Passive heat transfer enhancement techniques are one of the most interesting approaches to increase the thermal efficiency of heat transfer apparatuses since they do not require external power. Between them, twisted-tape inserts are a very economical technique that can be easily installed in an already working plant in order to increase its thermal performance. The aim of the present work is to experimentally investigate the heat transfer augmentation mechanism induced by the insertion of twisted tapes. The heat transfer performance of the twisted-tape inserts is compared with that of coiled pipes, whose effect on heat transfer is based on the onset of swirl components into the flow as it happens for twisted tapes devices. The two heat transfer enhancement mechanisms have been deeply investigated by using different fluids in order to obtain a robust comparison both for the laminar and the turbulent flow regime.
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