Heat and Mass Transfer and Cracking Stress Analysis of the Soybean During Variable‐Temperature Hot Air Drying

ABSTRACT As an important grain and oil crop, the drying quality of soybeans is critical for storage stability. However, conventional constant‐temperature drying often induces cracking due to localized stress concentration. Existing studies primarily focus on simulating stress fields but lack a quantitative correlation with the material's actual failure limit. To bridge this gap, this study investigates the mechanism of variable‐temperature drying by establishing a coupled heat‐mass transfer and stress evolution model, applying an experimentally derived, moisture‐dependent dynamic cracking stress threshold curve to validate the cracking behavior. The model was rigorously validated, showing maximum deviations of only 7.1% for temperature and 8.9% for moisture content. Based on this framework, the variable‐temperature drying strategies were optimized. Quantitative analysis revealed that: (1) In terms of efficiency, the temperature‐decreasing strategy (60°C → 50°C → 40°C) reduced the drying time to 160 min, a 46.7% reduction compared to the constant‐temperature 40°C mode (300 min). (2) In terms of the mechanism, the simulation results show that the crack stress curve is the failure criterion, and the crack will occur when the stress perpendicular to the embryo axis reaches 10.5 MPa in constant‐temperature 40°C mode. In contrast, the temperature‐decreasing mode maintained the maximum stress at 8.25 MPa, successfully keeping it within the Stress‐Strength safety margin. These findings provide a mechanism‐based theoretical foundation, demonstrating that aligning the drying driving force with the seed's evolving mechanical strength is the key to achieving high‐efficiency, low‐damage drying.