I need some help with a steam generator project

greg_gory_o

I need some help with a science project. 

My son has decided to use mirrors to reflect the suns light into a focal point.  The focal point will be on a metal container filled with water.  As the water turns to steam it will power a small air compressor (the ones you plug into the cig lighter).  As the steam turn the engine the motor should produce DC voltage.

We have cut (6) mirrors 6"x6" or 15.2cmx15.2cm.  Getting the focal point small enough to make any heat has become a task.  Is there a better way to gather the suns rays?  Maybe concave or curved mirrors?  Should he use refrigerate instead of water, to boil faster?

Any help is greatly needed, as the project is nearing the deadline (about three weeks away).

nicholas bonham-carter

Solar oven

I saw a YouTube video of a solar oven used for setting 2x4's on fire, made from an old satellite antenna, which has the appropriate parabolic shape. Mirror pieces were glued on the surface, but I think that polished foil would be better.

Be careful, as any sort of boiler can explode without some sort of pressure relief!--NBC

Rod

Science Project

Hi-  LOL - After reading NBC's suggestion on using a TV parabolic, since it's science project season, I'm guess I'm  going to have to keep an eye on my Direct TV antenna! :

    I'm afraid the steam section of this website deals more with residential steam heating so most of  us don’t have much experience with what you are asking.  I can sympathize with you as I’ve had to help out in my kids on similar science projects in the past.

    Not based on any sound engineering principles other than a wild guess, my initial thought is that you have no where near enough solar radiation using those size mirrors to generate enough steam to power the compressor you are suggesting to use.  If the mirrors were 6 feet x 6 feet I would still question whether they are big enough. As for boiler size I would think you would need something as large a 5 gal container to get the volume of steam you would need. Try blowing through the pump and you will get an idea of what I mean.

Ideas & Thoughts

I’m not sure that on the scale of size the mirrors you intend on using would be able to power any device that would then generate electricity. You might just want to see if you can just power a moving engine

   One of the first things I would do is come up with my “sun source” - something in the way of a heat lamp to reflect off the mirrors and power the system. Being winter this is probably acceptable alternate to the real thing



You might take a look at this small steam engine which is on Amazon .com. In the search window use the words - Model VI Steam Engine.   You might be able to take the boiler and engine and modify it to fit your needs. I would still question whether you could get enough heat from the mirrors to power this system.



Thinking it over I think you best bet might be look into Sterling Engines. Sterling engines need a lot less heat to power them.  I looked on the internet and this website seemed like it might have possibilities.  http://www.stirlingengine.com/product/25

Good luck with the project!

- Rod

Jamie Hall

Rod has an excellent point...

The effective solar constant is somewhere around 1 kw of power per square meter -- and you should derate that by at least half for practical purpuses.  Your problem with the plane mirrors you are using is that you may not be able to get enough power concentrated into a small enough area (the minimum spot size will be the size of each mirror -- 15 cm x 15 cm).  Your lad should figure out how much power he needs for that compressor, and then figure how many mirrors he needs (cheat sheet for dad: it will take about 100 mirrors per kilowatt).  And go from there.



It's not quite true that Stirling engines take less heat than others for a given power output -- that would violate the first and second laws of thermodynamics -- but they can get by on lower grade (lower temperature) heat.  Since heat loss from your "boiler" may be a problem (that's proportional to temperature) they might be helpful.



You could also try a lower boiling point medium, such as alcohol, but keep in mind that water is pretty benign if something goes wrong, and all of the lower boiling point things tend to to be more or less nasty -- poisonous, or flammable, or corrosive, or some combination...



Good luck!