COMPARISON OF HEAT TRANSFER CHARACTERISTICS OF WATER IMPINGING FLOW WITH A SINGLE CIRCULAR NOZZLE AND AN INSERT TYPE SWIRLING NOZZLE

摘要

Conventional impinging jets enhance heat transfer but produce non-uniform radial distributions of the local and surface Nusselt numbers. In attempt to improve the radial uniformity of heat transfer, many researchers have introduced the concept of the swirling flow. The swirling flow can be generated by strips or swirling generators. The swirling generator is a circular rod with helical blades. The swirling generator is inserted inside a tube. This swirling generator with helical blades can generate swirling flow at the outlet of the nozzle. First of all, flow visualization of swirling jet as varying swirling angles, the length of the swirl generators, and distance between nozzle exit and a swirl generator is investigated. Based on the flow visualization, it is found that the distance between nozzle exit and a swirl generator affects the performance of swirling jet. For heat transfer analysis, an induction heating method is used to heat a steel plate up to a certain level which is almost the same as temperature of steel in iron-and steelmaking processes. For obtaining temperature distribution on impinging surface, several thermocouples are inserted below 1mm from the surface of the sample. Based on temperature distributions on the surface of a sample, 2-D temperature contours are obtained according to time. Based on the contours, effect of distance from nozzle exit to a swirling generator on uniform cooling is investigated.