The main mechanism of efficient performance of heat transfer enhancement in circumferential overlap trisection helical baffle heat exchangers is investigated.The heat exchanger possesses not only the general characters of helical baffle heat exchangers but also the features that are suitable for equilateral triangles layout of tubes and avoid the shortcut in triangular zones of adjacent baffles.It is the row of tubes at the junction triangle of adjacent baffles that effectively dampers the reverse leakage driven by differential pressure between upstream and downstream chambers

which makes this type of helix heat exchangers even more efficient than the others.The test results for heat transfer performance are presented for circumferential overlap trisection helical baffle heat exchangers with single thread schemes of baffle tilt angles of 20°

24°

28°

32°

and dual thread scheme of baffle tilt angle 32°

in contrast to a segmental baffle heat exchanger.The results show that the optimum scheme within the testing scope is the one with baffle tilt angle of 20°

and the ratios of the mean values of shell side heat transfer coefficient

pressure drop

and comprehensive index(ho/Δpo) of the helical scheme with baffle tilt angle of 20° over those of the segmental baffle scheme are 1.122

0.566 and 2.035 respectively.The dual thread scheme of baffle tilt angle 32° has higher heat transfer coefficient

pressure drop and the comprehensive index(ho/Δpo) than the single thread one with same tilt angle.