of the processor and the heat flux at the top surface of the processor. At a CPU speed of 200 MHz, the top and bottom surface temperatures were 120.6'F (49.2'C) and 138.9'F (59.3'C) for one of the poorest performing fan/heat sink designs and were 102. 1 'F (3 8.9'C) and 123.3'F (50.7'C) respectively, for the best design. Other testing with the processor determined that an increased air flow rate over the processor will enhance heat transfer. This was shown by measuring the surface temperatures and heat flux for the CPU with two different fans attached to the same heat sink at a speed of 200 MHz. The temperature difference between the two fans ranged between 1.5 to 7.6'F (0.83 to 4.2'C) for both surfaces. An increased air flow rate can be obtained by using a better fan and heat sink design or by changing the fan and heat sink design from a surface mounted design to an elevated design.
Baltrip, Kedra G (1997). The Effect of Fan and Heat Sink Design on Heat Removal from Microprocessor Chips. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1997 -THESIS -B36.