Heat transfer enhancement of folded helical baffle electric heaters with one-plus-two U-tube units

Circumferential overlapped helical baffles make all sector baffles contact peripherally to form a pseudo helical flow channel. This pseudo helical channel makes the zigzag fluid flow in segmental baffles change into spiral flow, and keeps the spiral flow almost constantly along the spiral direction. One-plus-two U-tube layout is a kind of commonly used equilateral triangle tube layout and can avoid the negative impact on flow caused by center fake tube in multi-circular layer layout. Compared with segmental scheme with baffle span of 200 mm, the heat transfer coefficient and comprehensive index of helical electric heater with inclined angle of 25° increase by 18.3% and 29.8% respectively, while the pressure drop and the average temperature on tube surface reduce by 24.3% and 45.6 K respectively.246