Question

What will be the value of mass average velocity (m/s)?

(a) 0.981

(b) 0.891

(c) 0.985

(d) 0.857

I have been asked this question in examination.

My query is from Concentration and Velocity topic in section Modes and Diffusion of Mass Transfer

Answer 1

Correct choice is (a) 0.981

The best I can explain: Mass average velocity= (ρ1u1+ρ2u2)/ ρ

                 ρ1= (p1*M1)/RT

                   ρ= (p*M)/RT.

                 Dividing these two equations

              ρ1/ ρ = (p1*M1)/pM =(y1*M1)/M

              M=y1*M1+y2*M2=0.79*28+0.21*32=28.84

              Mass average velocity= (y1*M1*u1+y2*M2*u2)/M

                                   = (0.21*32*0.04+0.79*0.035)/28.84

                                   = 0.981.