Influence of outlet orientation and variable tube length on high temperature zones of U‐tube trisection helical baffle electric heaters

Numerical simulation was performed to optimize temperature distribution especially at high temperature zones at the rear part of U‐tube bundle electric heaters with unique one‐plus‐two U‐tube layouts. The influences of variable tube lengths and different outlet nozzle orientations on flow and thermal features on axial separation trisection helical baffle schemes in contrast to segmental schemes were investigated. The results show that the variable tube length schemes can effectively ameliorate high temperature zones and obtain more uniform temperature fields. The mean heat transfer coefficient, h.t.c., and tube wall temperature, Tw, of the variable tube length scheme HV15(10)°‐180° are respectively 0.7% higher and 3.1 K lower than those of the normal scheme H15(10)°‐180°. The optimal relative position of the outlet and tube bundle for helical schemes is that the outlet axis is not only tangent to the last straight edge of the baffle but is also on the side near it, while the optimum outlet angle for the segmental scheme is 90° within the research scope. Compared with segmental scheme S200‐90°, the averaged heat transfer coefficients, h.t.c.s, and comprehensive indexes, h · Δp−1/3, of the helical baffle schemes HV15(10)°‐180°/HV15(10)°‐Ax respectively rise by 14.6/11.8% and 16.1/13.8%, while the average Tw declines by 40.7/33.3 K.