14. For flow of a binary gas mixture over a flat plate, boundary layers of velocity and concentration develop. Which of the following statements concerning the thicknesses of the velocity (δ) and concentration boundary layers is true?
(A)
(B)
(C)
(D) none of the above

10. Wearing the face mask can provide a critical barrier, reducing most infectious viruses during coughing, especially of asymptomatic people and those with mild symptoms of COVID-19. Please calculate the force of cough flow acting on the mask. Assume the mask perfectly covers the mouth. The velocity of cough flow is 10 m/s and the opening of the mouth is 1 cm in diameter. (A)0.001 N (B) 0.01 N (C) 0.1 N (D)1N (E) 10 N

11. What is the SI unit of mass flux? (A) Kg/s, (B) g((s/ cm2), (C) Kg(s /m2), (D) g/s

12. Concerning the SI units of kinematic viscosity, thermal diffusivity, and mass diffusivity, which of the following statements is true? (A) All three are different. (B) All three are the same as m2/s. (C) All three are the same as s/m2. (D) All three are the same as s/cm2.

13. For the following mixtures, (a) H2-Oz at 1 atm and 273 K, (b) N2-O2 at I atm and 273 K, (c) dilute aqucous ethanol solution at 298 K, and (d) Cd in Cu at 293 K, place them in the order of increasing mass diffusivity. (A) (a)(b)(c)(d), (B) (c)(d)(a)(b), (C) (d)(c)(a)(b), (D) (d)(c)(b)(a)

15. Consider a spherical particle A of radius R dissolving in a stagnant liquid B. Once dissolved, A and B react to form C with an irreversible first-order reaction reaction rate constant k). The solubility of A in B, CAo, is small and the system can be approximated as a dilute binary system. The diffusivity of A in B is DAB. The system can be treated as in a pseudo-steady state. Let b2 denote (k,R/DAB). What is the molar flux of A at the particle surface? (A) (B) (C) (D)

16. Continued from the above problem, what is dmaldr? (-molecular weight of A, ma-mass of particle (A) (B) (C) (D)

複選題17. Consider the absorption of gas A by a laminar falling film of liquid B. Gas A is onlyslightly soluble in B, and the diffusion takes place so slowly in the liquid film that Awill not penetrate very far into B. The concentration of A at the interface is maintainedat CAo and the maximum velocity of the fluid is Vmar. Let x be the coordinate into theliquid film, z the coordinate down the liquid film, and DAB the mass diffusivity of A inB. The molar concentration of A, CA, is a function of x and z. Which of the followingstatements is true?(A) CA increases with increasing x.(B) CA decreases with increasing z.(C) CA increases with decreasing at fixed x and z.(D) CA decreases with increasing at fixed x and z.

18. Continued from the above problem, what is the molar absorption rate of A at the gas/iquid interface? Here, W and L are the width and length of the liquid film exposed to gas A. (A) (B) (C) (D)

19. The equation of continuity of A in a dilute binary solution can be written asHere, is the mass average velocity and is the molar reaction rate of A. For thesituation of pure diffusion in solids, what will the above equation be reduced to?(A) (B)(C)(D)

複選題20. Which of the following statements is true? (A) Eddy diffusivity is a physical property of a fluid. (B) Eddy diffusivity depends on turbulent intensity of the flow. (C) Nusselt number of heat transfer is analogous to Schmidt number of mass transfer. (D) Chilton-Colburn analogy applies to laminar tube flow.