Homework No. 2 (Unit 2) 1. A droplet of liquid A, of radius r1, is suspended in a stream of gas B. Assume that there is a spherical stagnant gas film of radius r2 surrounding the droplet. The concentration of A in the gas phase is xA1 at r=r1, and xA2 at the outer edge of the film, r=r2. (a) By a shell balance, show that for steady-state diffusion r2NAr is a constant within the gas film, and set the constant equal to r12NArl, the value at the droplet surface. (b) Show that the equation r12NAr1=1xAcDABr2drdxA (c ) Integrate this equation between the limits r1 and r2 to get NAr1=r2r1cDAB(r1r2)ln(xB1xB2) What is the limit of this expression when r2