Internal diffusion is typically modeled using the Thiele modulus and the effectiveness factor. The Thiele modulus (φ) is a dimensionless number that compares the rate of reaction to the rate of diffusion within the pores. The effectiveness factor (η) represents the ratio of the actual reaction rate to the rate if there were no diffusion limitations. These parameters help in quantifying the extent of diffusion limitations and guide the design of more effective catalysts.
