Two bulbs of volume 1 litre each are joined by a 3 cm long and 2 cm diameter tub

Question

Two bulbs of volume 1 litre each are joined by a 3 cm long and 2 cm diameter tube provided with a plug valve. Bulb 1 is filled with pure N2(B) and bulb 2 with N2 containing 5% NH3(A). At time t :0,N2(B) gas with 10% NH3 (A) in it starts flowing through bulb 1 at a rate of 2 litre per hour and the plug valve is simultaneously opened (at t0) to allow diffusion to start. The bulbs are well mixed all the time and diffusion through the connecting tube occurs at pseudo-steady state. The temperature is 25°C and the total pressure is always atmospheric. Diffusivity of NH3 in N2 is 2.3 x 10-5 m2/s (a) Calculate the partial pressure profile of NH3 (A) with time in bulbs 1 [pA1 (t) and 2 [pA2 (t)] (b) When does the flux through the connective tube becomes zero? That is, when the partial pressure of NH3 is equal in the two bulbs [pAi (t)][pA2 (t)] (c) What happens after [pA1 (t)[pA2 (t)]? What are the values of pA1 and pA2 at steady state? Show plots of pA1 and pA2 with time and explain your answer Gas out Q= 2 litres/h d=2cm Bulb 1 (1 litre) P=1atm Bulb 2 (1 litre) P=1atm paz (t) A1 L=3cm Pal (t = 0-0 atm p81 (t 0) 1 atm pm(t = 0) = 0.05 atm pm(t = 0) 0.95 atm 10% NH3 90% N2 Q= 2 litres/h

Explanation / Answer

Its a classic example of two diffusion problems,first is diffusion of 10% ammonia mixture in pure nitrogen and simultaneously diffusion of 5% ammonia in pure nitrogen.

Steady state is defined by equal composition of both Nitrogen and ammonia in both bulbs.

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