由於半導體技術的進步迅速，近年來電腦中央處理器運算速度已經大大的提升，晶片表面熱通量也就隨之越來越高。於是如何增加散熱效率帶走更多的熱量，使得系統更穩定也就成為很重要的課題。尤其空間小、散熱模組的阻抗大的筆記型電腦的散熱條件更是嚴苛，所以能產生較大風壓的離心風扇就常常成為首要考慮。
離心風扇除了葉片角度影響性能之外，渦殼的設計的好壞也對於性能有直接的影響。而渦殼舌尖部分流場特性非常不穩定，壓力的變化也相當劇烈。本論文以實驗的方式，研究渦殼舌尖對於整體性能及噪音的影響。在不改變風扇基本尺寸的前提之下，改變葉輪與舌尖的間隙(t)以及舌尖半徑(r)，量測有著不同舌尖外形渦殼的離心風扇性能曲線以及噪音。
結果顯示，當t值(或r值)增加時最大流量會隨著增加，但是會有一極限值。最大壓力則是先稍微下降然後上升，變動幅度不像最大流量明顯。而噪音值對於t值(或r值)的大小的反應比最大流量和壓力更敏感。噪音會隨著t值(或r值)增加而大大的降低到一定程度，當流量不再明顯變化時，噪音的變化也跟著趨緩。

The computer CPU speed has been greatly increased in recent years due to a rapid progress in semi-conductor technologies. The chip surface heat flux is thus higher and higher accordingly. It is becoming a critical challenge on how to remove the heat so that the system can be run reliably. The compact space with high flow resistance in a notebook computer environment is even more critical in the heat removal. Centrifugal flow fan with higher air pressure is frequently chosen under such a consideration.

Not only the blade angle, but also the volute has direct influences on centrifugal fan performance. The flowfield near the tongue has large unsteady characteristics, including pressure fluctuations. The purpose of the present study is to experimentally investigate the tongue influence on performance and noise. The approach is to measure the fan performance curve and noise level with different gaps (t) (and radii (r)), while the basic fan dimension is unchanged.

The measured data indicate that the maximum flow increases with t and r until certain limit values. The maximum air pressure drops with t and r slightly and then goes up. The degree of maximum air pressure variation is less than that of the maximum flow rate. The noise is more sensitive than the maximum flow and pressure. It drastically drops with t and r till certain vale when the maximum flow rate does not have significant change.

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