Diffusion & Convection_Part 1

Consider loss of ethanol vapor by diffusion from a half-filled open test tube. At what point in the diffusion path will the contribution of the bulk flow term to the molar flux be maximum? (Allocation time: 2 min)

• At the liquid-gas interface

• In the bulk liquid

• In the bulk gas

A sheet of Fe 1.0 mm thick is exposed to an oxidizing gas on one side and a deoxidizing gas on the other at 725°C. After reaching steady state, the Fe membrane is exposed to room temperature, and the C concentrations at each side of the membrane are 0.012 and 0.075 wt%. Calculate the diffusion coefficient (m²/s) of C if the diffusion flux is 1.4×10^-8 kg/m².s. (Allocation time: 15 min)

• 9.87x10^-12

• 9.87x10^-13

• 9.87x10^-11

• 9.87x10^-10

In industries titanium is hardened through diffusion of carbon. The concentration of carbon at 1 mm into the surface of the titanium slab is 0.25 kg/m³ and at 3 mm the concentration is 0.68 kg/m³. The rate at which the carbon is entering into its surface is 1.27x10^-9 kg/m².s. Calculate the value of diffusion coefficient (m²/s) of carbon. (Allocation time: 15 min)

• 5.91x*10^-12

• 5.91x10^-10

• 5.91x10^-11

• 5.91x10^-13

Define the convective mass transfer. (Allocation time: 3 min)

• The transport of material between a boundary surface and a moving fluid

• The transport of material between two immiscible moving fluids separated by a mobile interface.

What are the factors affecting k_c? (Allocation time: 5 min)

• The properties of the fluid

• The dynamic characteristics of the flowing fluid

• The geometry of the specific system of interest

A value of k_G was experimentally determined to be 1.465 x 10^-3 kgmol/s.m².atm for A diffusing through stagnant B. Given system's conditions are as follows: the partial pressure are p_A1= 0.20 atm, p_A2=0.05 atm and total pressure, P_t=1.0 atm. For the same flow and concentrations, predict the k'_G for equimolar counterdiffusion. (Allocation time:15 min)

• 1.279 x 10^-3 kgmol/s.m².atm

• 1.279 x 10^-4 kgmol/s.m².atm

• 1.279 x 10^-5 kgmol/s.m².atm

• 1.279 x 10^-6 kgmol/s.m².atm

A value of k'_G was experimentally determined to be 1.279 x 10^-3 kgmol/s.m².atm for A diffusing through stagnant B. Given system's conditions are as follows: the partial pressure are p_A1= 0.20 atm, p_A2=0.05 atm and total pressure, P_t=1.0 atm. For the same flow and concentrations, calculate the flux of A for equimolar counterdiffusion. (Allocation time:15 min)

• 19.2 kgmol/s.m²

• 0.192 kgmol/s.m²

• 1.92 kgmol/s.m²