Influence of key geometry parameters on heat transfer and flow resistance properties of toothed internal spiral piece cracking furnace tube

•A new type of open-tooth spiral is proposed.•Three different tooth angle structures were analyzed for heat transfer mechanism.•Field synergy and PEC analysis were utilized to evaluate the flow heat transfer.•α = 15° is the best opening angle for comprehensive heat transfer.•Toothed spiral tubes can improve the yield of key products. Strengthening the heat transfer technology of the furnace tube in the radiant section of the cracking furnace is very important in the field of energy-saving and environmental protection. This research proposes a new type of open-tooth spiral to enhance heat transfer and increase ethylene productivity. The mathematical computation has been conducted to evaluate the thermal-hydraulic performance with an open-tooth spiral. The classical Ordinary tube was also investigated for comparison. At the same time, the vortex identification method based on the Q criterion reveals the enhanced heat transfer mechanism of the open-toothed spiral tube. Then use the field synergy principle to qualitatively judge the heat transfer performance, combined with the comprehensive heat transfer evaluation factor (PEC) to quantitatively evaluate the comprehensive heat transfer performance of the open-tooth spiral tube. The results show that although the Nusselt number of the open-tooth spiral is 8%-10% lower than that of the ordinary screw, the friction resistance coefficient of the spiral tube with an opening angle of 15° can be reduced by 33%∼43%. Its PEC value is between 1.15 and 1.25, with excellent comprehensive heat transfer performance. It can effectively improve key products, such as ethylene, propylene, etc.