Thermal characteristics of perforated self-rotating twisted tapes in a double-pipe heat exchanger

Highlights: • Perforated self-rotating twisted tapes performed better than perforated stationary twisted tapes. • Thermal performance factor tended to increase sharply at initial stage of rotation behavior. • Increase in perforation ratios could improve heat transfer performance for given cases. • Some correlations varying with perforation ratio were established within 10% deviation. • Perforated self-rotating twisted tapes are an alternative choice to raise thermal performance factor. -- Abstract: The present study experimentally investigated thermal characteristics of a double-pipe heat exchanger fitted with perforated self-rotating twisted tapes with six perforation ratios of 0%, 1.16%, 3.63%, 6.46%, 10.1% and 14.49%. The experimental results showed that perforation ratio significantly affects the initial stage of rotation behavior and rotational speed. Perforated self-rotating twisted tapes were experimentally shown to perform greater thermal performance than perforated stationary twisted tapes. In addition, the increase in perforation ratios raised the Nusselt number and pressure drop. Higher thermal performance factor of PR = 10.1% than PR = 14.49% under rotating condition could be found. When the self-rotating twisted tapes varied from stationary to rotating condition, it is observed that thermal performance factor increased from 0.862 to 0.924, 0.987 to 1.025, 1.04 to 1.078, 1.084 to 1.101, and 1.042 to 1.055, for perforation ratios of 0%, 1.16%, 3.63%, 6.46%, and 10.1%, respectively. Finally, some correlations associated with perforation ratios were established to predict Nusselt number and friction factor, and perforated self-rotating twisted tapes were compared with perforated twisted tapes in terms of thermal performance factor. The optimal design of perforated self-rotating twisted tapes with proper perforated ratio could be offered for industrial application based on thermal performance evaluation.