When Boiling is Freezing, Perceived & Relative!

(From an old time served refrigeration engineers point of view)

With this year’s heatwaves, how many times have you heard people say, “It’s too hot” or “It’s boiling outside”?

Completely inaccurate, of course, but we all know what they mean!

Our body temperature is around 37°C, so anything approaching that temperature can certainly feel warm or hot. Anything considerably below it might feel cold. We generally prefer an environment of around 22°C when relaxing and watching TV, perhaps less when exercising and sometimes more as we get older. Of course, personal preferences vary!

But what exactly is boiling?

Ask almost anyone and they’ll probably say it’s what happens when you boil a kettle. At normal atmospheric pressure, water boils at 100°C and, as it boils, changes from a liquid into vapour.

Ask them what freezing is and the answers might be a little more varied. My wife might say anything below 18°C! But generally, we’re talking about the same chemical, water, which freezes at 0°C under normal atmospheric pressure to form ice.

Now let’s move on to other chemicals, less familiar to most people and not normally associated with everyday conversations: refrigerants.

These have similar properties to water, but their boiling and freezing temperatures can be very different.

Let’s take one of the most popular air-conditioning refrigerants, R32.

R32 is a single-component refrigerant with a boiling point of approximately -52°C at atmospheric pressure. Its freezing point is around -136°C.

That means, at atmospheric pressure, R32 can boil at a temperature that most of us would associate with extreme cold rather than heat!

Of course, refrigerant boiling temperatures change with pressure, which is fundamental to how refrigeration and air conditioning systems work.

As the liquid refrigerant evaporates, it absorbs heat from its surroundings. This is precisely what allows an air-conditioning system to remove heat from the air inside a building.

Through personal experience (and perhaps some careless handling in years gone by!), I can assure you that when refrigerant boils, it certainly isn’t hot! 

A cold burn is as dangerous and as painful as a hot burn, be careful!

So there we have it. Boiling doesn’t necessarily mean hot, just as freezing doesn’t necessarily mean the same temperature for every substance.

It’s all relative. It depends on what’s boiling, what’s freezing and, most importantly, the pressure involved!