I have a question that I was thinking about for a long time. I live in Kuwait and in the summer season the weather reach 50°C which is extremely hot specially inside a car.

What if I was able to quickly cool the inside of my car using Dry Ice cold vapour from a tank cylinder to fill my car in few minutes, Would the glass break when the cold vapour get in contact with the Hot car windows? What problems might happen? I am hesitant to try it.


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  • $\begingroup$ 50-60 years ago it used to be fairly common for auto windows to break when the car was left out with the windows rolled all the way up on a hot, sunny day. But this is rare anymore. $\endgroup$ – Hot Licks Dec 25 '17 at 15:41

Most car windows are pre-stressed: during the manufacturing process, a significant stress differential is "baked in" to the window. This means that the inside of the glass is under tension, while the outside is under compression. One result of this is that windows can seem to have colors in them when you view the sky from inside the car using polarized glasses.

The reason for this pre-stress is that it makes the window more resilient to small cracks - if you hit a small stone, the impact will create a tensile wave on the surface. Normally such a wave can cause a crack to propagate through the glass - but by pre-stressing the glass, the crack is "held shut" and the crack is no more than a chip. If you hit the glass hard enough, your crack can grow from the compressed region to the region under stress, at which point the crack will grow unimpeded.

This is why car windows used to "shatter" into many small pieces with larger impacts - incidentally, this is typically safer than having a few large pieces of glass: while you end up cut by many small pieces, it's more likely you would be killed by a few large pieces.

All this is a prelude to the answer: "it depends". Windows are made to be quite resilient, but the manufacturing processes vary enormously. However, if you simply placed dry ice inside the car, the rate of heat transfer would almost certainly be too small for a "normal" window (which does not have pre-existing cracks in it) to fail. But the devil is in the details - mostly, "how quickly does the window cool down, and what does that do to the stress distribution". Which is impossible to answer in the general case.

Incidentally - when the temperature "outside" reaches 50°C, your glass (and the inside of the car) might be significantly hotter. But that's a topic for another discussion...


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