| Summary: | 碩士 === 國立臺灣海洋大學 === 機械與機電工程學系 === 105 === This study placed six types of thermostatic cylinders of varying shapes inside a straight square tube. The cylinders were of two main types, two-dimensional and three-dimensional, with three subtypes each: circular, outer hexagonal, and inner hexagonal. A simulation was then conducted where, under varying temperatures and arrangements, the physical mechanism of a flow field passing through heated cylinders was studied. During the experiment, methods such as the hot-wire method, the schlieren technique, and thermocouples were used to study changes in the flow field resulting from the placement of different cylinders. The results revealed that the installation of hexagonal cylinders led to changes in the wake flow field, frequency, and turbulence intensity that enhanced cooling performance. Flow visualization demonstrated that with a two-dimensional cylinder, the wake flow exhibited a vortex structure; with a three-dimensional cylinder, the wake flow did not exhibit a vortex structure. Observations using the schlieren technique revealed that when the temperature was raised, the continuous structure of the two-dimensional flow field became compressed. When the three-dimensional flow field drew near the cylinder’s end faces, the continuous structure disappeared due to changes in turbulence intensity; some heat was also observed to have escaped from the end faces. Temperature distribution was then obtained by retrieving the temperatures of the wake, and the cooling performance of the cylinders was analyzed. The results show that when the flow field passed the cylinders, the structure of the downstream flow field changed, improving cooling performance. In comparison with a two-dimensional and a circular cylinder, an outer hexagonal cylinder increased cooling performance by 51.4% and an inner hexagonal cylinder did so by 6.5%. In comparison with three-dimensional cylinders, an outer hexagonal cylinder raised cooling performance by 50.57% and an inner hexagonal cylinder did so by 4.99%. Hexagonal cylinders on the whole were superior to circular cylinders for improving cooling performance. Moreover, the cooling performance of three-dimensional cylinders were superior to those of their two-dimensional counterparts: a three-dimensional circular cylinder increased cooling performance by 3.46% more than a two-dimensional circular cylinder, an outer hexagonal cylinder by 2.50%, and an inner hexagonal cylinder by 2.05%.
|
|---|
