Effects of structural configurations in bidirectional airflow bulk curing barns on curing uniformity, energy consumption, and quality of tobacco leaves

This study aims to investigate the impact of airflow direction and spatial configuration in an intensive drying barn on temperature-humidity uniformity, tobacco leaf physical properties, quality, and energy consumption, using K326 mid-leaf tobacco as the test material. Three barn types were evaluated: the downward-airflow biomass bulk curing barn (CK), the conventional bidirectional-airflow barn (T1), and the vertical-square bidirectional-airflow barn (T2). Temperature-humidity distribution, tobacco leaf physical properties, cured leaf quality, and energy consumption during drying were assessed. Results showed that during color-fixing and stem-drying stages, T1 and T2 achieved greater temperature-humidity homogeneity than CK, with T2 reducing horizontal and vertical differentials more effectively. T1 reduced the temperature-humidity coefficient of variation by 42.86%–67.86% compared to CK (p < 0.05). Tobacco leaf dehydration and shrinkage followed a “slow-fast-slow” pattern during curing, peaking at the early color-fixing stage (84–96 h), T2 exhibited the highest water loss rate, followed by CK and T1. However, overall dehydration and shrinkage throughout the entire curing process ranked as T2 > T1 > CK. Bidirectional airflow circulation barns (T1 and T2) enhanced the accumulation of neutral aroma compounds and polyphenols, with T2 showing the most pronounced benefits. Additionally, T1 significantly increased the content of four major degradation products (e.g., plastid pigments) by 13.52%–56.27% compared to CK (p < 0.05). Economic traits and sensory quality evaluations ranked the barns as T2 > T1 > CK. T1 increased the percentage of premium-grade leaves and the average price by over 10% compared to CK, although these values remained lower than those of T2. Bidirectional airflow barns reduced curing energy consumption, with T1 lowering biomass fuel use, electricity consumption, and curing time by 6.98%–19.31% relative to CK, though it was less efficient than T2. Bidirectional-airflow barns, especially vertical-square configurations, enhanced temperature-humidity uniformity. This facilitated water evaporation and leaf deformation during curing, increased neutral aroma compounds and polyphenols, improved sensory quality, reduced energy consumption, and elevated economic traits.