I have not seen the post that you have referred so I cannot answer that; but I can give a general idea how I would go about doing it:
1) you have a source (you say it is constant pressure and large) ; you are connecting a smaller tank and pressurizing it; imagine a situation where an (ideal) air compressor is discharging into a cylinder; the compressor is capable of discharging large quantum; so the limitation on filling is the connection resistance; (also remember it is not steady-state, the cylinder is getting filled with differential rate; that is why you are asked to draw a graph against time!)
2) you mentioned the smaller tank is connected by a pipe/tube of known area; you also need to know the (equivalent) length so that you can know the overall resistance to flow in the connection; knowing the pressure difference and the resistance we can calculate flow at any instant
2b) you can have a situation where the resistance is not determining factor; that is choke-flow; look up choke-flow or mach number to understand where such a situation happens; in your problem it would be case initially (hint: as long as the tank pressure is half the source the flow could be choke-flow!)
3) at any instant, given the pressure difference, the flow is determined; you are dealing with a compressible fluid; and the basic equation is known (I presume you know; and remember, this is a steady state equation!)
3a) in your case, where the flow is not constant, the equation is a differential equation and time dependent! if you want a mathematical equation, expressing flow, then a differential equation is to be generated
3b) your exercise is to generate a graph ( 3a above gives the flow rate, which you can convert into volume discharged and hence the pressure of the destination cylinder!)
Since it is a student forum, I am not giving out the answers or a graph; (look at this : http://www.lmnoeng.c...ow/weymouth.htm and also http://www.lmnoeng.com/Gas/choke.htm ) if you still fail to get it, come back, I trust our members may help and guide you to create a simple xl file to generate the graph; !
best wishes
neelakantan
Edited by Neelakantan, 01 May 2014 - 06:39 AM.