533 / 2019-01-08 23:43:44

Heat transfer enhancement and pressure loss characteristics in a circular tube mounted with quadruple twisted-tapes

Heat exchanger, heat transfer, heat transfer enhancement, quadruple twisted tape, thermal performance

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Twisted tape swirl generator inserts extensively appear in a heat exchanger tube for redeveloping the velocity and thermal boundary layers, inducing single/multiple swirl flows and therefore enhancing the heat transfer rate and thermal performance. From the past decades, twisted tapes swirl generators have been used in a compact heat exchanger due to its low cost of material, ease of maintenance and manufacture. In the current investigation, the heat transfer, pressure loss and thermal performance factor behavior are reported in a heat exchanger mounted with quadruple twisted tape. The effect of quadruple twisted tape with various twist ratios (y/w) of 2.0, 3.0, 4.0 and 5.0 are studied in a round tube under constant wall heat flux condition. In order to investigate the effects of the twist ratio, four quadruple twisted tapes were employed in turbulent flow regime with Reynolds number between 5000 and 18,000 by using air as test fluid. from the results, the heat transfer rates in the tube mounted with quadruple twisted tape at y/w = 2.0, 3.0, 4.0 and 5.0 are respectively improved up to 73.2%, 67.5%, 59.3% and 54.1% of that in the plain tube. Similarly, the increase in friction factors for quadruple twisted tape at y/w = 2.0, 3.0, 4.0 and 5.0 are 8.2, 7.4, 6.5 and 5.4 times of the plain tube, respectively. Further, the twisted-tube yields higher heat transfer rate and pressure loss than the single twisted tape up to around 24% and 53%, respectively. For all quadruple twisted tape inserts, the empirical correlations were established for Nusselt number (Nu), friction factor (f) and thermal performance factor along with plain tube and the obtained correlations are mounted with the experimental data. Under the constant pumping power, the highest thermal performance factor gave is 1.41, 1.35, 1.32 and 1.27 respectively, for quadruple twisted tape with various twist ratios (y/w) of 2.0, 3.0, 4.0 and 5.0. Hence, the quadruple twisted tape swirl generators that performs higher energy efficiency along with lower operating cost is suggested for practical heat transfer enhancement applications, Furthermore, it is found also seen that the a heat exchanger mounted with quadruple twisted tape has an advantage in the lower Reynolds number between 5000 and 7000.