Still trying to "expand" my knowledge.. My thoughts today on both Air Entrainment and Steam your mileage may vary.
Air entrainment is not referring to pushing fire, but the simple fact that as a jet or stream of water is produced it displaces air in front of it, hence creating a lower pressure causing the higher pressure air around it to flow into the path. It is mechanical force acting on both products of combustion and products of extinguishment. Along with expansion & contraction of fire gases, which comes from gases both cooling and heating impacted by phase conversions of water and steam both condensation and evaporation.
It relatively easy to impact the flow of gases within a structure both by controlling vent path and by forcing it around via stream application. This is why many of us have argued for a water stream that produces the least amount of air entrainment along with the most contraction and cooling, while minimizing steam and expansion.
Solid or Straight handline streams can offer a high application rate and a low reaction force when configured correctly. This is the gold standard of critical flow.
Fog patterns on the other hand displace much more air. Air entrainment is massively increased over a jet of water resulting in displacement measured in cubic feet per minute. They also produce a finer droplet which easily converts to steam creating expansion and cooling surface fuels less effectively.
To close out my thoughts here are a fedw snippets from PhysLink.com:
Question:
Is the popular belief that 100C° (212F) steam is more injurious to the skin than boiling water (212F) just a wives tale?
Asked by: David
“ There’s more energy in the steam. To raise the temperature of one gram of water from 37�C (temperature of skin) to 100�C (the boiling point) requires 63 calories (one calorie per degree). To convert that gram of water to steam requires another 540 calories. So the energy in the steam is 9-fold greater than the energy in the same weight of water at the boiling point. This energy (as heat) is released when the steam condenses to water and the water cools to the temperature of skin. Steam will be substantially more injurious. There’s more energy in the steam. To raise the temperature of one gram of water from 37�C (temperature of skin) to 100�C (the boiling point) requires 63 calories (one calorie per degree). To convert that gram of water to steam requires another 540 calories. So the energy in the steam is 9-fold greater than the energy in the same weight of water at the boiling point. This energy (as heat) is released when the steam condenses to water and the water cools to the temperature of skin. Steam will be substantially more injurious.
Answered by: David Kessel, Ph.D., Professor, Wayne State University, Detroit”
“Steam burns do have to potential to cause more damage than scalding. The reason has to do with the latent heat of vaporization. This is the amount of heat energy necessary to change the phase or state of matter from liquid to gas. This energy is absorbed by the liquid, but does not change the temperature. Conversely, when a gas condenses, it must release this latent heat and become a liquid before it can cool below its boiling temperature. The latent heat of vaporization for water at sea level is about 2250 J/g, as compared to the specific heat of water of about 4 J/C. All that extra heat has to go somewhere, mostly to the surrounding air. If, however, you place your hand into a jet of steam, much of that heat will be absorbed by your skin - very unhealthy. And what’s worse, as the steam condenses onto your skin, it will still be at 100C!
Answered by: Grant Coble, B.S., Physics Teacher, Hollywood High, Hollywood California.”