Saturday, March 19, 2011

Working Freeze Gun

The other day I ran into someone I hadn’t seen for a while and they asked me why I didn’t use my genius for niceness instead of evil.  What nonsense.  If you're an evil genius and you stop being evil, they you will just be a common genius and what would be the point of that?  To that end here’s my first Supervillain Workshop: Building a Freeze Gun.  Building a working freeze gun is actually really easy.

At its core premise this freeze gun spurts liquid nitrogen (LN2) via the power of compressed gas.   A simple one could be built by converting a paint spray gun. The down side is most of these devices work of mains power supply.  There’s the hassle of getting out the extension chord, finding a convenient power outlet, if you’re in a foreign country you need the correct adaptor and there’s always the risk that some kid disables your super weapon by pulling the plug out when you’re not looking.  Overall it’s an unprofessional look.

What you want is a design similar to a portable, three tank flame thrower having two fuel tanks and one compressed gas tank.  There are many advantages to a freeze gun over a flamethrower.  Primarily being the type of weapon it is, a freeze gun doesn’t need the ignition system a flame thrower does.  Additionally with a flame thrower the fumes from the fuel give you a headache, you have to clean burnt debris of the gold bars, and besides every man and his dachshund has a flame thrower.  Nitrogen is odorless, colorless, tasteless and evaporates away leaving no mess.  On top of this anyone who remembers their Adam West lore will recall that Mr Freeze was always surrounded by the most attractive minions in fur-lined, eskimo hooded miniskirts.  A freeze gun is by far the choice for the decerning mastermind.

As can be seen in Diagram 1, the pressurised gas connects to the LN2 tanks.  To avoid any unwanted reactions it’s probably best to use nitrogen (N2) as the compressed gas.   The pressure from the gas pushess the LN2 through the delivery hose into the hand held section.  The liquid tanks have screw on tops for easy refill and are vacume flask in design, not unlike your drink thermos, to prevent tempreture transfer between the environment and the LN2 sitting on your back.  The expansion rate of LN2 into gas is 1:694 which is an aweful lot of unexpected pressure if your tanks heat up. 

Safety tip: Use steel not brass valves. In 2006 the pressure-relief devices of a tank of liquid nitrogen at Texas A&M University were sealed with brass plugs. As a result, the tank failed catastrophically and exploded. The force of the explosion was sufficient to propel the tank through the ceiling immediately above it.  Fortunately, the dean always said he would like a skyelight.

The hand held section consists of a simple valve kept in place with heavy springs.  When the trigger is squeezed it releases the valve sending the pressureised LN2 to the nozzle which adjusts the spray acording to taste.  A flamethrower of similar design can shoot it’s stream about 45 meters.  Half that range is plenty for a domesic level freeze gun.  Because of the evaporation of the  liquid nitrogen when it hits the surrounding air this will reduce the effective range.  You may need to experiment with the nozzle to get a good compromise of distance and spread of the stream.  Wider spread will saturate your taget better but at the cost of distance.  If the spread of the stream is too wide evaporation will inhibit saturaion.  A bit of testing on the neighbours plants should help you find the right balance between distance and a coverage with the stream.

Safety tip: Handle liquid nitrogen with care.  Because of it’s extremely low tempreture inproper handling can result in cold burns and frozen limbs or pets.  Be sure to wear an insulation suit.  The suit will also have good intimidation value in the field and let the guards to the casino valt know you mean business.  I recommend sticking with a clasic silver suit, if you wear a green or camoflage suit you’ll look like a paramilitary extremest and people wil think you’re crazy.

Now you’re ready to strap those potentially explosive canisters of  freezing death to your back and away you go!

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