Mass Transfer

Penetration theory states that the mass transfer co-coefficient is equal to (where, De is diffusivity and 't' is time)
A. (De.t)1/2
B. (De/t)1/2
C. (4Det)1/2
D. (4De/t)


The velocity, concentration and temperature boundary, for the boundary layer development on a flat plate during connective mass transfer will be same, if

A. NSc = 1
B. NSc = NPr = NLe
C. NPr = NLe
D. NSc = NLe


Penetration theory relates the average mass transfer co-efficient (K) with diffusivity (D) as

A. K `alpha` D
B. K`alpha``sqrt(D)`
C. K`alpha`D1.5
D. K`alpha`D2

Pick out the wrong statement.
A. The binary diffusivity in liquids is of the order of 10-5 cm2 /sec.
B. Molecular diffusion in solid is much faster than that in liquids.
C. Particles movement from higher concentration to lower concentration takes place in diffusion process.
D. According to Poiseuille's law, the permeability decreases with increase in temperature for flow of a gas through a given capillary.

  A solid is being dried in the linear drying rate regime from moisture content Xo to XF. The drying rate is zero at X = 0 and the critical moisture content is the same as the initial moisture Xo. The drying time for M = (Ls/ARc) is (where, L = total mass of dry solid, A = total surface area for drying Rc = Constant maximum drying rate per unit area X = moisture content (in mass of water/mass of dry solids))
A. M(Xo - XF)
B. M(Xo/XF)
C. M ln(Xo/XF)
D. MXo ln(Xo/XF)