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Comment by Leo_Germond | Hacker News Reader

Well for one submarines have parts that are over water, and can be stored in dry bays on the continent, for repair or construction (also the steel itself is stored on the continent prior to being used). For second the coldest wind chill recorded in the US was -100°F at McGrath, Alaska in 1989. So it's not too much of a stretch to take this value a minimal value for testing the material.

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McGrath, AK is at 330ft of elevation in a river basin surrounded by mountains, 170mi from it's nearest shoreline (as the bird flies). Air temperatures at sea level never reach the extremes of coldest air temperatures on Earth, which are always at elevation. This is somewhat due to air temperature being a function of air pressure (the denser the air, the warmer it gets), and air pressure is greatest at sea level. But it is largely due to the freezing temperature of sea water, and that the warmest water will be at the surface due to convection. Warm water rises to the surface, and the coldest water temperatures are at the deepest bottom of the ocean, and never colder than the freezing temperature of sea water.

Wind chill temperatures only affect humans (and other living things). Materials cannot fail below the true temperature of the environment.

That is not true. We don’t necessarily call it wind chill, but evaporative cooling certainly can decrease the temperature of non-living things below the temperature of the atmosphere.

Wind chill only increases the rate of cooling, not the absolute value.

Evaporative cooling by definition cannot cool below the wet-bulb temperature.

But wet bulb temperature != true temperature of the environment, no?

> Wind chill only increases the rate of cooling, not the absolute value.

Right. The absolute value is related to the evaporation process, which is affected by wind.

> Evaporative cooling by definition cannot cool below the wet-bulb temperature.

Wet bulb temperature is not “the true temperature of the environment”. Besides, that is true for humans as well, so again not any different between living and non-living things.

The main point is that a thing left in a given environment can end up at temperatures lower than that of their local environment. This process depends on the atmosphere in contact with the thing, which depends on winds.

We're dealing with two misconceptions here. Wind chill is not affected by evaporative cooling. You can of course go below ambient with evaporative cooling, or air conditioning, or any number of methods.

Wind chill is explicitly and only the experienced subjective temperature caused by cold air being continuously replaced by the wind.

For example, take the US National Weather Service's wind chill formula, which only uses wind speed and tempurature as inputs and provides the wind chill in W/m².

Source: https://www.weather.gov/media/epz/wxcalc/windChill.pdf

> Wet bulb temperature is not “the true temperature of the environment”. Besides, that is true for humans as well, so again not any different between living and non-living things.

Wind chill and evaporative cooling are independent mechanisms, and the wind chill value and wet bulb temperature are separate values.

My reply was to your original comment, which said:

> For second the coldest wind chill recorded in the US was -100°F at McGrath, Alaska in 1989.

That value is not the temperature that an object could have reach at that time and place. It is the wind chill, an approximation of how cold it would have to have been on a windless day to make a person subjectively feel equally cold.

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