本研究利用質點軌跡流場觀察法(PTFV)與質點影像速度儀(PIV)
之技術，診測風扇出口流場在軸向與徑向平面的特性，然後以市面上
販售的CPU 散熱模組為藍本，藉由實驗方法探討散熱模組鰭片內之
流場。接著發展輕薄型之整流裝置，置於風扇與鰭片之間，以質點軌
跡流場觀察法與質點影像速度儀技術進行診測，得到良好的流場以增
強CPU 散熱模組的散熱效果。最後再進行未改裝與已改良後CPU 散
熱模組的性能測試，驗證所發展出來的整流器之有效性。質點軌跡流
場觀察法以比重1.03 塑膠顆粒做為媒介，配合雷射光頁與高速攝影
機得到流場觀測照片。質點影像速度儀是針對流場作量化的分析，得
到速度場及流線分佈。在不同導流片角度下，使用定溫型的熱線風速
儀，量測風扇入口的體積流率。利用熱電偶量測散熱模組之發熱體與
環境的溫度。實驗顯示，在風扇葉穀下方產生迴流，且風扇出口流場
受水槽尺寸的影響，造成流場結構呈現方形。經由導流段中增置經適
當設計的導流片整流後，可有效抑制將鰭片內的迴流現象，達到增加
有效散熱面積的效果。使用導流段高度3 mm 及導流片角度-15o 的整
流器，在80W 的加熱率時，能將原本CPU 模擬器的溫度與環溫之差
值降低約11%。顯現經流場調整後，散熱增強的效果頗為明顯。

This study uses the particle tracking flow visualization method
(PTFV) and the particle image velocimeter (PIV) to obtain the dynamic
flow patterns and quantitative velocity distributions of the exit flows of
axial fan and the flow structures between neighboring fins of the CPU
cooler with an axial fan installed at the top of the heat sink. Both the flow
fields at the exit of the fan and between neighboring fins of the CPU heat
sink are characterized by a pair of counter-rotating vortices. The existence
of the vortex pair makes the flow recirculate and retard in the gap
between the fins so that the heat transfer rate from the fin surfaces to the
flow is phenomenologically deteriorated. In order to reduce the negative
effect of the flow patterns on the heat transfer rate, various means of flow
conditioners are developed, e.g., the elongated plenum chamber, the cone
at exit, and the guide vanes. The PTFV and PIV are again employed to
diagnose the flow patterns after application of the flow conditioners. It is
found that the methods of adding a plenum chamber and installing a
cone-shaped extension section behind the fan hub are not substantially
effective. The recirculation bubble would not disappear in a limited
length of the plenum chamber. The recirculating flow does disappear in
the flow conditioner with a long cone attached behind the fan hub.
However, the flow velocity around the cone becomes drastically low so
that the heat transfer performance would be down-graded. The guide-van
flow conditioner is the only way that can achieve the goal of straightening
the flow and cause insignificant head loss. A specially designed van
arrangement pattern is successfully developed. The recirculation bubble
between the neighboring fins almost diminishes and the pressure drop
across the conditioner is optimized. The standard test methods applied to
both of the natural and the flow-conditioned cooling modules show that
the currently developed flow conditioner can effectively reduce the
temperature of the CPU simulator. At its optimized cases, it is possible to
use a guide-van flow conditioner of only 3 mm height to decrease the
temperature of the CPU simulator by around 11% when compared with
its natural situation.

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