| Author | Message | ||
     Gary |
Crooke's Radiometer (Light Mill). I've been fascinated by this 'toy'. Could this be built easily out of everyday objects?. Questions I'd like to know the answer to with this 'toy': Does it defy Cantors heat cycle in efficiently turning heat into mechanical energy? Does the temperature escalate both on the vanes and the small amount of gas in the radiometer? How significant are the effects of light pressure and drag in the partial vacuum? What is the overall efficiency of this 'toy' in converting light into mechanical energy? | ||
| Gary |
Sorry 1st question should be Carnot NOT Cantor! ie To be more explicit; Does the light mill beat the Carnot Cycle (the theoretical limit for all heat engines?) in terms of efficiency for a heat engine? | ||
| Anonymous |
What makes you think that this device is a heat engine? All it does is absorb photons on one side while reflecting them on the other, transferring the momentum from the photon to the vanes. This has little to do with heat, it is similar to the turbines on a hydroelectric generator, just with light instead of water pressure. | ||
| Simon Quellen Field (Sfield) |
Actually, that is completely incorrect. If it were so, the radiometer would revolve in the opposite direction. It would also work in a complete vacuum, but the radiometer needs some gas to remain or it doesn't work. What is going on is that the black side gets hotter than the white side, and the gas molecules on the thin edges between the two sides see a gradient of temperature, and migrate from the cold side to the hot side. It was once thought that the gas mollecules hitting the hot side recoiled faster than those on the cold side, but this has been disproven. | ||
| Anonymous |
Bah.. the internet and its stupid misinformation, my mistake =-( | ||
| Simon Quellen Field (Sfield) |
To reply to the original question, the radiometer is very innefficient, and is nowhere near the Carnot limit. You should be able to improve the performance by using a screen instead of a sheet for the vanes, or by slicing slots or drilling holes in the vanes, or making them out of wire. But the efficiency will still be down in the dirt. The radiometer can barely move against the low friction bearing. A small solar cell the size of one of the vanes can drive an electric motor that has millions of times more power than the radiometer. ANd that is at less than 10 percent efficiency. | ||
| trickyeve |
If you guys want to get the full story get copies of the following papers, most of the information found on the internet is wrong, they keep referring to the explanation of Mr W. Crookes, the inventor of the Light Mill (Crooke's Radiometer). If any one happens to find any mathematical explanation or equations for the Light Mill please e-mail me the source or URL, Thank you. Jay Perez trickyeve@hotmail.com Original papers by Maxwell and Reynolds: "On stresses in rarefied gases arising from inequalities of temperature" James Clerk Maxwell, Royal Society Phil. Trans. (1879) "On certain dimensional properties of matter in the gaseous state" Osborne Reynolds, Royal Society Phil. Trans., Part 2, (1879) | ||
| Anonymous |
RE: Radiometers This is sad news for the romantics who wanted to believe they were seeing the direct effect of light photons bouncing off the vane and not just a fancy form of wind. So it begs the question; If the vacuum was empty enough, the bearing frictionless enough and the vane surfaces respectively dull and reflective enough, would the vane spin the other way round and give us something to really marvell about? Please say yes! | ||
| Simon Quellen Field (sfield) New member Username: sfield Post Number: 77 Registered: 12-2004 |
Yes. | ||
| Anonymous |
....and has it been done? | ||
| Simon Quellen Field (sfield) New member Username: sfield Post Number: 80 Registered: 12-2004 |
Not all of the stuff you find on the web is wrong. Read this article for example. A mirror of the article is here. The Wikipedia brings Einstein into the picture, as does this excellent article. An interesting application is here, where the effect is used to drive the pendulum of a clock. | ||
| lysdexia Unregistered guest |
I wrote something about this, an ideal embodiment, in the advancedphysics.org thread "Mike's Saturday Conjecture". Then I got to put down a physics major in talking about glass and infrared...  | ||
| Ken Eatherly (Unregistered Guest) Unregistered guest Posted From: 68.40.106.134 |
It's interesting that even an ordinary science museum gift shop-quality radiometer will work in a dark room just from the heat of one's hand. (Actually, of course, it's from the light our bodies give off -- infrared, to be exact). | ||
| Simon Quellen Field (Sfield) Senior Member Username: Sfield Post Number: 750 Registered: 12-2004 |
Have you actually tried this? I have several, and they won't work inside my windows because the windows absorb too much ultraviolet light from the sun. The window sill is warmer than my hand, from absorbing the sunlight, but the radiometer won't budge. Direct sunlight, or close proximity to a light bulb will make it work. But my hands don't seem to have any effect. | ||
| mnado (Mnado) Senior Member Username: Mnado Post Number: 129 Registered: 12-2005 |
so if this is light mill creating any power(voltage?amps?) does light mill work as a solar cell? is it just a vacuum tube with wire to make something work or it it just made for the experiments if this is to make power,how does it produce one? can you use mirrors for the vane,or is it too heavy? matbe a substitute is a foil,how much air do you have to leave inside to make it work? what is the effect of getting many air out of the bulb? (Message edited by mnado on January 31, 2006) | ||
| thinktank paul (Thinktank) New member Username: Thinktank Post Number: 1 Registered: 3-2006 |
hiii...i am presently trying to build such a radiometer and trying to optimise the size for maximum efficiency. if somebody has the paper published by Reynolds in 1879 , or the one by maxwell, could you please send it over to me? my email address is dibyadeep@gmail.com thanx... | ||
| Troy (Pharoah) Intermediate Member Username: Pharoah Post Number: 38 Registered: 3-2006 |
" so if this is light mill creating any power(voltage?amps?) does light mill work as a solar cell? is it just a vacuum tube with wire to make something work or it it just made for the experiments if this is to make power,how does it produce one? can you use mirrors for the vane,or is it too heavy? matbe a substitute is a foil,how much air do you have to leave inside to make it work? what is the effect of getting many air out of the bulb? " The vanes spin, but there is no connection to the outside. Very little "power" is produced, so it could not drive a generator. | ||
| Daniel Bitton (Daniel_b) New member Username: Daniel_b Post Number: 1 Registered: 4-2010 |
New in the neighbour I am fascinating to build a 6" dia. radiometer in a glass bell I tested it at 30 in/Hg vac with no problem Could someone let me know: 1) Is there any limitation in size for building a crookes radiometer? 2) What is the best material to cut the vanes? 3) White or shiny aluminum? 4) Flat black or other? 5) How much in in/Hg should be the optimum vacuum? Thanks form melbourne Daniel |
