# Mass Transfer GATE-2015

**Q 1.** For a binary mixture of components, A and B, N_{A} and N_{B} denote the total molar fluxes of components A and B, respectively. J_{A} and J_{B} are corresponding molar diffusive fluxes. Which of the following is true for equimolar counter-diffusion in the binary mixture?

**Q 2.** Benzene is removed from air by absorbing it in a non-volatile wash-oil at 100 kPa in a counter-current gas absorber. Gas flow rate is 100 mol/min, which includes 2 mol/min of benzene. The flow rate of wash-oil is 50 mol/min. Vapor pressure of benzene at the column conditions is 50 kPa. Benzene forms an ideal solution with the wash-oil and the column is operating at steady state. Gas phase can be assumed to follow ideal gas law. Neglect the change in molar flow rates of liquid and gas phases inside the column. For this process, the value of the absorption factor (up to two decimal places) is ___________.

**Q 3.** A spherical naphthalene ball of 2 mm in diameter is subliming very slowly in stagnant air at 25^{o }C. The change in the size of the ball during the sublimation can be neglected. The diffusivity of naphthalene in air at 25^{o} C is 1.1×10^{-6} m^{2}/s. The value of the mass transfer coefficient is B×10^{-3} m/s, where B (up to one decimal place) is _________________.

**Q 4.** Identify the WRONG statement amongst the following:

**Q 5.** A multi-stage, counter-current liquid-liquid extractor is used to separate solute C from a binary mixture (F) of A and C using solvent B. Pure solvent B is recovered from the raffinate R by distillation, as shown the schematic diagram below.

Locations of different mixtures for this process are indicated on the triangular diagram below. P is the solvent-free raffinate, E is the extract, F is the feed and Δ is the difference point from which the mass balance lines originate. The line PB intersects the binodal curve at U and T. The lines PΔ and FB intersect the binodal at V and W respectively.

The raffinate coming out of the extractor is represented in the diagram by the point:

**Q 6.** A binary feed consisting of 25 mol% liquid and 75% vapor is separated in a staged distillation column. The mole fraction of the more volatile component in the distillate product is 0.95. The molar flow rate of distillate is 50% of the feed flow rate and the McCabe-Thiele method can be used to analyze the column. The q-line intersects the operating line of the enriching section at (0.35, 0.5) on the x-y diagram. The slope of the stripping section operating line (up to one decimal place) is ______________.

**Q 7.** Consider a steady mass transfer process between well-mixed liquid and vapor phases of a binary mixture comprising of components A and B. The mole fractions of component A in the bulk liquid (x_{A}) and bulk vapor (y_{A}*) *phases are 0.36 and 0.16, respectively. The mass transfer coefficients for component A in liquid and vapor phases are 0.1 mol/(m^{2}.s) and 0.05 mol/(m^{2}.s), respectively. The vapor-liquid equilibrium can be approximated as y_{A}^{*} = 2x_{A}, for x_{A} less than 0.4. The mole fraction of A in the liquid at the interface (up to two decimal places) is ___________.

**Q 8.** Adsorption on activated carbon is to be used for reducing phenol concentration in wastewater from 0.04 mol/L to 0.008 mol/L. The adsorption isotherm at the operating temperature can be expressed as *q* = 0.025C^{1/3}: where *q* is the phenol concentration in solid (mol/g solid) and C is the phenol concentration in water (mol/L). The minimum amount of solid (in grams) required per liter of wastewater (up to one decimal place) is _____________.