1. Field of the Invention
The invention relates to a heat dissipation apparatus, and more particularly to a heat dissipation apparatus providing reduced noise.
2. Description of the Related Art
As performance of electronic devices is promoted, heat dissipation apparatuses or systems are indispensable and thus used in the electronic devices. If heat generated by an electronic device is not efficiently dissipated, performance of the electronic device may deteriorate or the electronic device may be damaged.
Fans serve widely as heat dissipation apparatuses. FIG. 1A is a schematic view of a conventional fan 1, and FIG. 1B is a schematic cross section taken along A-A′ of FIG. 1A. The conventional fan 1 is composed of a fan frame 11 and an impeller 12. When the fan 1 operates, the impeller 12 is activated by a motor 13, providing airflow to a heat source (such as a heat-generating electronic device, not shown) and thus dissipating heat therefrom. The fan frame 11 has a through hole forming an air inlet 112 and an air outlet 114 on two ends of the fan frame 11, respectively. The air inlet 112 is connected to the air outlet 114 by way of a central passage 116, such that the airflow provided by the impeller 12 can freely pass the air inlet 112 and air outlet 114. Additionally, four threaded holes 14 are formed on the corners of the fan frame 11, by means of which the fan 1 can be fixed to the shell of a system having electronic devices, such as a computer.
FIGS. 1C, 1E, and 1F are schematic cross sections of conventional fans and fan frames. A bevel angle C (as shown in FIG. 1C) or a tapered angle D (as shown in FIG. 1E) is formed near the air inlet 112 or air outlet 114 of the fan frame 11 in order to increase the area through which the airflow passes. As shown in FIG. 1D, although the bevel angle C increases the area of the air outlet 114, output airflow cannot be concentrated, thus reducing the airflow pressure provided by the fan frame 11. Alternatively, a recessed opening E (as shown in FIG. 1F) is formed near the air outlet 114 of the fan frame 11, increasing the area through which the airflow passes. However, the airflow is easily dispersed from the recessed opening E.
Conventionally, when airflow passes through the air outlet 114, the airflow directly contacts the periphery of the inner wall of the central passage 116 (as shown in FIG. 1B), bevel angle C, tapered angle D, or wall of the recessed opening E. Accordingly, the airflow can not pass through the air outlet 114 smoothly and is slowed. Also, noise is generated by friction between airflow and the inner peripheral wall of the central passage 116. Specifically, the higher the rotational speed of the fan, the more the noise generated thereby.