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DIFFUSIVITIES GAS-LIQUID

Allows for the prediction of gas and liquid diffusivities . The prediction is based upon the group contributions of each individual component of the compound

GASES :

The Diffusivity of gases can be predicted using the Fuller et al equation.

Equation :

Dv = (1.013x10^-7(T^1.75)(1/Mb + 1/Mb)^1/2)/(p[((sum(Via))^1/3 + (sum(Vib))^1/3)]^2)

Dv = diffusivity, m^2/s

T = temperature, K

Ma, Mb = molecular weights of components a and b.

P = total pressure, bar

Sum(Via), Sum(Vib) = Summations of the special diffusion volume coefficients for components a, b. The program calculates these values.

Method of use :

Determine the structure of the gas components. Enter the relevant number of times each component occurs in the structure, ie. if Nitrogen, N, occurs 4 times enter a 4 to the text box next to the N label. Click the Contribution A buttonto determine the contribution of component A. Enter the values to determine the Contribution of component B, (click Contribution B button)

Once the Component contributions have been determined, enter the molecular weights of the components, pressure and temperature of the gas. Calculations are made with each value change, the Diffusivity will be calculated and displayed.

Example :

Methanol in Air

Pressure 1.013 bar

Temperature 25 o C

Element Contribution Number Total

C 16.50 1 16.50

H 1.98 4 7.92

O 5.48 1 5.48

Total contribution of A 29.90

Total contribution of Air , B 20.1

Hence using the equation the Diffusivity of Methanol = 16.2 x 10^-6 m^2/s

LIQUIDS:

Allows for the prediction of liquid heat capacity of a compound at 20 Degrees Celsius . The prediction is based upon the group contributions of each individual component of the compound.

The Diffusivity of Liquids can be predicted using the Wilke and Chang equation.

Equation :

DL = (1.173 x 10^-13(@M)^0.5T)/(uVm^0.6)

DL = Liquid diffusivity, m^2/s

@ = association factor of the solvent

example : 2.6,2.26 for water, 1.9 for methanol, 1.5 for ethanol, 1.0 for unassociated solvents.

M = molecular weight of solvent.

u = viscosity of solvent, mNs/m^2

T = temperature, K.

Vm = molar volume of the solute at its boiling point, m^3/kmol. The program calculates these values.

Method Of Use:

Determine the chemical groups of the compound which the diffusivity needs to be determined for.

Select the contribution value of each group by selecting relevant group structure buttons. I.e. if the compound contains Atomic elements click the Atomic/Molecular button.

Once the button is selected a form will be displayed showing all the structures available. For each structure enter the number of times it appears in the compound, in the associated text box .i.e. if the compounds has two carbon atoms enter a 2 in the associated text box. Click the okay button of each form to enter the contribution value of the structure for the compound.

Once the contribution has been determined enter the viscosity of the component, molecular weight, temperature, and the association factor.

Calculations are made with each value change.

Example :

Predict, diffusivity of phenol in ethanol.

Temperature20 oC

Viscosity of ethanol at 20 o C 1.2 mN s/m^2

Molecular Weight of phenol = 46.

Contribution value :

Atom Volume Number Totals

C 0.0148 6 0.0888

H 0.0037 6 0.0222

O 0.0074 1 0.0074

Ring -0.015 1 -0.015

0.103 m^3/Kmol

Hence using the equation the Diffusivity = 8 x 10^-10 m^2/s