發明說明： 【發明所屬之技術領域】 本發明係涉及一種離心風扇，尤係涉及一種對發熱電 子元件散熱之離心風扇，本發明還涉及一種具有該離心風 扇之散熱裝置及使用該散熱裝置之電子裝置。 【先前技術】 隨著中央處理器（CPU)等電子元件功率之不斷提高， 散熱問題越來越受到人們之重視，在筆記型電腦中更是如 此。為在有限之空間内高效地帶走系統所產生之熱量，目 月’J業界主要採用由散熱縛片組、熱管及離心風扇組合之方 式進行散熱。該方式之熱傳導路徑為：CPU產生之熱量經 熱管傳至散熱鰭片組，再由離心風扇產生之氣流將傳至散 熱鰭片組之熱量帶走，所以離心風扇對系統之散熱性能有 非常大之影響。 為在有限之空間内更好地提高散熱裝置之散熱性能， 目月U主要針對散熱裝置之離心風扇之葉片參數、殼體曲線 形狀、馬達设计參數等進行優化設計，以期達到合理之組 合，故離心風扇各變數如何設計亦就顯得尤為重要。 在離心風扇設計中，風扇之風量係一個很重要之灸 數’而現實中風量之風壓與劈音又係—對矛盾關係，故對 風扇進行優化設計之難度較高。目前對風扇之眾多參數比 如葉片參數、馬達設計錢等進叙肢設計方式均需要 較大幅度地提箱造縣，導致優化設狀轉效益低下。 【發明内容】 有鑒於此，有必要提供一種在不增加成本之基礎上即 可增大空氣流量之離心風扇，同時亦有必要提供一種提升 散熱性能之散熱裝置及使用該散熱裝置之電子裝置。 一種離心風扇，包括一頂板、一底板、一轉子及設於 頂板與底板之間之一侧壁，該側壁上設有至少一出風口， 該頂板上設有一第一進風口，該底板上設有一第二進風 口，該頂板、底板及侧壁合圍形成一容置空間，該轉子設 于該容置空㈣，其巾該絲在對應轉子之細内朝向轉 子所在方向形成一凹陷。 種散熱裝置，包括一離心風扇及設於該離心風扇之 出風口之至少一鰭片組，其中該離心風扇包括一頂板、一 底板、一轉子及設於頂板與底板之間之一側壁，該側壁上 設有至少一出風口，該頂板上設有一第一進風口，該底板 上没有一第二進風口，該頂板、底板及侧壁合圍形成一容 置空間，該轉子設于該容置空間内，該底板在對應轉子之 範圍内朝向轉子所在方向形成一凹陷。 一種電子裝置’包括一機殼及設於該機殼内之一散熱 裝置，該機殼包括一上蓋及與該上蓋相對之一下蓋，該散 熱裝置包括一離心風扇及設於該離心風扇之出風口處之至 少一鰭片組，該離心風扇具有一頂板、與該頂板相對之一 底板及設於頂板與底板之間之一轉子，該離心風扇之頂板 上設有第一進風口，該離心風扇之底板上設有第二進風 口，其中該離心風扇之頂板距該機殼之上蓋之距離大於該 離心風扇之底板距該機殼之下蓋之距離，_心風扇之底 板在對應轉子之範圍内朝向轉子所在方向形成一凹陷。 與習知技術相比，上述離心風扇之底板在對應轉子之 範圍内朝向轉子所在方向形成—凹陷，#該離心風扇組褒 到電子裝置之機殼中時’使得底板之凹陷區域與機殼之下 蓋之間的距離增加，有利於更多空氣藉由第二進風口進入 離心風扇内，使離心風扇之總流量增加，從而提升散熱性 能。 【實施方式】 為適應可攜式電子裝置如筆記型電腦等朝向輕薄、短 小發展之需求，以及為實現快速散熱之目的，目前對其内 部發熱電子元件所使用之散熱裝置大多數採用配置離心風 扇之主動式散熱設計。 圖5所示為一種可攜式電子裝置5如筆記型電腦等， 該電子裝置5包括一機殼60及設於該機殼60内一散熱裝 置50，該散熱裝置5〇用於對電子裝置5内部之發熱電子 元件（圖未示）如筆記型電腦之中央處理器等進行散熱。 該機设60包括一上蓋61及一下蓋62。該散熱裝置5〇設 于該上蓋61與下蓋62之間，其包括一離心風扇51及一鰭 片組52。該鰭片組52設於離心風扇51之出風口 511處並 與發熱電子元件熱連接以吸收發熱電子元件所產生之熱 量。該離心風扇51包括一底座512、設於該底座512上之 一蓋板513及一轉子514 ’該轉子514設於該底座512内， 其運轉時產生之氣流吹向鰭片組52以將其吸收之熱量散 發。該蓋板513與底S犯上分別設有相對之-上進風口 515及下進風口 516以供外界氣流進入離心風扇51内。 該上、下進風口 515、516均為圓弧形且該上、下進風口 515 ' 516之半徑相等。 當散熱裝置50組裝到電子裝置5之機殼60内時，由 於機殼60之厚度有限，故使得離心風扇51之上進風口 515 與機殼60之上蓋61之間之上間距hl及離心風扇之下 進風口 516與機殼6〇之下蓋62之間之下間距腔均較小， 並且通常上間距hi會大於下間距h2。發明人利用cfd (Computational Fluid Dynamics，計算流體力學)軟體對上述 散=置5G置於電子裝置5中之工作情形進行不斷試驗及 流％核擬分析發現，從上進風口奶進人離心風扇&之風 里要退大於從下進風口 516進入離心風扇51之風量。如在 上間距hi為3.6mm，下間距h2為2 5mm時，計算得出上 進風口之流量為2.59efm，下進風κ流量為i 32伽，離 心風扇之總流量為3.91(^發明人研究發現離心風扇& 之進風π設計及賴口距電子裝置5之機殼6()之距離對離 心風扇51之進風流量有很大之關係。&，發明人積極對此 問題進行研究分析，輯圖在不需增加生産成本的基礎上 對離心風扇進行優化設計’來翻良好之散熱效果，乃有 本發明之誕生。 圖1所不為本發明散熱裝置1〇其中一較佳實施例之立 體分解圖’該散熱裝置10包括一離心風扇12、一第一鰭 片組14a及一第二鰭片組14b。該散熱裝置1〇適合於對筆 1321442 記型電腦等可攜式電子裝置中之發熱元件進行散熱。 該離心風扇12包括一頂板121、與頂板121相對之一 底板122、一轉子124及設於該頂板121與底板122之間 之一渦形之侧壁123。其中該侧壁123與底板122可藉由 壓鑄或注塑之方式一體製成。可以理解地，該側壁123亦 可與頂板121藉由壓鑄或注塑之方式一體製成。該離心風 扇12之頂板121、底板122及側壁123合圍形成一容置空 間，該轉子124設于該容置空間内。該轉子124包括一輪 轂125及自輪穀125週邊向外呈輻射狀延伸之複數葉片 126。該頂板121對應轉子124設有一圓形之第一進風口 127，以便外界空氣進入離心風扇12之容置空間内。該側 壁123與底板122相互垂直，該側壁123上開設有第一出 風口 132a及第二出風口 132b，該第一、第二出風口 132a、 132b均呈直線形且兩者相互垂直，如此設置可使離心風扇 12所產生之氣流從兩相互垂直之方向排出。該第一、第二 出風口 l32a、132b處對應設有第一、第二鰭片組14a、14b， 該第一、第二鰭片組14a、14b由複數散熱片堆疊而成，且 該第一、第二鰭片組14a、Mb之整體外形與第一、第二出 風132a、132b之形狀相一致。可以理解地，根據散熱需求 不同，該離心風扇12之出風口亦可僅設一個或兩個以上， 出風口之^狀可以為直線形、狐形或兩者之組合，所需韓 片組之數量及鰭片組之整體外形可根據出風口之數量及形 狀做相應之調整，以便與離心風扇12之出風口相匹配。 。月同時參照圖2至圖4，該離心風扇12之底板122具 10 1321442 有背向轉子124之一底面及面向轉子124之一頂面，其中 該底板122之頂面相對靠近離心風扇12之頂板121，而底 ' 板122之底面相對遠離離心風扇之頂板121。如圖2所示， 該底板122之底面在對應轉子124之範圍内有一下沉尺 寸，從而在底板122之底面上形成一凹陷i29a，且該凹陷 129a區域一直延伸至與離心風扇12之側壁123相接。在靠 近離心風扇12之侧壁123處，該凹陷129a區域背向轉子 • 124方向大设有一凸塊129c’該凸塊129c之高度與底板122 之底面平齊，該凸塊129c之設置可便於離心風扇12之定 位及安裝》在底板122之頂面上對應底面之凹陷129a區域 形成一凸起129b，如圖1所示。該底板122對應頂板121 之第一進風口 127設有一圓形之第二進風口 128，以便更 多之外界空氣進入離心風扇12内。在本實施例_，該第二 進風口 128之半徑大於第-進風口 127之半徑，以增加從 第二進風口 128進入之風量。另外，該第二進風口 128之 • 半徑亦可為與第一進風口 127之半徑相等。該第二進風口 128之中部設有一圓柱形之支撐部13〇，該離心風扇之 轉子124設於該支撐部130上，由於離心風扇12之底板 122之頂面在轉子124之範圍内形成有一凸起12卯，故離 心風扇12之轉子124與支撐部130均相應上移一定距離， 使得轉子124向離心風扇12之頂板121有所靠近。該支撐 部130藉由複數肋條131與底板m相連接，且這=肋^ 131將第二進風口 128分成複數部分。如圖4所示，這些 肋條m呈傾斜設置，使支撐部130相對於底板122之: 11 1321442 陷129a更朝向轉子124方向突出，從而該支撐部13〇之底 面在垂直方向上高於底板122之凹陷129a部分，有利於外 界空氣從第二進風口 128進入離心風扇12内。 圖4為圖1所示散熱裝置1〇置於一電子裝置丄之機殼 20内之剖視圖。該機殼2〇可為筆記型電腦等可攜式電子 裝置之外殼，其包括一上蓋21及與該上蓋21相對之一下 蓋22。該散熱裝置設于該上蓋21與下蓋22之間，其 中該離心風扇12之頂板121位於該機殼2〇之上蓋21與該 離心風扇12之底板122之間，且該離心風扇12之底板122 位於該機殼20之下蓋22與離心風扇π之頂板121之間。 該離心風扇12之頂板121與機殼20之上蓋21之間形成有 上間距（top gap) H1 ’該離心風扇12之底板122與機殼 之下蓋22之間形成有一下間距（bottom gap )H2。該上、 下間距HI、H2可分別作為外界空氣進入離心風扇14之第 苐一進風口 127、128之空氣流道。在本實施例中，離 心風扇12之頂板121與機殼20之上蓋21之間的上間距 H1之高度為3.6mm，離心風扇12之底板122之凹陷129a 區域與機殼20之下蓋22之間的下間距H2為3.4mm，而 位於第―、第二出風口 132a、132b附近該底板122無凹陷 12知之區域與機殼20之下蓋22之間的間距仍為2.5mm， 即藉由該凹陷129a之設置，使得該底板122與機殼20之 下蓋22之間的距離得以增加》藉由CFD數值模擬仿真實 驗’計算得出該離心風扇12之總流量為4.74cfm，與圖5 中所示之離心風扇51之總流量3.91cfm相比，在離心風扇 12 1321442 12之頂板121與機殼20之上蓋21之間的間距及離心風屬 12之底板122與機殼20之下蓋22之間的間距均保持不^ 之情況下，藉由在離心風扇12之底板122上設置該凹啗 129a，增大了該凹陷區域與機殼2〇之間之距離，使得離心 風扇12之總流量增長了 21.2%，可見，離心風扇12之性 能得到有效之提升。每一葉片126包括與輪轂125連接之 第一部分126a及遠離輪轂125之第二部分126b，該第一部 分126a在從輪轂125往第二部分126b之方向上高度逐哳 增加，這樣可使高度較大之第二部分126b吸入更多之氣 流。 本實施例中，由於離心風扇12之底板122之底面對應 離心風扇12之轉子124範圍内形成一凹陷129a區域。當 該離心風扇12組裝到電子裝置1之機殼2〇内時，使得離 心風扇12之底板122對應轉子124之區域與機殼20之下 蓋22之間的間距增加，有利於更多空氣藉由第二進風〇 128進入離心風扇12内，使離心風扇之總流量增加， 從而達到提升離心風扇12之散熱性能之目的。該底板122 在第一、第二出風口 132a、132b附近區域未設凹陷129a， 不至於減小第一、第二出風口 132a、132b之大小及減少第 、第一韓片組14a、14b設置之面積’這樣可使氣流流經 第一、第二出風口 132a、132b時保持較高之流速，有利於 快速之將第一、第二鰭片組14a、14b所吸收之熱量散發。 另外，該底板122上之凹陷129a部分可在加工底板122時 利用模具一次成型’無需增加製造成本。 13 1321442 综上所述，本發明符合發明專利要件，爰依法提出專 利申請。惟，以上所述者僅為本發明之較佳實施例，舉凡 熟悉本案技藝之人士，在爰依本發明精神所作之等效修飾 或變化，皆應涵蓋於以下之申請專利範圍内。 【圖式簡單說明】 圖1係本發明散熱裝置其中一較佳實施例之立體分解 圖。 圖2係圖1所示散熱裝置之立體組裝圖。 圖3係圖1所示散熱裝置另一角度之立體組裝圖。 圖4係圖1所示散熱裝置設於一機殼内之剖視圖。 圖5係基於改進之—散熱裝置置於—機殼内之剖視 圖。 【主要元件符號說明】 電子裝置 1 散熱裝置 10 離心風扇 12 頂板 121 底板 122 側壁 123 轉子 124 輪穀 125 葉片 126 第一部分 126a 第二部分 126b 第一進風口 127 第二進風口 128 凹陷 129a 凸起 12% 凸塊 129c 支撐部 130 肋條 131 第一出風口 132a 第二出風口 132b 第一 II片組 14a 第二鰭片組 14b 機殼 20 上蓋 21 下蓋 22 上間距 Hi 14 1321442 下間距 H2[Technical Field] The present invention relates to a centrifugal fan, and more particularly to a centrifugal fan for dissipating heat from a heat-generating electronic component, and to a heat sink having the centrifugal fan and an electron using the same Device. [Prior Art] As the power of electronic components such as a central processing unit (CPU) continues to increase, the problem of heat dissipation has received more and more attention, especially in notebook computers. In order to efficiently remove the heat generated by the system in a limited space, the industry has mainly used a combination of a heat-dissipating die set, a heat pipe and a centrifugal fan to dissipate heat. The heat conduction path of the method is: the heat generated by the CPU is transmitted to the heat dissipation fin group through the heat pipe, and the air flow generated by the centrifugal fan takes away the heat transferred to the heat dissipation fin group, so the centrifugal fan has a very large heat dissipation performance to the system. The impact. In order to better improve the heat dissipation performance of the heat dissipating device in a limited space, the main purpose is to optimize the design of the blade parameters, the shape of the casing curve and the motor design parameters of the centrifugal fan of the heat dissipating device, so as to achieve a reasonable combination. It is especially important to design the various variables of the centrifugal fan. In the design of the centrifugal fan, the wind volume of the fan is a very important number of moxibustions, and the wind pressure and the arpeggio of the actual mid-wind volume are contradictory, so it is more difficult to optimize the design of the fan. At present, many parameters of the fan, such as blade parameters, motor design money, etc., need to be put into the county in a large scale, resulting in low efficiency of optimization. SUMMARY OF THE INVENTION In view of the above, it is necessary to provide a centrifugal fan that can increase the air flow rate without increasing the cost, and it is also necessary to provide a heat dissipating device that improves heat dissipation performance and an electronic device using the same. A centrifugal fan includes a top plate, a bottom plate, a rotor and a side wall disposed between the top plate and the bottom plate, wherein the side wall is provided with at least one air outlet, and the top plate is provided with a first air inlet, and the bottom plate is provided There is a second air inlet, the top plate, the bottom plate and the side walls are enclosed to form an accommodating space, and the rotor is disposed in the accommodating space (4), and the wire forms a recess in a direction corresponding to the rotor in the corresponding rotor. The heat dissipating device includes a centrifugal fan and at least one fin set disposed at an air outlet of the centrifugal fan, wherein the centrifugal fan includes a top plate, a bottom plate, a rotor, and a side wall disposed between the top plate and the bottom plate. At least one air outlet is disposed on the side wall, the top plate is provided with a first air inlet, and the bottom plate does not have a second air inlet. The top plate, the bottom plate and the side walls are formed to form an accommodating space, and the rotor is disposed in the accommodating space. In the space, the bottom plate forms a recess in the direction of the rotor in the direction of the rotor. An electronic device 'includes a casing and a heat dissipating device disposed in the casing, the casing includes an upper cover and a lower cover opposite to the upper cover, the heat dissipating device includes a centrifugal fan and is disposed at the centrifugal fan At least one fin group at the tuyere, the centrifugal fan has a top plate, a bottom plate opposite to the top plate, and a rotor disposed between the top plate and the bottom plate, and the top of the centrifugal fan is provided with a first air inlet, the centrifugal The bottom of the fan is provided with a second air inlet, wherein the distance between the top plate of the centrifugal fan and the upper cover of the casing is greater than the distance from the bottom plate of the centrifugal fan to the lower cover of the casing, and the bottom plate of the heart fan is corresponding to the rotor A depression is formed in the direction toward the rotor. Compared with the prior art, the bottom plate of the centrifugal fan is formed in a direction corresponding to the rotor in the range of the corresponding rotor, and is recessed. When the centrifugal fan group is smashed into the casing of the electronic device, the recessed area of the bottom plate and the casing are The distance between the lower covers is increased, which facilitates more air entering the centrifugal fan through the second air inlet, so that the total flow of the centrifugal fan is increased, thereby improving the heat dissipation performance. [Embodiment] In order to meet the needs of portable electronic devices such as notebook computers, such as thin and short development, and for the purpose of rapid heat dissipation, most of the heat sinks used for internal heat-generating electronic components are configured with centrifugal fans. Active heat dissipation design. FIG. 5 shows a portable electronic device 5 such as a notebook computer. The electronic device 5 includes a casing 60 and a heat sink 50 disposed in the casing 60. The heat sink 5 is used for the electronic device. 5 The internal heating electronic components (not shown), such as the central processing unit of the notebook computer, are used for heat dissipation. The machine assembly 60 includes an upper cover 61 and a lower cover 62. The heat sink 5 is disposed between the upper cover 61 and the lower cover 62 and includes a centrifugal fan 51 and a fin set 52. The fin set 52 is disposed at the air outlet 511 of the centrifugal fan 51 and is thermally coupled to the heat generating electronic component to absorb the heat generated by the heat generating electronic component. The centrifugal fan 51 includes a base 512, a cover plate 513 disposed on the base 512, and a rotor 514. The rotor 514 is disposed in the base 512. The airflow generated during operation is blown toward the fin set 52 to The absorbed heat is emitted. The cover plate 513 and the bottom S are respectively provided with opposite-upper air inlets 515 and lower air inlets 516 for external airflow to enter the centrifugal fan 51. The upper and lower air inlets 515, 516 are all circular arc shaped and the upper and lower air inlets 515' 516 have the same radius. When the heat sink 50 is assembled into the casing 60 of the electronic device 5, since the thickness of the casing 60 is limited, the distance hl between the air inlet 515 above the centrifugal fan 51 and the upper cover 61 of the casing 60 and the centrifugal fan are made. The space between the lower air inlet 516 and the lower cover 62 of the casing 6 is smaller, and usually the upper pitch hi is greater than the lower spacing h2. The inventor used the cfd (Computational Fluid Dynamics) software to continuously test the operation of the above-mentioned 5G placed in the electronic device 5, and the flow analysis showed that the milk from the upper air inlet was entered into the centrifugal fan & The wind in the wind is to be retracted more than the amount of air entering the centrifugal fan 51 from the lower air inlet 516. For example, when the upper spacing hi is 3.6 mm and the lower spacing h2 is 2 5 mm, the flow rate of the upper air inlet is calculated to be 2.59 efm, the flow rate of the lower inlet κ is i 32 gamma, and the total flow of the centrifugal fan is 3.91 (^ inventor It has been found that the inlet π design of the centrifugal fan & and the distance from the casing 6 () of the electronic device 5 have a great relationship with the inlet flow rate of the centrifugal fan 51. & Inventors actively carry out this problem The present invention has been developed by analyzing and analyzing the optimized design of the centrifugal fan on the basis of no need to increase the production cost. FIG. 1 is not a preferred one of the heat dissipation device of the present invention. The heat dissipating device 10 includes a centrifugal fan 12, a first fin set 14a and a second fin set 14b. The heat dissipating device 1 is suitable for a portable type such as a pen 1314242 type computer. The heat generating component of the electronic device is configured to dissipate heat. The centrifugal fan 12 includes a top plate 121, a bottom plate 122 opposite to the top plate 121, a rotor 124, and a side wall 123 of a spiral formed between the top plate 121 and the bottom plate 122. Wherein the side wall 123 and the bottom plate 122 can be borrowed The die-casting or injection molding is integrally formed. It can be understood that the sidewall 123 can be integrally formed with the top plate 121 by die casting or injection molding. The top plate 121, the bottom plate 122 and the side wall 123 of the centrifugal fan 12 are enclosed to form an accommodation. The rotor 124 is disposed in the accommodating space. The rotor 124 includes a hub 125 and a plurality of blades 126 extending radially from the periphery of the valley 125. The top plate 121 is provided with a circular first corresponding to the rotor 124. The air inlet 127 is provided so that the outside air enters the accommodating space of the centrifugal fan 12. The side wall 123 and the bottom plate 122 are perpendicular to each other, and the side wall 123 is provided with a first air outlet 132a and a second air outlet 132b. The air outlets 132a, 132b are all linear and perpendicular to each other, so that the airflow generated by the centrifugal fan 12 can be discharged from two mutually perpendicular directions. The first and second air outlets l32a, 132b are correspondingly provided. a second fin set 14a, 14b, the first and second fin sets 14a, 14b are stacked by a plurality of heat sinks, and the overall shape and the first and second fin sets 14a, Mb are first Second wind The shapes of the flanges 132a and 132b are identical. It can be understood that the air outlet of the centrifugal fan 12 can be only one or two or more according to different heat dissipation requirements, and the shape of the air outlet can be linear, fox or both. In combination, the number of required Korean groups and the overall shape of the fin group can be adjusted according to the number and shape of the air outlets to match the air outlet of the centrifugal fan 12. Referring to Figures 2 to 4 at the same time, The bottom plate 122 of the centrifugal fan 12 has 10 1321442 having a bottom surface facing away from the rotor 124 and facing a top surface of the rotor 124. The top surface of the bottom plate 122 is relatively close to the top plate 121 of the centrifugal fan 12, and the bottom surface of the bottom plate 122 Relative to the top plate 121 of the centrifugal fan. As shown in FIG. 2, the bottom surface of the bottom plate 122 has a submerged size in the range corresponding to the rotor 124, so that a recess i29a is formed on the bottom surface of the bottom plate 122, and the recess 129a region extends to the side wall 123 of the centrifugal fan 12. Docked. Near the side wall 123 of the centrifugal fan 12, the recess 129a is provided with a protrusion 129c' facing away from the rotor 124. The height of the protrusion 129c is flush with the bottom surface of the bottom plate 122. The arrangement of the protrusion 129c can be facilitated. The positioning and installation of the centrifugal fan 12 forms a protrusion 129b on the top surface of the bottom plate 122 corresponding to the recess 129a of the bottom surface, as shown in FIG. The bottom plate 122 is provided with a circular second air inlet 128 corresponding to the first air inlet 127 of the top plate 121, so that more outer boundary air enters the centrifugal fan 12. In the present embodiment, the radius of the second air inlet 128 is larger than the radius of the first air inlet 127 to increase the amount of air entering from the second air inlet 128. In addition, the radius of the second air inlet 128 may be equal to the radius of the first air inlet 127. A cylindrical support portion 13 is disposed in the middle of the second air inlet 128. The rotor 124 of the centrifugal fan is disposed on the support portion 130. The top surface of the bottom plate 122 of the centrifugal fan 12 is formed in the range of the rotor 124. The projections 12 are so that the rotor 124 of the centrifugal fan 12 and the support portion 130 are both moved up by a certain distance, so that the rotor 124 is close to the top plate 121 of the centrifugal fan 12. The support portion 130 is connected to the bottom plate m by a plurality of ribs 131, and this = rib 131 divides the second air inlet 128 into a plurality of portions. As shown in FIG. 4, the ribs m are disposed obliquely so that the support portion 130 is opposite to the bottom plate 122: 11 1321442 The recess 129a protrudes toward the rotor 124 such that the bottom surface of the support portion 13 is vertically higher than the bottom plate 122. The recess 129a portion facilitates the passage of outside air from the second air inlet 128 into the centrifugal fan 12. 4 is a cross-sectional view of the heat sink 1 shown in FIG. 1 disposed within a casing 20 of an electronic device. The casing 2 can be a casing of a portable electronic device such as a notebook computer, and includes an upper cover 21 and a lower cover 22 opposite to the upper cover 21. The heat dissipating device is disposed between the upper cover 21 and the lower cover 22, wherein the top plate 121 of the centrifugal fan 12 is located between the cover 21 of the casing 2 and the bottom plate 122 of the centrifugal fan 12, and the bottom plate of the centrifugal fan 12 122 is located between the lower cover 22 of the casing 20 and the top plate 121 of the centrifugal fan π. A top gap H1 is formed between the top plate 121 of the centrifugal fan 12 and the upper cover 21 of the casing 20. A bottom gap is formed between the bottom plate 122 of the centrifugal fan 12 and the lower cover 22 of the casing. H2. The upper and lower spacings HI, H2 can respectively enter the air flow path of the first air inlets 127, 128 of the centrifugal fan 14 as outside air. In the present embodiment, the height H1 between the top plate 121 of the centrifugal fan 12 and the upper cover 21 of the casing 20 is 3.6 mm, and the recess 129a of the bottom plate 122 of the centrifugal fan 12 and the lower cover 22 of the casing 20. The lower spacing H2 is 3.4 mm, and the distance between the area of the bottom plate 122 without the recess 12 near the first and second air outlets 132a, 132b and the lower cover 22 of the casing 20 is still 2.5 mm, that is, by The recess 129a is disposed such that the distance between the bottom plate 122 and the lower cover 22 of the casing 20 is increased. The total flow rate of the centrifugal fan 12 is calculated to be 4.74 cfm by CFD numerical simulation experiment. The total flow rate of the centrifugal fan 51 shown in the figure is 3.91 cfm, the distance between the top plate 121 of the centrifugal fan 12 1321442 12 and the upper cover 21 of the casing 20 and the bottom plate 122 of the centrifugal wind 12 and the lower cover of the casing 20 The distance between the recessed area and the casing 2〇 is increased by providing the recess 129a on the bottom plate 122 of the centrifugal fan 12, so that the centrifugal fan 12 is The total flow increased by 21.2%. It can be seen that the performance of the centrifugal fan 12 is effectively improved. Rise. Each blade 126 includes a first portion 126a coupled to the hub 125 and a second portion 126b remote from the hub 125. The first portion 126a is increased in height from the hub 125 toward the second portion 126b, such that the height is greater The second portion 126b draws in more airflow. In this embodiment, the bottom surface of the bottom plate 122 of the centrifugal fan 12 forms a recess 129a region corresponding to the rotor 124 of the centrifugal fan 12. When the centrifugal fan 12 is assembled into the casing 2 of the electronic device 1, the spacing between the area of the bottom plate 122 of the centrifugal fan 12 corresponding to the rotor 124 and the lower cover 22 of the casing 20 is increased, which facilitates more air borrowing. The second air inlet 128 enters the centrifugal fan 12 to increase the total flow rate of the centrifugal fan, thereby achieving the purpose of improving the heat dissipation performance of the centrifugal fan 12. The bottom plate 122 is not provided with a recess 129a in the vicinity of the first and second air outlets 132a, 132b, so as not to reduce the size of the first and second air outlets 132a, 132b and reduce the setting of the first and second Korean sets 14a, 14b. The area 'this allows the airflow to flow through the first and second air outlets 132a, 132b to maintain a relatively high flow rate, which facilitates rapid dissipation of heat absorbed by the first and second fin sets 14a, 14b. In addition, the portion of the recess 129a on the bottom plate 122 can be molded once using the mold when the bottom plate 122 is processed' without increasing the manufacturing cost. 13 1321442 In summary, the present invention complies with the requirements of the invention patent and submits a patent application according to law. However, the above description is only the preferred embodiment of the present invention, and equivalent modifications or variations made by those skilled in the art will be included in the following claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective exploded view of a preferred embodiment of a heat sink according to the present invention. 2 is an assembled, isometric view of the heat sink shown in FIG. 1. 3 is a perspective assembled view of another angle of the heat sink shown in FIG. 1. 4 is a cross-sectional view showing the heat sink shown in FIG. 1 disposed in a casing. Figure 5 is a cross-sectional view of the improved heat sink placed within the housing. [Main component symbol description] Electronic device 1 Heat sink 10 Centrifugal fan 12 Top plate 121 Base plate 122 Side wall 123 Rotor 124 Valley 125 Blade 126 First portion 126a Second portion 126b First air inlet 127 Second air inlet 128 Depression 129a Bump 12 % Bump 129c Supporting portion 130 Rib 131 First air outlet 132a Second air outlet 132b First II piece 14a Second fin set 14b Case 20 Upper cover 21 Lower cover 22 Upper spacing Hi 14 1321442 Lower spacing H2
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