• scissors
    January 9th, 2013ImogenUncategorized

    Hello science fans. Now that I have graduated University and become a Real Person With a Job and Everything, I have become best friends with my hot water bottle. To the extent I mention it so often in texts that it has become abbreviated to HWB. There is, I am discovering, an art to filling a hot water bottle so that it provides enough heat for enough time without being too unbearably hot.

    The problem is, I always get distracted and don’t stop the kettle before it boils. Boiling water makes for an HWB that’s too hot under the duvet. But when I add cold water to the near-boiling water, this just feels a bit wrong. Basically, I lied when I said this is an art. It’s not, it’s a science, and here’s why.

    Let’s say that instead of water in my container, I have identical rocks. Each rock has a hotness score or 0-10 where 0 is room temperature (the temperature all rocks are going to cool to eventually) and 10 is super duper hot. A group of rocks collectively loses one hotness point per minute as it cools. Par example…

    Scenario 1: I use 10 rocks each of hotness 1 so my container is at temperature 1. I have 10 hotness points and this keeps me warm for 10 minutes. Hmm not good enough.

    Scenario 2: I use 5 rocks each of hotness 10.. This gives me a total of 5×10=50 hotness points so my container keeps me hot for 50 minutes. A container which starts at hotness 10 is too warm though

    Scenario 3: As a compromise, I use 10 rocks of hotness 5. This equals the same amount of hotness points as before, so keeps me warm for the same amount of time as Scenario 2 but the starting average temperature of 5 is perfect!

    Scenario 4: I’m so pleased with my success from Scenario 3 that I forget the rest of my rocks are on the fire and I come back to find they are now all 10 hotness points. Oh no! Too hot! What to do? I need 50 hotness points and a starting temperature of 5 for optimum bed cosiness. If I take 5 rocks of hotness 10 from the fire and add 5 rocks of 0 hotness (room temperature) then the average (overall) temperature is now (10+10+0+0)/4=5 hotness, and I have 50

    hotness points to keep me warm for ages! Hooray!

    This means that if I use near-boiling water and then add cold, it will give me a hot water bottle which is not too hot, which will last for longer!

    You are welcome.


    Not 42, just HWB
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