Tuesday, May 24, 2011

Vortex Tubes: A Low Tech Solution to Cooling Magnetic Sails

         In yesterday's post I mentioned using Robert Zubrin's idea for Magnetic Sails to move giga-ton asteroids into new orbits.  The idea has a lot of merit; un spool a thousand kilometers of superconducting wire, add power, and you have a sail big enough to move mountains with solar wind.  The problem with Zubrin's proposal is one of the main problems with all engineering in space: Heat disposal.  Making the wire thin enough to use means it's so thin that it cant radiate the heat it's making fast enough.  This seems to be a deal-breaker, even in science fiction like mine.

          There is, however, a possible solution: Vortex tubes.  Vortex Tubes have been around for decades as a cheap way to refrigerate using only compressed air and no moving parts.  The tubes themselves are so easy to fabricate that we're doing it already, in Ghana.  One of MIT's Fab Lab projects is in that African nation providing technological solutions through the use of the industrial infrastructure inherent in the fabrication model.  In this case, Vortex Tubes are being used to solve the problem of food spoilage, which claims a third of Ghana's produce.  It's an elegant solution; by hooking up the tubes to a truck's air compressor, you get refrigeration with no moving parts and now extra power consumption.  As long as the truck's engine is running, the food stored within is safe.

          This system can be used in magnetic sails for asteroid moving.  by making the outer skin of a Vortex Tube out of superconducting elements, the tube itself will keep the system cool.  Simply have air moving through the tube and the heat disposal problem is solved.  Right?

          Silly RocketFans, nothing in space is ever that simple.

          The use of the VortexTube is an inspired solution (if I do say so myself) but it only moves the problem somewhere else.  The heated air in the Tube must be cooled or the system will eventually just separate hot air from hotter air and the whole thing will vaporize.  This means that the surface of the asteroid must have enormous radiators, or heat sinks.

          I'm in favor of heat sinks, because that waste heat from the sails can be valuable in the asteroid itself.  From what I understand, a heat sink kind of ideal for asteroids anyway, and can be as simple as a block of ice.  It is useful for short-term waste heat; any longer and the ice begins to boil or the rock starts to melt.  It occurred to me, if one of the purposes of asteroid mining is propellant production, then this is a good thing.  Let the "waste heat" from the sails and the fusion plant that powers them melt the ice in an iceteroid so that the liquid water can be cracked for hydrogen and oxygen.

          So there you have it, RocketFans; by using the simple, primitive Vortex Tube in our Magnetic Sail design, we create a closed-loop system that cools the sails while heating up the ice (cryolith?) of an iceteroid for propellant mining.  All with no moving parts.  I call that an engineering win.

           That being said, I am not an engineer, so your thought are appreciated in the comments section below.

           See you tomorrow, RocketFans!


  1. I like it, but I am no engineer either.

  2. I'm no engineer either, but it looks elegant on first glance. The biggest issue is that waste heat frequently isn't 'dense' enough to be useful. So how much heat do super conducting magnetic sails put out per unit of volume?

    In short, those pesky laws of thermodynamics might keep it from being too useful.

  3. Vortex tubes are devices that separates compressed air into hot and cold currents. The unit doesn't have moving parts, and provides a powerful separation and value of hot and cold air for industrial uses.


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