LabLulz Presents:nA Renewable-Energy Death RaynnSoundtrack: "Moonloop", off Porcupine Tree's "The Sky Moves Sideways"nnBill Beatty's amateur...
LabLulz Presents:nA Renewable-Energy Death RaynnSoundtrack: "Moonloop", off Porcupine Tree's "The Sky Moves Sideways"nnBill Beatty's amateur science page:nhttp://amasci.com/nhttp://amasci.com/amateur/mirror.htmlnnShoutout to our sponsor Peter C. for bumming a cigarette.nn~~~Hazards and Warnings~~~n*This video involves high temperatures.n*Be aware of the location of the focus, and don't let it near anything you don't want to roast, especially body parts.n*Do not look at the concentrated sunlight. The light dispersed by the target in the focus is very bright; be aware that one will be 'night blind' by comparison after looking at it, even with sunglasses. n*Sunlight and tobacco smoke are known carcinogens.n~~~~~~~~~~~~~~~~~~~~~~~~~~~~nnI found this old satellite dish in the woods behind my house.What could I do with it? I'm too busy doing mad science to watch TV! First, I got about 250 of these 1 inch by 1 inch mirror squares off eBay.Then I got to gluin'! Here's the finished device: the concavity of the dish has been covered in reflective squares.It's like an inside-out disco ball.nnTaking it outside, it now focuses sunlight, rather than satellite transmissions.It readily ignites steel wool. Newsprint is charred and set smoldering and smoking.With a bit of wind it bursts into flame. Denim also rapidly chars, smolders, and ignites. It lights a cigarette, then chews through it.In a minute or two, it will burn a hole through a piece of bamboo.Most of the energy is in the form of visible light, which passes through glass without heating it. Sugar reflects light too efficiently to heat up on its own. But a couple bits of charcoal catalyze the photoabsorption. Once dark caramelization products form and absorb light, the reaction is self-sustaining. Because it is flameless, it can safely heat volatile organics, like this paraffin. nnWe can try to measure the power being delivered by heating a known quantity of water and recording a time series of its temperature. Here is a graph of the measured temperature, as time goes on. The period where a cloud rolled across the sun is readily apparent as a stall in the rising temperature. We can use linear regression to estimate the heating rate over the whole experiment, or during the sunny episodes specifically. Here's the measured heating rate in degrees Kelvin per second nfor the first and second sunny periods, and for the whole experiment. Using the volume of water heated, the heat capacity of water, and the definition of the Watt, the power delivered to the flask can be calculated. Estimates range from ~26 to ~47 Watts. We can divide the measured wattage by the reflective area (230 one inch squares) to find the incoming power flux.The WMO describes daylight as 120 W/m**2 or more, so these figures are at least in the ballpark. We can measure the flask bottom (diameter 8 cm), to estimate the power flux it absorbed. nThese estimates range from ~5 to ~9 kilowatt per meter squared. Much of the power is concentrated into an area roughly this size of a mirror chip. This makes sense, since a perfect focus would be a couple hundred of these 1 inch square reflections right on top of each other.Assuming a perfect theoretical focus of 1 square inch, we calculate a maximum power flux . The estimates range from ~40 to ~73 kilowatt per meter squared.nnThis project was inspired by AmaSci, where Bill Beatty has been stockpiling cool ideas since the Web 1.0 days. Check it out if you're bored and looking for something to do!nnThanks for watching, and stay tuned! Less
