Sunday, April 18, 2010

Fountain engineering


Early this afternoon I took a long walk to the library and stopped to admire this carefully regulated array of fountains. What grace and order! A Roman emperor would have been proud to put such fountains in his Imperial villa on the Isle of Capri.

As I gazed upon the fountains, my engineering interest quickly elbowed aside my aesthetic interest. How were these increasing fountain heights engineered?

I surmised that, for the sake of economy, all of the fountains were fed by a single submersible pump located right below the pond surface. The maximum height of each fountain would be predominantly determined by the flow resistance, expressed as pressure drop, across each fountain's nozzle. (Specific piping resistance to the water flow would slightly reduce fountain height.) For a given flow rate, a nozzle giving the smallest pressure drop would output the lowest water velocity, resulting in the lowest fountain height. This is not just my opinion. Daniel Bernoulli described how water flow is affected by changes in pressure and height back in 1738.

Therefore, if you want progressively higher fountain heights, you would need progressively more restrictive nozzles. A few piping tweaks here or there would be sufficient for fine tuning.

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