Wednesday, September 10, 2014

Morning mystery

Why is there condensation on the windshield but not on the side windows? Because the windshield is thicker?


7 comments:

  1. Because the windshield was in direct line of sight of the sun, warming up the glass? The windows are on the sides? They stayed colder/cooler? Maybe?

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  2. because the windshield is pointed at the night sky, which is a huge heat sink. At night, it radiates heat up and loses it faster than the side windows, and so gets comparatively colder. Condensation forms on cold surfaces.

    As an aside, I've heard of people using the heat sucking nature of the clear night skies to make a fridge out of their solar oven, using them in reverse.

    From: http://solarcooking.org/plans/funnel.htm

    "How to Use the Solar Funnel as a Refrigerator/Cooler

    A university student (Jamie Winterton) and I were the first to demonstrate that the BYU Solar Funnel Cooker can be used - at night - as a refrigerator. Here is how this is done.

    The Solar Funnel Cooker is set-up just as you would during sun-light hours, with two exceptions:

    1. The funnel is directed at the dark night sky. It should not "see" any buildings or even trees. (The thermal radiation from walls, trees, or even clouds will diminish the cooling effect.).

    2. It helps to place 2 (two) bags around the jar instead of just one, with air spaces between the bags and between the inner bag and the jar. HDPE and ordinary polyethylene bags work well, since polyethylene is nearly transparent to infrared radiation, allowing it to escape into the "heat sink" of the dark sky.

    During the day, the sun's rays are reflected onto the cooking vessel which becomes hot quickly. At night, heat from the vessel is radiated outward, towards empty space, which is very cold indeed (a "heat sink").

    As a result, the cooking vessel now becomes a small refrigerator. We routinely achieve cooling of about 20º F (10º C) below ambient air temperature using this remarkably simple scheme. "

    Ming

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    Replies
    1. Thanks for the answer. However, one of the rules of storytelling is that factual answers are usually less entertaining than fictional ones. ;)

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    2. eh, takes all kinds! I'm more the compulsive encyclopedia/ mad scientist type personality. :)

      Actually, this makes me wonder if you could travel this way without an electric fridge - cool your stuff down at night with a solar oven rig, then plop the contents in your cooler in the morning, rinse and repeat.

      Ming

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