Shaped Wind Charges

Question

I have a character that can create compressed air spheres. If you were to create just a normal sphere of compressed air, it would expand in all directions equally at a speed and force that would depend on how compressed you made the air. While that certainly can be useful under the right circumstances, its far more useful to be able to focus the air burst in a specific direction. Here are the limitations:

• When it comes to creating air, this means he has the ability to create any molecular structure that's a gas at room temperature and it is created at room temperature - though note that the more unnatural the gas is, the harder it is for him to create. Oxygen is fine, sulfur hexalfuoride can only be created in limited amounts.
• The character uses a magic ability to create air within a six-inch sphere of his choosing. The sphere is created at chest level about a foot in front of him. He can choose where any air is added within the sphere - for instance, he can add extra oxygen to the left side and nitrogen to the right if he so chooses.
• He cannot destroy air or move it - his ability is restricted to creating it. He can't have one side of the sphere be a vacuum, for instance, or do anything about the normal atmospheric air that's already in the sphere.

Given these restrictions, I thought it might be possible to create something resembling a 'shaped wind charge' - when crafting the sphere, the character uses a highly-compressed glob of lighter air, surrounded by a not-as-compressed shell of heavier air which serves to dampen the expanding lighter air and focus a blast in one direction.

The three limitations cannot be violated, though if it can only be done with large amounts of rare gasses, it is what it is. Tools (i.e. a gun facsimile) are not allowed, the goal is to do this using created wind only. So, the question is: what's the optimal gasses to use for such a shaped wind charge, and how effective will that end up being?

There is a hard-science tag applied to the question because I want very specific gasses.

Answer 1

There are 5 effects I think have been overlooked here.

First, the obvious uses; Anything a nitrogen canon can do, this can do better, as its maximum pressure seems to he unbounded in the question, and the sphere can easily be placed near or in things to strengthen the directional focus, (we cant use other gasses to build a cone cause they'd mix together). A small hole in the ground is all that's needed to get a launch. Nitrogen canons are used in special effects to flip cars or launch buses over bridges, I'm just going to answer this section by saying "Buy the Mythbusters box set and watch them launch stuff with a nitrogen canon", and move on to what I think is the more interesting use cases:

The pressure wave can be a sonic weapon

Build the pressure up large enough, release it suddenly, and you've deafend everyone in the blast zone not wearing ear protection. Extremes could result in permanent hearing damage, unconsciousness, or death. Fill it with air, face it at your enemy, fire, their eardrums burst.

Gases change temperature when expanding

Checkout the https://en.m.wikipedia.org/wiki/Joule%E2%80%93Thomson_effect.

The gases are created at room temperature yes, but as soon as the shield is dropped, that's going to change.

Hydrogen heats up when expanded from high pressure at room temperature, oxygen and nitrogen cools down when expanded from high pressure at room temperature. This gives your character the ability to heat or cool anything. Side stepping your rules about temperature.

Hydrogen auto ignites at about 550 degrees C, so I believe (open to correction here) enough hydrogen crammed into that sphere at room temperature would expand and heat further and further until it reaches auto ignition, and turns into a massive fireball when the shield is dropped.

Perfect stoichiometry is possible.

You can create gas mixes, so 2 parts hydrogen, 1 part oxygen, perfectly mixed, and packed to crazy levels of pressure, is an https://en.m.wikipedia.org/wiki/Oxyhydrogen bomb. This auto ignites at about 550 degrees, and self heats when the shield is dropped same as normal hydrogen.

Burns at 2800 degrees C.

You could also combine this with a tiny forward facing hole in a container to use as a flamethrower / blow torch.

You can mess with the weather.

The ability to create a lot of air at 25 degrees (room temperature) can create or destroy weather features. At the very least warm moist air at sea level suddenly getting pushed upwards by an expanding sphere of air? Instant vertical cloud with moisture travelling upwards through freezing conditions. That's a thunderstorm.

I reckon you could make a hurricane with a few well placed pressure fronts.

And why not crank the pressure all the way up?

Theres no limit on the pressure apparently - just the more common the gas, the more you can create.

Can we get enough nitrogen or oxygen packed into a six inch sphere to create a black hole?

At first I thought "enough to create liquid - too much", but rereading the question I'm getting the impression this forces the substance to exist as gas at room temperature regardless of density.

Answer 2

It's not possible.

At least, not with the restrictions provided. With only the ability to create compressed sources of gases, we have lost the ability of most of science to help us model the effects fully. Any containment mechanism would have allowed this to work as a spontaneously created high pressure zone with containment is just like any other air compressor which we can probably find studies about the decompression.

Additionally, since gases try to fill the container they are in and follow gas laws. The important one here is "momentum and energy is transfered not lost during collisions". Heavier gasses will absorb more energy to move and will be affected less when imparting energy but, the expansion will still occur. "Gases expand spontaneously to fill any container" means that without a container to block expansion or absorb directional energy, We can't directionally fire gases.

However, if instead of just creation of gases at a set point, we can add directional momentum to it. This means that overall, the gases will tend to expand in the direction of the momentum due to the transferred energy being kept.

Answer 3

As is pointed out in the comments, the gases would mix. This answer is assuming that all the gases are placed instantaneously upon the release. You wouldn't be able to funnel the air fully, mostly because it wouldn't be possible to fully shape the air inside, leading to an area of fastest and slower air emerging. As far as raw elements go,A quick google search states that Tungsten Hexafluoride, while being a quite complex chemical, is one of the most dense gases currently known. It would work best as your "Shield", but correct me if I'm wrong. I don't major in this subject. Common sense states that you want an incredibly light gas, such as hydrogen or helium, to function as the payload of the wind charge.

Another thing I've found is that it would be possible to make a gaseous "bullet" using Xenon, Fluorine, and hydrogen. You would make a dense-ish outer shell of Xenon, Radon, or some other inert gas, have a Hydrogen secondary shell, a fluorine core, and a dense pocket of nonreactive (or highly reactive, I don't really know as this is just a crazy theory) gas to function as the "Bullet" of the weapon.

Please, don't hesitate to correct me on any of this. I don't have that much experience, and thus shouldn't be trusted as a major authority on the subject of wind charges.