Bulk flow of air in a long tube between Antarctica and Australia? I have a 5km diameter clear plastic tube which is open at each end and runs from the center of Antarctica to Lake Eyre in Australia. The tube is on the ground where it can be and at sea level on the ocean.
Will there be bulk flow of the air in the tube? If so, which way will the air flow?
 A: Assuming the tube is insulated along its whole length (which I think is the intent of the question although it's not stated), I think a flow in either direction is stable and sustaining, but there is no particular reason it will form in either direction if the initial conditions are that the air in the tube is still.  It will then depend on the average air temperature in the tube.
You don't need to contrive such a impossible scenario.  Basically, this is asking what happens when a insulated tube is connected between low hot air and high cold air.  This is the same as a chimney in winter.  We all know from experience, that once the air starts rising thru the chimney, it will continue.
However, the reverse direction also works, which is why chimneys have flaps or flue dampers.  Imagine the air in the chimney is still but filled with cold air.  When you let it go, it will flow down into the heated house.  This is flow is stable because the chimney keeps getting refilled with cold air.
A: Natural circulation in tubes is driven by pressure gradient between warmer and colder parts of the fluid. The pressure gradient results from density gradient, which is induced thermally by heating/cooling the tube at different points. However, tube dimensions You've set, make it a very complex problem, probably impossible to solve. Normally models have to be validated with experimental installations as it is difficult to accurately predict what will happen. With such long pipe and complex heat exchange conditions my guess is that the air will flow in all possible directions in different parts of the tube, with average net flow equal to 0.
A: I would think the air in the tube will generally flow from Australia to Antarctica: what we have is actually a "smoke stack": the air is hot in Australia, cold in Antarctica, and the altitude in the center of Antarctica is a couple of kilometers higher than the altitude of Lake Eyre (which is below the sea level).
A: any flow is driven by pressure gradient, which must overcome the friction of flow through the tube. It's a very long way, hence huge pressure drop relative to the initial pressure gradient. No flow
