Abstract The flow and heat transfer performances were investigated on unilateral ladder type helical baffle heat exchangers (ULHBHXs) with different geometrical structures in half cylindrical space and compared with those of the segmental baffle heat exchangers (SBHXs). The unilateral ladder type helical baffles consist of two alternate groups of plates, the folded baffles (Baffles A) and the segment ones (Baffles B). The studied ULHBHXs include the combination schemes of different Baffle A with different baffle pitches (40, 60, 80 mm) and different projection length of inclined section (l = 60, 72, 84 mm and a plane one). Visualization methods of nephograms were adopted on special slices to clearly reveal the impacts of baffle configurations on flow patterns. The numerical results show that the shell-side heat transfer coefficients of the ULHBHX schemes with folded Baffles A are superior but the comprehensive indexes are inferior to those of the corresponding plane ones, and all the helical schemes are superior to those of the segmental schemes. The average ratios of shell-side heat transfer coefficient, pressure drop and comprehensive indexes hoΔpo−1 and hoΔpo−1/3 of all the twelve ULHBHX schemes over those of the SBHX ones with corresponding baffle pitches are 1.166, 0.670, 1.851 and 1.352, respectively.