HW 1 - p 3.15 - Diffusivity & Mass Transfer of Isopropanol in H2O(l) and N2(g) - 6 pts
Isopropyl alcohol is undergoing mass transfer at 35 oC and 2 atm under dilute conditions through water, across a phase boundary, then through nitrogen. Based on the data given below estimate for isopropyl alcohol:
(a) The diffusivity in water using the Wilke-Chang equation
(b) The diffusivity in nitrogen using the Fuller et al. equation
(c) The product, DAB ρM, in water
(d) The product, DAB ρM, in air
Where ρM is the molar density of the mixture
Using the above results, compare:
(e) The diffusivities in parts (a) and (b)
(f) The diffusivity-molar density products in Parts (c) and (d)
Lastly:
(g) What conclusions can you come to about molecular diffusion in the liquid phase versus the gaseous phase?
Data:
Component Tc,oR Pc, psia Zc VL, cm^3/mol
Nitrogen 227.3 492.9 0.289 -
Isopropyl alcohol 915 691 0.249 76.5
(a) The diffusivity in water using the Wilke-Chang equation
(b) The diffusivity in nitrogen using the Fuller et al. equation
(c) The product, DAB ρM, in water
(d) The product, DAB ρM, in air
Where ρM is the molar density of the mixture
Using the above results, compare:
(e) The diffusivities in parts (a) and (b)
(f) The diffusivity-molar density products in Parts (c) and (d)
Lastly:
(g) What conclusions can you come to about molecular diffusion in the liquid phase versus the gaseous phase?
Data:
Component Tc,oR Pc, psia Zc VL, cm^3/mol
Nitrogen 227.3 492.9 0.289 -
Isopropyl alcohol 915 691 0.249 76.5
posted by Dr. B at 2:10 PM
3 Comments:
The liquid solution is dilute, so the density is the same as that of the solvent...water. density = 1000 g/cm^3. The MW of the solution is also the same as that of water.
In the gas phase, use PV=nRT.
what is the significance of the diffusivity-molar density value? is this the term that determines rate of mass transfer, not simply diffusivity alone?
Karen 4:00 PM
That is a REALLY good question.
If you take a closer look at the molar density, you will notice that it is just another name for total molar concentration. The units are moles per volume. So, here you are really just calculating Ctot DAB. This is not that special, but it does take into account how EACH term ( Ctot and DAB ) change in response to changes in response to composition. Parts (f) & (g) tie things together here. How are the diffusive fluxes of IPA in water and alcohol related given the same concentration gradient ? Is one diffusive flux vastly greater thanthe other or not ? Why or why not ?
Post a Comment
<< Home