| Summary: | 碩士 === 國立中央大學 === 機械工程學系在職專班 === 103 === The purpose of this study is to propose and verify a design process for the impellers of an axial-flow fan to meet the heat dissipation requirements of a condenser system. A finite element analysis (FEM) technique is applied to determining the flow field and performing the structural analysis with a fluid-solid coupling method. The natural frequency is determined to make sure that resonance is not going to take place in operation of such a fan.
The key specifications for such an axial-flow fan include an air flow of 8580 m3/h and a wind pressure of 50 Pa. Through fluid dynamics analysis with FEA, a proper set of setting angle and airfoil is selected for the impeller geometry to meet the requirements at a fan speed of 950 rpm among five initial designs considered. A fabrication process using sheet metal, for reducing cost, is further considered in making the final design of the impellers. The final design of the sheet metal impellers is verified to meet the requirements in fluid mechanics by FEA simulation. Subsequently, a fluid-solid coupling FEA simulation is conducted to assess the structural integrity of the impeller design at a higher fan speed of 1050 rpm. As no structural failure is predicted by the simulation according to the von Mises criterion, a mockup of the impeller design is fabricated for testing. Experiments such as wind tunnel test, strain measurement for hub platform, and natural frequency measurement are then conducted on the mockup sample to evaluate its performance and stability and to verify the simulations.
Experiments and simulations, based on the specification of MACA 210-07, both verify that the sheet metal impellers designed in this study can meet the heat dissipation requirements of a condenser system. A good structural integrity is expected, as the safety factor for the components hub of platform, blade, washer, and bolt is 2.57, 2.14, 4.81, and 1.78, respectively. The natural frequency of the first modal vibration is 24.6 Hz which is higher than the maximum working fan speed of 1050 rpm (17.5 Hz). Accordingly, no resonance is expected to take place.
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