Wednesday, August 16, 2006

New job, less postings

I'm now working at Google. Specifically, I'm working on Google Earth. The project is irresistably cool, I work with interesting and talented people, I'm learning a lot, and there is plenty of money and resources to get the job done. I'm pretty happy about the whole thing.

But my posting should be about techie stuff. So, along that vein, I'm sure you are all wondering, does water evaporate from the pool faster or slower on cooler nights? I think I have a counterintuitive answer: cold air speeds evaporation.

The pool water holds vastly more heat than the air above it, so the air in contact with the water will be at the water temperature, pretty much regardless of the ambient temperature. Lower ambient temperatures usually come with lower dew points, which means that once the air has been heated to the pool temp, initially colder air is dryer. More water can evaporate into this colder air.

There is a second effect as well. On a windless night, the convection over the pool is driven by the temperature difference between the pool and the ambient air. As ambient gets colder, the convection gets faster and more dry air is brought to the pool surface, evaporating more water.

The net result is that on a cool night, the area all around the pool gets quite damp. I'm fairly sure this is pool water recondensing out of the air as the air moves away from the pool and cools back down.

1 comment:

  1. Congrats and good luck, Iain! Google Earth is the coolest project. Maybe you'll get to work a little on Google Moon and Google Mars.

    Dan Schmelzer