🎓 Lesson 13
D5
Quantifying External and Internal Diffusion Effects
External diffusion is how fast reactants move from the bulk fluid to the catalyst surface, while internal diffusion is how fast they travel through the pores inside the catalyst particle.
🎯 Learning Objectives
- ✓ Calculate the external mass transfer coefficient (k_c) using dimensionless correlations (e.g., Sherwood–Reynolds–Schmidt)
- ✓ Determine the effectiveness factor (η) for first-order reactions in spherical catalysts using the Thiele modulus (φ)
- ✓ Analyze when internal diffusion limitations dominate by comparing η values and identifying pore diffusion-controlled regimes
- ✓ Apply Weisz-Prater and Mears criteria to diagnose external and internal diffusion limitations experimentally
- ✓ Explain how catalyst pellet size, porosity, and pore tortuosity influence observable reaction rates in industrial reactors