In a hypothetical situation where liquid water can flash freeze in its entirety, what would happen to the energy in it? Is it enough to feel, cook or explode something inside or around the ice?

Assuming a 10 cubic foot cube of water or 283 liters, at 20 degrees C. It freezes instantly, 1 second or less. I found a number that it would take removing 417 kj to bring 1 liter to 0 C and crystallize it. At 283 liters that's 118 Megajoules. 32 kWh, 66 lbs/29 kg of TNT equivalent. 118 Mega Watts released as heat in a second.

  1. Are my numbers above correct?
  2. Would this energy be released like a simple heat wave, or an explosive similar to tnt? Convection?
  3. I am assuming that even if just heat, anyone feet away or worse in the middle would suffer significant injuries, right?
  4. Can water freeze this quickly?
  • $\begingroup$ You seem to be assuming that 417 kJ of heat is "hot" (aka high temperature). This is not the case. That 417 kJ would have a maximum temperature of 20 deg C. $\endgroup$ Aug 29, 2022 at 16:47
  • $\begingroup$ @DavidWhite no I'm assuming that Megajoules are megajoules and releasing that much energy in a short amount of time would have certain affects. So all you are saying would happen is 118 megajoules released in 1 second would what, warm the surrounding air 20 degrees to 40 C? $\endgroup$
    – cde
    Aug 29, 2022 at 17:20
  • $\begingroup$ No, what I'm saying is that 118MJ at 20 deg C would warm some cooler object to 20 deg C. Heat is not the same thing as temperature. $\endgroup$ Aug 29, 2022 at 22:50

1 Answer 1


There are two ways to freeze liquid water.

The first way is passive cooling - place the water in an environment that is at a temperature below $0^o$C. The water cools until is is at the same temperature as the environment. In this case the energy released by the water is absorbed by the environment, raising its temperature, but if the environment is large enough and cold enough (e.g. a large tank of liquid nitrogen) then the final temperature of the water and its surroundings will still be below $0^o$C.

In this first case the rate at which the water freezes is determined by its surface area and the thermal conductivity between the water and its environment. It is certainly possible to flash freeze small amounts of water in this way. Possibly $200$ litres of water could be flash frozen if you turned it into an aerosol first.

The second way is active cooling using a heat pump to remove heat from the water. This is how ice cubes are made in a freezer. In this case, the energy extracted from the water plus the additional energy used to drive the heat pump all go into heating the environment. To extract energy from the water at the rate of over $100$ MW you will need some tens of megawatts of power to drive the heat pump - this is roughly the power output of a large locomotive or a large jet engine.

In the first case you wouldn’t want to be close to the water because you would also freeze. In the second case you would want to keep away from the hot exhaust of the locomotive or jet engine.


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