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This paper deals with the experimental investigation on Nusselt number,friction factor and thermal en-hancement factor of a double pipe heat exchanger equipped with twisted tape consisting wire nails(WN-TT) and plain twisted tapes(P-TT) with three different twist ratios of y 2.0,4.4 and 6.0. Test runs are conducted using the water as the working fluid with Reynolds number range between 2000 and 12000 for WN-TT and P-TT. It is found that Nusselt number,friction factor and thermal enhancement factor in the tube equipped with WN-TT appreciably higher than those in the tube fitted with P-TT and plain tube. Over the range considered Nusselt number,friction factor and thermal enhancement factor in a tube with WN-TT are respectively,1.08 to 1.31,1.1 to 1.75 and 1.05 to 1.13 times of those in tube with P-TT. The better performance of WN-TT is due to combined effects of the follow-ing factors:(1) common swirling flow generated by P-TT,(2) additional turbulence offered by the wire nails. Em-pirical correlations for Nusselt number,friction factor and thermal enhancement factor are also formulated from the experimental results of WN-TT and P-TT.
This paper deals with the experimental investigation on Nusselt number, friction factor and thermal en-hancement factor of a double pipe heat exchanger equipped with twisted tape supplemental wire nails (WN-TT) and plain twisted tapes (P-TT) with three different twist ratios of y 2.0, 4.4 and 6.0. Test runs are conducted using the water as the working fluid with Reynolds number range between 2000 and 12000 for WN-TT and P-TT. It is found that Nusselt number, friction factor and thermal enhancement factor in the tube equipped with WN-TT appreciably higher than those in tube fitted with P-TT and plain tube. Over the range considered Nusselt number, friction factor and thermal enhancement factor in a tube with WN-TT are respectively, 1.08 to 1.31 , 1.1 to 1.75 and 1.05 to 1.13 times of those in tube with P-TT. The better performance of WN-TT is due to combined effects of the follow-ing factors: (1) common swirling flow generated by P-TT, ( 2) additional turbulence offered by the wire nails. Em-piri cal correlations for Nusselt number, friction factor and thermal enhancement factor are also formulated from the experimental results of WN-TT and P-TT.