Mass Transfer Problem question

[joe98]

Consider a chemical species A, which is soluble in water. The equilibrium of this system with A in air is described by the following question:

C(air) = HC(water)

where C(air) is mass concentration of the species in air
C(water) is the mass concentration in water, and the Henrys Law constant is H=0.00070(dimensionless)

the film mass transfer coefficient for the air side is 0.07m/s, and the water side is 8x10^-6 m/s

Answer the following, assuming the air stream contains 10 mol% of A at 100KPa and the aqueous solution contains 5 mass% of A at 25C...and use 17g/mol for molar mass of the speciesA) What is the mass driving force for the mass transfer, in mass concentration units, viewed from the gas phse?

I used C=PM/RT=100000*0.017/8.314*(273+25)=0.069 kg/m^3
What is the mass transfer rate( express as mass flux)?

Here i use
N=KC

where K=1/k + H/k2=5.33*10^-3 m/sCould someone assist me in this question...Any suggestions

 

[joe98]

Any suggestions guys on calculating the mass transfer driving force?

 

[joe98]

Heyguys, could you have a look if i am on the right track

Heres my working out to calculate the driving force in mass concentration units from the gas phase

I converted 10 mol% to 0.17 mass%, (which is in mole fraction)

then i calculated the partial pressures of inlet and outlet

PP(waterinlet)=100*10^3* 0=0
PP(gas inlet)= 100*10^3 * 0.005=5000Pa

Mass fraction(water)=0.05*0.0007=3.5*10^-5

Therefore , PP(water out) = 3.5*10^-5 * 100*10*3 = 3.5 Pa

Mass fraction (air) = 1.7*10^-3 * 0.0007=1.19*10^-6

therefore, PP(air out) = 1.19*10^-6 * 100*10^3 = 0.119 Pa

then i calculated C(lmcd) = (5000-3.5) - (0.119-0))/ln(5000-3.5)/0.119 =469 PaTherefore i used C=PM/RT = 469*0.017/8.314*298=3.22*10^-3 Kg/m^3Is this correct guys

 

[Chestermiller]

Heyguys, could you have a look if i am on the right track

Heres my working out to calculate the driving force in mass concentration units from the gas phase

I converted 10 mol% to 0.17 mass%, (which is in mole fraction)

then i calculated the partial pressures of inlet and outlet

PP(waterinlet)=100*10^3* 0=0
PP(gas inlet)= 100*10^3 * 0.005=5000Pa

Mass fraction(water)=0.05*0.0007=3.5*10^-5

Therefore , PP(water out) = 3.5*10^-5 * 100*10*3 = 3.5 Pa

Mass fraction (air) = 1.7*10^-3 * 0.0007=1.19*10^-6

therefore, PP(air out) = 1.19*10^-6 * 100*10^3 = 0.119 Pa

then i calculated C(lmcd) = (5000-3.5) - (0.119-0))/ln(5000-3.5)/0.119 =469 Pa


Therefore i used C=PM/RT = 469*0.017/8.314*298=3.22*10^-3 Kg/m^3


Is this correct guys

Getting the driving force:

1. calculate the concentration of the species in the bulk gas phase, using concentration units for the gas phase

2. calculate the concentration of the species in the bulk liquid phase, using concentration units for the liquid phase

3. take the result in step 2 and multiply by the Henry's Law constant to get the gas phase concentration that would be in equilibrium with the species concentration in the liquid phase

4. subtract the result from step 3 from the result for step 1. This is the mass transfer driving force for species flux from the gas phase to the liquid phase. The mass transfer driving force for species flux from the liquid phase to the gas phase is minus this value.

 

[alphy]

would be appreciated

Sure, I can assist you with this question. Let's break down the problem and go through it step by step.

First, we need to calculate the mass driving force for the mass transfer in the gas phase. This can be done using the equation C=PM/RT, where C is the concentration in kg/m^3, P is the pressure in Pa, M is the molar mass in kg/mol, R is the gas constant (8.314 J/mol*K), and T is the temperature in K. Using the given values, we get:

C = (100000 Pa)(0.017 kg/mol)/(8.314 J/mol*K)(298 K) = 0.069 kg/m^3

This is the concentration of species A in the gas phase at the given conditions.

Next, we need to calculate the mass transfer rate, expressed as a mass flux. This can be done using the equation N=KC, where N is the mass flux in kg/m^2*s, K is the mass transfer coefficient in m/s, and C is the concentration in kg/m^3. The mass transfer coefficient, K, can be calculated using the given film mass transfer coefficients for the air and water sides:

K = 1/k + H/k2 = (1/0.07 m/s) + (0.00070 dimensionless/8x10^-6 m/s) = 5.33x10^-3 m/s

Now, we can plug in our values to calculate the mass flux:

N = (5.33x10^-3 m/s)(0.069 kg/m^3) = 3.68x10^-4 kg/m^2*s

This is the mass transfer rate, expressed as a mass flux, for species A at the given conditions.

I hope this helps! Let me know if you have any further questions.