Enhancement Effect for Heat Transfer by Combined Use of Internally Grooved Rough Surfaces and Twisted Tapes

Abstract

The combined use of an internally grooved rough tube and a twisted tape was proposed as a technique for enhancing heat transfer in single-phase turbulent heat transfer. A remarkable increase in heat transfer efficiency was obtained when the heat transfer promoters satisfied the following conditions. 1) The tape should be counter-twisted against the rotation of the grooves. Better performance was obtained when the cross angle between the twisted tape and the groove was near 90 degrees. 2) Relative roughness of groove should be considerably large. Typically, 2.2% of relative roughness to the tube diameter gave better enhancement of heat transfer than the case of 1.1 % of relative roughness. The best performance of the heat transfer promoter proposed in this work can be stated as follows : The heat transfer coefficient at the same pumping power consumption reached 3.0-3.5 times larger than that of a smooth tube, and a 70-75% reduction of heat transfer surface compared with a smooth tube was obtained under conditions of the same pumping power and the same heat duty.