Mass Transfer Operations I — Summer 2023

Define: 1) Mass Transfer 2) Equilibrium 3) Mass transfer Co-efficient

Define molecular diffusion. Derive the equation for steady state diffusion of liquid Athrough non diffusing liquid B.

Derive the equation which shows relationship between overall mass transfer coefficients (represented by Kand K ) and individual mass transfer coefficients y x (represented by k and k ) with neat digram. y x

State Fick’s law of diffusion and prove that D = D . AB BA

Explain the concept of penetration theory with neat sketch and suitable assumptions.

Alcohol vapor is being absorbed from a mixture of alcohol vapor and water vapor by means of a nonvolatile solvent in which alcohol is soluble but water is not. The temperature is 97 0C and the total pressure is 760 mm Hg. The alcohol vapor can be considered to be diffusing through a film of alcohol-water-vapor mixture 0.1 mm thick. The mole % of alcohol in the vapor at the outside of the film is 80%, and that on the inside, next to the solvent is 10%. The diffusivity of alcohol-water- vapor mixture at 25 0C and 1 atm is 0.15 cm2/ sec. Calculate the rate of diffusion of alcohol vapor in kg per hour if the area of the film is 10 m2.Moleculer weight of Alcohol = 46 g/mol

At 293 Ksolubility of ammonia in water is given by Henry’s law p=0.3672 C, where p is in atmosphere and Cis in kmol/m2. Amixture of 15 % ammonia and 85 % air by volume at 1 atm is in contact with an aqueous solution containing 0.147 gmol/lit. The air velocity is such that k / k =0.9. Find the concentration of G L ammonia and partial pressure at interface.

Explain the solvent selection criteria for Absorption.

Give stepwise procedure for determining minimum liquid to gas ratio for absorbers.

An air-NH mixture containing 5% NH is being scrubbed with water in a packed33 tower to recover 95% NH . G = 3000 kg/h m2, Ls= 2500 kg/h m2. Tower is maintained31 at 25 0C and 1 atm pressure. Find NTU and height of the tower. The equilibrium relation is given by y*= 0.98x, where x and y are mole fraction units. Ka= 65 kmol/h G m3 atm.

Define any THREE: 1) Tie-line 2) Binodal curve 3) Solutropic solution 4) Plait point

Deduce equation of solvent to feed ratio for single stage liquid-liquid extraction.1

Water- dioxane solution is to be separated by extraction process using benzene as solvent. At 25 0C the equilibrium distribution of dioxane between water and benzene is as follows: Wt % of dioxane in water 5.1 18.9 25.2 Wt % of dioxane in benzene 5.2 22.5 32.0 At these concentrations water and benzene are substantially insoluble. 1000 kg of a 25% dioxane water solution is to be extracted to remove 95% of dioxane. The benzene is dioxane free. Calculate minimum solvent required in kg/ hr if the extraction is done in countercurrent fashion. Estimate the number of stages needed if 1.5 times the minimum amount of solvent is used.

Define: 1) Entrainment 2) Weeping 3) Channeling

With neat sketch discuss Wetted wall column for gas-liquid contact operation.

Calculate the rate of diffusion of acetic acid (A) across a film of non-diffusing water (B) solution 2 mm thick at 170C, when the concentration on the opposite sides of the film are 9% and 3% acid (by weight). The diffusivity of acetic acid in the solution is 0.95*10-9 m2/sec. Density of 9% and 3% by weight acid are 1012 kg/ m3 and 1003 kg/m3 respectively.

Explain the concept of Equilateral –Triangular Coordinates in liquid liquid extraction.

Explain with neat sketch the working mechanism of Ballman Extractor.

Differentiate between tray tower and packed tower.

Mention different types of packing for gas absorption operation and their selection criterion.

Explain Meir’s super saturation theory of crystallization with neat sketch.

Calculate the yield of MgSO *7H Ocrystals when 1000 kg saturated solution of42 MgSO at 353 K (800C) is cooled to 303 K (300C), assuming 10 % of the water is lost4 by evaporation during cooling. Solubility of MgSO at 353 K (800C) = 64.2 kg / 100 kg water4 Solubility of MgSO at 303 K (300C) = 40.8 kg / 100 kg water4 Atomic weight: Mg=24, S=32, O=16, H=1

Give unit of Diffusivity. How to predict the diffusivity in gases?

Explain mass, heat and momentum transfer analogies.

What is leaching? What are the industrial applications of leaching? Discuss the different types of equilibrium diagram for leaching