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Purpose: Conventional electric heaters mostly use U-shaped electric heating tubes and the hollow tube electric heaters are new type ones that rely on the heat transfer tubes as heating elements. However, in the original design, the fluid flows through the annular gaps between the shell wall and the supporting plates, the chambers between supporting plates are generally stagnant zones. The purpose of study is to overcome these deficiencies. Design/methodology/approach: A modified approach is proposed in which the heating tubes are surrounded by holes on the supporting plates, thus the stagnant flow zone can be eliminated and the heating surfaces of both inside and outside the tube can be fully used. Numerical simulations were carried out on four schemes of hollow tube electric heaters, i.e. plate blocked, countercurrent, parallel and split. The results show that the two schemes of parallel and split can reduce the temperature difference between the two sides of the fixed tube plate, and thus reduce thermal stress and prolong the service life. Findings: The split scheme of electric heater has the highest comprehensive index, moderate heat transfer coefficient and minimum pressure drop on the shell side. Its average heat transfer coefficient and comprehensive index are, respectively, 15.7% and 52.9% higher and its average pressure drop and tube wall temperature are, respectively, 57.6% and 19 K lower than those of the original plate blocked scheme, thus it can be recommended as the best scheme of the hollow tube electric heaters. Originality/value: Based on the original design of hollow tube electric heater with plate blocked scheme, three plate perforated schemes were proposed and investigated. The thermal and flow features of the four schemes were compared in terms of heat transfer coefficient, pressure drop and comprehensive index ho·Δpo−1/3. The split scheme can reduce the temperature difference between two sides of the fixed tube plate with reduced thermal stress. It has moderate tube wall temperature and heat transfer coefficient, the smallest shell side pressure drop and the highest comprehensive index ho·Δpo−1/3, and it can be recommended as the optimal scheme. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• A novel helical baffle with small inclined angle and folded structure is proposed. • The new helical baffles can be created by cheap 2D laser cutting and folding. • The leakage between two folded helical baffles can be greatly decreased. • The novel electric heaters have excellent flow and heat transfer performances. • Folded helical baffles are more excellent at large equivalent angles in this work. The difficult manufacturing of helical baffles hinders the widespread application of the enhancement technology and the shortcut leakage between adjacent baffles impairs the enhancement effects. To solve these two issues, the promising anti-leakage and easy-to-manufacture helical baffles with small inclined angle and folded structure are proposed, which can be produced by 2D laser cutting and simple mechanical folding. The influence of different helical baffle configurations, including three normal helical schemes, three axial separation helical schemes, three novel folded axial separation helical baffle schemes and a segmental scheme on the performance of electric heaters are numerically investigated. The equivalent angles of helical schemes adopted in this work are 15°, 20° and 25°, and the inclined angle of helical baffles under axial separation connection style is 10°. Compared with the corresponding axial separation scheme without folding, the leakage can be significantly decreased, the heat transfer coefficients h and the comprehensive indices h ⋅Δ p −1/3 of FH15(10)°, FH20(10)° and FH25(10)° are increased by 6.5%/2.3%, 12.2%/7.3% and 20.4%/13.0%, and the averaged tube wall temperatures T w are decreased by 12.5 K, 25.4 K and 54.7 K, respectively. This research can provide feasibility for the extended application of helical baffles in electric heaters or heat exchangers. [ABSTRACT FROM AUTHOR]