Explain: (i) mass average velocity, (ii) molar average velocity, (iii) mass diffusion velocity, and (iv) molar diffusion velocity. Using the analogy of thermal and diffusion resistance, write the...

Explain: (i) mass average velocity, (ii) molar average velocity, (iii) mass diffusion velocity, and (iv) molar diffusion velocity.

Using the analogy of thermal and diffusion resistance, write the expression for the diffusion rate for cylinder and sphere.