Want to be clear here, talking about EXTERNAL spray not internal.
I think the issue I have with misting directly ON the IC rather then trying to cool the air flowing over the IC is that air flows thru an IC more evenly, mist will not. A mist will most likely just contact a smaller surface area so you end up cooling only a small section of the IC. Cooler air will flow better and provide a more uniformed coverage.Misting is based on the theory of Evaporative Cooling (or Desert Cooling), which uses the scientific principal of Thermal Dynamics, which states that water requires energy to evaporate, or 600 calories of heat per gram of water, and this heat is taken from the environment.To achieve this water is forced through a very small orifice creating a very fine mist or fog of ultra fine 50 micron water droplets (smaller than the diameter of human hair). Once these very fine droplets of water are exposed to the hot atmosphere, they quickly absorb the heat present in the environment and evaporate in the process. This quick heat exchange is known as Flash Evaporation, it takes heat from the surrounding area, and drops its temperature by up to 35 degrees F, and consequently the air is cooled.
High Pressure misting generates Fog, which is ideal misting, with finest mist. However the cost is way high too, because it uses high pressure pumps, and stainless steel tubing, and metal fittings to handle the high pressure. The finer the mist, the more efficient is the system (due to the larger surface are), and the higher the pressure the finer is the mist produced.