Experimental determination of dynamic pseudo-equilibrium moisture content: A practical limit for the drying process

Area of Science:

• Chemical Engineering
• Thermodynamics
• Material Science

Background:

• Industrial dryer design relies on mass, energy, and momentum balances.
• Existing models often oversimplify the final stages of drying, assuming immediate thermodynamic equilibrium.
• This simplification can lead to inaccurate predictions in dryer size and operation.

Purpose of the Study:

• To introduce the concept of dynamic pseudo-equilibrium moisture content (X).
• To present a method for experimentally determining X.
• To propose the use of a practical moisture ratio incorporating X for improved dryer modeling.

Main Methods:

• Experimental determination of drying curves for various materials.
• Analysis of drying stages: kinetic, transition, and equilibrium.
• Identification of the transition point to define X.

Main Results:

• The drying process exhibits a distinct transition stage before reaching thermodynamic equilibrium.
• The dynamic pseudo-equilibrium moisture content (X) accurately demarcates the end of the kinetic drying stage.
• Using X in the practical moisture ratio enhances model prediction accuracy, especially at lower temperatures.

Conclusions:

• The dynamic pseudo-equilibrium moisture content (X) is a critical parameter for understanding drying kinetics.
• Accurate dryer simulation and design necessitate the inclusion of this transition stage.
• The proposed practical moisture ratio improves the prediction capacity of drying models, preventing underestimation of dryer size and time.