Mass Transfer Questions and Answers – Diffusion through Variable Area

This set of Mass Transfer Multiple Choice Questions & Answers (MCQs) focuses on “Diffusion through Variable Area”.

1. Consider steady-state equimolar counterdiffusion through the converging-diverging tube. Given: r1=1cm; r2=2cm; NA=10-6 kmol/m2.s at the vessel 1 end of the tube. The rate of transport of B at the vessel 2 end of the tube is
a) 2*10-6 kmol/s, towards vessel 1
b) 2.5*-7 kmol/s, towards vessel 1
c) 5*10-6 kmol/s, towards vessel 2
d) 9*10-7 kmol/s, towards vessel 2
View Answer

Answer: b
Explanation: None.

2. Two large vessels containing gaseous mixture of A and B at different concentrations but at the same total pressure are connected by a tapered tube of length 15cm and end diameters 1cm and 4 cm. what should be the diameter of a cylindrical tube of the same length that allows the same rate of transport of A?
a) 2.5 cm
b) 2 cm
c) 3cm
d) 3.5 cm
View Answer

Answer: b
Explanation: None.

3. In a tapered tube connecting two vessels with a gaseous mixture at different concentrations but the same total pressure, where will the magnitude of the flux be maximum along the length of the tube, considering the tube has a variable cross-sectional area?
a) At the larger diameter end
b) At the smaller diameter end
c) Midway in the tube
d) Somewhere in between the midway and the larger diameter end
View Answer

Answer: b
Explanation: None.
advertisement

4. Equimolar counterdiffusion of A and B occurs through a spherical film of i.d=ri and thickness δ. The flux of A is NA1 at r=ri. The flux through a flat film of the same thickness is NA2. if NA1 is larger than NA2 by 5%, the film thickness δ is
a) 0.025ri
b) 0.05ri
c) 0.1ri
d) 0.01ri
View Answer

Answer: b
Explanation: None.

5. A napthelene hemisphere is placed on a glass plate and a napthelene ball of identical diameter is kept suspended in the stagnant air in two large rooms. The respective shapes of the ball are maintained while they sublime and reduce in size. Which of the following statements are true in this connection?
a) They take the same time for complete sublimation
b) The sphere disappears first
c) The hemisphere disappears first
d) Nothing definite can be said
View Answer

Answer: a
Explanation: None.
Free 30-Day Java Certification Bootcamp is Live. Join Now!

6. Sublimation of a long cylinder made of napthelene occurs in a large volume of stagnant air. The time required for its complete sublimation is
a) infinite
b) half the time of sublimation of a sphere of the same mass
c) twice the time of sublimation of a cylinder of the same mass and lengthy/diameter=1
d) half the time of sublimation of a cylinder of the same mass and lengthy/diameter=1
View Answer

Answer: a
Explanation: None.

7. A tapered tube of length 8cm and end diameters 2cm and 4cm connects two vessels containing mixtures of A and B. if the tapered tube is replaced with a cylindrical tube of diameter 6cm, what will be the required length of the cylindrical tube to maintain the same flow rate as in the previous case?
a) 8cm
b) 16cm
c) 36cm
d) 48cm
View Answer

Answer: c
Explanation: – (Area)*(flux) =Constant=W
W1 for cylinder= (πr2 DAB(P1-P2))/RTL
W2 for tapered tube = (πDAB*r1*r2(P1-P2))/RTL
Equate W1 and W2.

8. In a binary gas mixture containing A and B, If NA=-2NB, what will be the expression for NA?
a) 2(D*(P1-P2))/RTL
b) (D*(P1-P2))/RTL
c) DP*(2RTZ)-1*ln[(P-P1)/(P-P2)].
d) 2DP*(RTZ)-1*ln⁡[(P-P1)/(P-P2)].
View Answer

Answer: a
Explanation: NA= (NA+N)CA/C – DABdCA/dz
NA=(NA/2)PA/P – DAB(dPA/dz) /RT
NA(1-2PA/P) = – DAB(dPA/dz)/RT
Integrate on both sides.

Sanfoundry Global Education & Learning Series – Mass Transfer.

advertisement

To practice all areas of Mass Transfer, here is complete set of 1000+ Multiple Choice Questions and Answers.

advertisement
advertisement
Subscribe to our Newsletters (Subject-wise). Participate in the Sanfoundry Certification contest to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!

Youtube | Telegram | LinkedIn | Instagram | Facebook | Twitter | Pinterest
Manish Bhojasia - Founder & CTO at Sanfoundry
I’m Manish - Founder and CTO at Sanfoundry. I’ve been working in tech for over 25 years, with deep focus on Linux kernel, SAN technologies, Advanced C, Full Stack and Scalable website designs.

You can connect with me on LinkedIn, watch my Youtube Masterclasses, or join my Telegram tech discussions.

If you’re in your 40s–60s and exploring new directions in your career, I also offer mentoring. Learn more here.