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

Abstract

Flow and heat transfer property simulation was performed on both helical and segmental baffle electric heaters of equilateral tube layout with one-plus-two U-tube units. Four helical baffle electric heaters have folded circumferential overlapped baffles with inclined angles of 20°, 25° and 30° single thread and 30° dual threads respectively, while two segmental ones have baffle plate spans of 200 and 250mm respectively. The folded baffle is designed to create two “ears” perpendicular on the axis of the cylinder by folding the inclined baffle at both corners of the curved edge and straight edges to fix the helical baffles with three sets of rod and spacing sleeve assembles. Simulation results show that the optimal inclined angle of helical electric heater is 25°, which has the highest comprehensive index and high heat transfer coefficient with low tube surface temperature, while the segmental baffle scheme with greater span has lower heat transfer coefficient and pressure drop but higher tube surface temperature. Compared with those of segmental scheme with baffle span of 200mm, 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 45.6K respectively.