Influence of thermal pulse regimes on drying kinetics and energy–exergy performance of hot-air dried pineapple slices

This study evaluates the effects of thermal pulse regimes on drying kinetics, thermodynamic performance, and physical quality changes during hot-air drying of pineapple slices. A modified intermittent hot-air drying (IHAD) strategy was developed, in which a constant base air temperature of 60 °C was maintained while short-duration thermal pulses were periodically applied under different pulse frequencies. Drying behavior was described using thin-layer models, all of which showed excellent agreement with experimental data ( R ² > 0.996), with the Midilli model providing the best fit. Drying occurred predominantly in the falling-rate period, and pulse-assisted operation enhanced drying kinetics. Among the tested conditions, TPR8 exhibited the highest drying rate constant and the fastest moisture removal. Thermodynamic performance was assessed using the Energy Utilization Ratio ( EUR ) and exergy efficiency ( η e x ). Compared with continuous drying, pulse-assisted regimes significantly improved both indicators. The maximum EUR increased from 81.98% to 89–91%, while η e x increased from 6.56% to approximately 10.0–10.6%. The highest cumulative exergy performance was observed at TPR10. Physical quality evaluation showed that thermal pulse drying influenced shrinkage to some extent, while color change remained statistically similar among treatments. Shrinkage values ranged from 70.59 to 82.46%, whereas total color difference (∆ E ) values ranged from 24.77 to 27.03. Significant differences were observed only in shrinkage, with TPR8 showing the lowest value, while no significant differences were found for color change among drying conditions. These results indicate that intermittent thermal pulsing improved drying kinetics and thermodynamic performance without adversely affecting color quality, although its effect on shrinkage was limited but measurable. Overall, the proposed pulse-assisted drying strategy improved both drying kinetics and thermodynamic efficiency while maintaining acceptable physical quality, demonstrating its potential as an effective approach for enhancing the performance of hot-air drying systems.