We agree. A wind chill effect only hastens the approach to the temperature. If the temp were to drop to -40 for a few hours overnight, with no windchill in effect the inanimate object might not reach -40 before the air warms to a balmy -20; with a sufficient windchill it might actually reach -40. So your antifreeze would not have to protect to -60 just because of a -60 windchill, but you might have been able to get away with protecting to -30 had it not been for the wind. Shall we split this hair into 4 strands now ;-)
That experiment also places an insulating layer of air between the "wind" and the food. How about we run the experiment with "wet" and "dry" foods? Or how about foods with a fatty layer on top like pizza?
Wanna run some numbers? Say you blow on your 8 fl.oz. mug of coffee and cool it by 100 degF (like from 200 to 100). That required about 50 BTU to be "liberated" from the liquid. If evaporation was the major source of the cooling, then we'd expect some loss of liquid. At 970 BTU/lb for the heat of vaporization, to lose 50 BTU we'd have to evaporate about 8/10 of an ounce, 10% of the coffee. I'll admit to spoiling the experiment by swigging the coffee before logging the volume in my lab notebook, so you'll perhaps be more careful than I. But I do recall that mugs left to cool from near boiling to room temperature don't lose anywhere near 10% that I recall.
Now take something like a spoonfull of cooked peas or chili beans, track the temperature and loss of water mass as you blow on them. Maybe the exterior will dry out as you blow on them, but the interior will still be juicy moist and there will be a minimum of water loss as a result of the tight fitting difussion barrier represented by the skin of the legume. Now how dry does your cheese pizza get when you blow on it? If "evaporation of water does -much- more to cool the food" then you need to actually have water at the surface to evaporate. How does this work when the water in the pizza is shielded by a thick layer of fat?
Then of course we must consider relative humidity. When you blow on food, you bathe it an a wash of moist air with high relative humidity. Humid air is not conducive to evaporation, as anyone who has tried to use an evaporative "swamp cooler" for central air conditioning in a humid climate can attest.
The effect of evaporation is important but depends on the water content of the food as well as the rate of diffusion of water in the food. Foods with high water content also have a high heat capacity and are thus harder to cool in the first place. Blowing on your hot food works anyway, probably because the food doesn't know about all this ;-)
Forget building anything. Waste money, get this stupid thread over with and do NOT shut your vehicle off at night - just keep it running. But, remove the 4 wheels so it doesn't get driven off :-)
Oh yes, and d> I'm thinking about building something like this. Does anybody have any > suggestions?
An easier solution might be to build a super-insulated garage with an active solar heating system, lots of thermal mass and a backup propane, wood or waste oil furnace. This would keep the entire car, engine and all, warm and toasty (or at least above freezing). An existing garage could be retrofitted with extra insulation and some form of supplemental heating system at the very least.
The advantage of this over a block heater is that when you get thrown out you don't have to resort to sleeping in the dog house.
Seems like the best method is to live somewhere that they don't salt the roads and the snow doesn't fall. I'm sure places like that must exist somewhere. :)
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