The flow and heat transfer characteristics of a novel kind of loose-fit twisted insert (CLT) are studied by RNG k-ε numerical method. The verification has been conducted to compare the numerical and the experimental results of Manglik and Bergles. The difference of flow and heat transfer characteristic is investigated by comparing between CLT and corrugated tube with loose-fit twisted tape insert (SLT). Finally

the effect of twisted ratio and clearance ratio for the flow and heat transfer characteristics is investigated in CLT. The results show that compared with the traditional SLT

the heat transfer performance in CLT increases by 1.17 times and the maximum increasing of absolute value for overall heat transfer performance is 0.15. The overall heat transfer performance in CLT increases with the increasing twisted ratio

but the increasing slope decreases gradually

meanwhile

the decreasing extent is more obvious in high Reynolds number. Meanwhile

the overall heat transfer performance in CLT decreases with the increasing clearance ratio

and the decreasing slope also decreases gradually. The decreasing extent is very obvious at the range of low Reynolds number

however

the values of overall heat transfer performance decrease slightly at the range of high Reynolds number. Take into consideration for various factors

low clearance ratio of twisted tape should be selected at the range of low Reynolds number

the high one is suitable for high Reynolds number.