Have you ever fired a PCP(pre-charged pneumatic) air gun? No phase change; much icing. Yes, the latent heat of phase change makes an enormous difference, but it

Have you ever fired a PCP(pre-charged pneumatic) air gun? No phase change; much icing. Yes, the latent heat of phase change makes an enormous difference, but it doesn't mean that the pressure drop alone won't cause a big enough temperature differential, and since you're not in a closed compression/decompression loop, you wouldn't be particularly worried about the efficiency -- you're just using a byproduct of the propulsion system that would otherwise be wasted.