Numerical simulation study on dew point control in the local area of a vertical continuous annealing furnace

• Two kinds of humidifying tube structures, nested double-layer current-sharing tube and oblique single-layer current-sharing tube, were designed. • The influence of two kinds of humidification pipe structures on the dew point in the furnace was studied and analyzed. • The synergistic effect of humidifying pipe structure, partition wall and radiation shield structure on dew point is studied and analyzed. • A dimensionless formula for evaluating the uniformity of dew point in furnace is obtained. • The influence of strip speed on dew point was studied. To address the issue of uneven humidifying gas distribution in continuous annealing furnaces, which affects the quality of strip galvanizing, a mathematical model of humidifying gas convection and diffusion within the furnace was developed. Experimental and numerical analyses of flow characteristics in humidifying tubes were conducted, focusing on nested double-layer equalizing tubes and oblique single-layer equalizing tubes. The effects of humidification tube design on gas convection and diffusion uniformity were compared, and the coupled influence of heat shield and partition wall structures on heated gas behavior was also evaluated. Results indicated that the nested double-layer equalizing tube significantly reduced airflow segregation and improved atmosphere uniformity, enhancing humidification performance when combined with optimized furnace architecture. Transient simulations and parameter optimization identified the optimal configuration as “improved furnace structure + nested double-layer equalizing tube(hole up).” This combination reduced the standard deviation of the dew point to 3 °C and increased the average dew point uniformity index to 0.90.