Numerical Simulation of Heat and Mass Transfer in Sludge Low-Temperature Drying Process.

Area of Science:

• Environmental Engineering
• Chemical Engineering
• Materials Science

Background:

• Sludge drying is crucial for waste management and resource recovery.
• Existing models often struggle to accurately simulate sludge drying, especially at intermediate moisture contents.
• Low-temperature drying presents unique challenges due to slower mass and heat transfer rates.

Purpose of the Study:

• To develop and validate an improved simulation model for sludge drying under low-temperature conditions.
• To investigate the influence of sludge cracking and shrinkage on drying dynamics.
• To elucidate the dominant mechanisms governing sludge drying at different stages.

Main Methods:

• Simulation using a modified sludge mass transfer flux model.
• Incorporation of novel cracking and shrinkage coefficient models dependent on sludge moisture content.
• Modification of effective diffusion and mass transfer coefficients.
• Comparison of simulation results with experimental data.

Main Results:

• The initial model showed discrepancies at sludge moisture content between 0.4-0.6.
• The refined model, including moisture-dependent coefficients, reduced the maximum error between simulation and experiment to 23.78%.
• Heat transfer and diffusion are dominant in the initial drying phase, with diffusion becoming primary after 30 minutes.

Conclusions:

• The proposed model significantly enhances the accuracy of simulating low-temperature sludge drying.
• Sludge cracking and shrinkage are critical factors influencing drying kinetics.
• Understanding the interplay of heat transfer and diffusion is key to optimizing sludge drying processes.