Abstract:

In order to enhance the heat transfer, a method that combines the converging-diverging tube and the spaced twisted tape was presented, and the heat transfer characteristics and flow resistances of four converging-diverging tubes with spaced twisted tapes being inserted in four different spaces were experimentally investigated. The results were then compared with those of the smooth circular tube with or without the twisted tape and the converging-diverging tube without twisted tape. Experimental results indicate that the heat transfer is more greatly enhanced with the Reynolds number increasing in the range of 3400 to 20000, and that, when the twisted tapes with a length of 68 mm and a rotation angle of 180 are inserted in the converging-diverging tube with a space of 700 mm, the tube possesses the best heat transfer performance and the valuation factor of heat transfer respectively increases by 21% , 15% and 16%, as compared with those of the three other above-mentioned tubes. It is thus concluded that the inserting of spaced twisted tapes may greatly enhance the heat transfer performance of the converging-diverging tube.

Key words: heat transfer enhancement, twisted tape, converging-diverging tube