9

Flow through chains of tanks

Five relatively narrow tanks are connected at their bottoms by hoses. The first is tank filled to a high level, the second and all the others are basically empty at start. When the pipes are opened, water begins to flow from left to right (Figure 1), and the levels change as seen in the graph.

Interpretation

For water to flow from tank to tank, there must be appropriate pressure differences across the pipes. High pressure differences let the levels in neighboring tanks change fast. Since the tanks on the right have the same initial levels, their levels do not rise initially. It takes a while for them to rise as well. All the levels tend to equilibrate. Toward the end, the flows have become small and the processes run slowly.

This is an example of a substance travelling through storage elements as it occurs in diffusion (see Chapter 4).