| Summary: | 碩士 === 國立中央大學 === 機械工程學系 === 101 === The purpose of research is to discuss how the thermal boundary layer changes its thickness in lower air velocity. With very low air velocity executed in the experiment, we have designed two types of fins, which are the louver fin and the offset strip fin to perform experiment with the following parameters.
Under the given air velocity at 0.5 m/s to 2.5 m/s and heat addition in 30 Watt, we fix the fin pitch in length of 1.2mm and vary two different louver length with two types of fins at 0.7 mm and 1 mm respectively to observe the main factor to affect the performance of our system. In addition, we also combine fan into our system so as to discuss if the selection of fans could better the heat transfer enhancement significantly.
From the result of pressure drops, the shear stress will become larger when reduced the louver length and the increase of the pressure drop in the offset strip fin. However, in the louver fin, the pressure drop is decreased with reducing the louver length. It is because the flow resistance also decreased with the louver length.
According to our experimental study, the flow structure of both the two types of fin in air velocity below 1 m/s have been fully developed. When the air velocity increase upper than 1 m/s, the changing of louver length have nothing to do with the performance.
If the same fan used in different type of fin , the volume flow rate will be different with the pressure drop. So we have to choose the fan that fitting the individual fin hoping the heat transfer performance is good as we designed.
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