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Summary

Sutida Phitakwinai, Wanich Nilnont — Recycling · This study evaluated the technical viability and thermodynamic performance of an open-loop upcycled heat pump dryer, repurposed from a decommissioned window-type air conditioner, for thin-layer red dragon fruit (Selenicereus costaricensis) drying. Experiments were executed at 50 °C under controlled air velocities (0.5, 1.0, and 1.5 m/s), using open-sun drying as a control. Mathematical modeling revealed that the Wang and Singh model best described the drying process (R2: 0.996368–0.999539). Accounting for volumetric shrinkage via equivalent average thickness (Leq = 0.75 L0), corrected effective moisture diffusivity (Deff) ranged from 1.194 × 10−9 to 3.138 × 10−9 m2/s, while convective mass transfer coefficients (hm) ranged from 5.241 × 10−7 to 1.880 × 10−6 m/s, both peaking at 1.5 m/s due to thinned concentration boundary layers. Thermodynamic assessments showed a maximum COPhp of 3.41 a