Abstract: The flow and heat transfer performances are numerically simulated for four middle-axial-overlap trisection helical baffle heat exchangers with 36° baffle incline angle, approximate spiral pitch and equilateral triangle tube layout, including one scheme without block plates (36°MO), one scheme with the outermost strip notches blocked (36°MOB1), one scheme with outer triangle notches blocked (36°MOB2) and one scheme with all notches blocked (36°MOBA). The meridian slices M1 and unfolded concentric hexagonal slices H2 and H3 are constructed to obtain the full-angular view of shell-side flow characteristics by using pressure or velocity contours plus velocity vectors. The results show that the leakage patterns of the four schemes on concentric hexagonal slices H2 and H3 located respectively in outer and inner triangles of X-notch are quite different; each baffle chamber contains secondary flow, but the secondary flow of 36°MOB2 scheme is the strongest. Both heat transfer coefficient and pressure drop increase with the increase in blocked area, but in term of shell-side comprehensive performance ho/Δpo, the 36°MOB1 and 36°MOB2 schemes rank the first and second highest, while that of 36°MO scheme falls to the last. The average values of shell-side heat transfer coefficient ho and shell-side comprehensive performance ho/Δpo for 36°MOB1, 36°MOB2 and 36°MOBA schemes are 36.76%, 38.59%, 41.13% and 19.88%, 10.14%, 9.30% higher than those of 36°MO scheme. The 36°MOB1 scheme possesses strong application promise because of its better comprehensive performance and feasibility in installation of the outmost block plates on the tube bundle.

Key words: trisection helical baffle heat exchanger;numerical simulation;middle-axial-overlap;X-notch;block plate