|Yesterday, I was surprised to be considered strange for not putting hot liquids that I want cooled into the fridge, instead cooling them to room temperature first. If I did polls I would now poll whether you people do that or not, but I don't, so I won't. What I'll do instead is provide SCIENCE!|
For simplicity's sake, let's say you have one litre of water at 50°C, room temperature is 25°C and your fridge's target temperature is 0°C (but not frozen). Your fridge has a generous one third of a cubic metre capacity (slightly larger than an average fridge I think).
The specific heat of water is about 4.186 kJ per litre per °C. So if you put your litre into the fridge at 50°C instead of at 25°C, you're putting 4.186*(50-25) kJ of unnecessary energy into your fridge that will need to be dissipated. That's 104.65kJ.
The specific heat of air is an imprecise thing depending on pressure, humidity and temperature, but a decent approximation is 1kJ/kg °C. One kilogram of air is also approximately one cubic metre, conveniently three times the volume of our hypothetical fridge. So, it takes about a third of a kilojoule to raise the temperature of an entire fridgeful of air by one degree. Which means our 104.65kJ of unnecessary warmth in our single litre of water is the energy equivalent to raising the temperature of a fridgeful of air from 0°C to 314°C.
Alternatively, and more realistically, it's the equivalent of letting all the cold air out of the fridge, to be replaced with room-temperature air, more than twelve times. People are mostly reluctant to leave the fridge door open because it will let a fraction of a fridgeful of cold air out - by comparison you can see that letting out a bit of cold air is nothing compared to introducing heat unnecessarily. Especially since your fridge's target temperature isn't even really that low - all simplified figures are simplified to understate the comparison.
And that's just one litre, at a not-very-hot 50°C. I had five litres of lemon barley water, at probably closer to 70°C - if I put that in the fridge without cooling, that would be the wasted energy equivalent of heating a fridgeful of air to a fantastic 2825°C. That's over 5000 fahrenheit, for Americans.
SCIENCE! [14:18] [12 comments]