| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 107 === This work investigates heat transfer enhancement due to flow disturbing rods in an air-to-water spiral heat exchanger. The air-side and water-side channel spacings are 10 and 1 mm, respectively. Totally 15 M4- thread rods are installed along the spiral section of the air channel. At seven different air volume flow rates (0.2, 0.4, 0.6, 0.8, 1.0, 1.2 and 1.4 m3/min), specific to the condition with or without flow disturbing rods, the fluid friction and heat transfer data are measured and the correlations between these data and the Reynold number (Re) are obtained, respectively. The result shows that, at 4000≦Re≦24000, the Nusselt number augmentation index (r1) for the entire heat exchanger (including the inlet and the spiral channel) is between 1.42 and 1.60; for only the spiral channel, the r1 value is in the range of 1.65 to 2.04 . This indicats that the flow disturbing rods are quite effective for enhancing the heat transfer in the spiral heat exchanger. The r2 value (ratio of Nu augmentation to fluid friction augmentation) for the entire heat exchanger is between 0.351 and 0.425; for the spiral channel, it ranges from 0.205 to 0.249.The experimental data are also compared to two sets of data previously obtained in the same laboratory. One corresponds to using 7 M4-thread rods and the other corresponds to using 7 M6-threaded rods. The r1 value for the current arrangement is much larger than the former, while it is close to the latter. Nervertheless, the r2 value for the current arrangement is larger than the latter.
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