Thermal enhancement in a round tube with snail entry and coiled-wire inserts

Influences of the insertion of coiled wires in conjunction with a snail-type swirl generator mounted at the tube entrance on heat transfer and turbulent flow friction characteristics in a uniform heat-flux, circular tube are experimentally investigated. In the present work, the coiled wire used as a turbulator is placed inside the test tube using air as the test fluid while the snail is employed to create a decaying swirl flow at the tube inlet. The effects of the snail entry and insertion of two different wire-sections of coils: square and circular, with a fixed pitch ratio on heat transfer rate in the tube are examined for the Reynolds number ranging from 5000 to 25,000. The experimental results are compared with those obtained from using coiled wire/snail entry alone, apart from the smooth tube. The results reveal that the presence of coil-wires together with the snail leads to a considerable increase in heat transfer and friction loss over the smooth tube. The snail entry with the coiled square-wire provides higher heat transfer rate than that with the circular one under the same conditions. Also, performance evaluation criteria to assess the real benefits in using both the coil-wire and the snail entry of the enhanced tube are determined.