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.

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.

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