Teenage Mad Scientist Creates Solar Death Ray

[Devil's Due]

hundreds of fat large mirrors just randomly placed

Doubt Archimedes did it randomly... bud.

If he ever did it at all, which has been proven that no, he did not... buddy.

 

[Archemetis]

IT HAS THE POWER OF 5000 SUNS!

AND I SHALL HOLD THINGS IN FRONT OF IT WITH MY BARE FINGERS!

Pretty awesome Death Ray, shame it was destroyed.

 

[Gritimo The Odd]

Didn't the Mythbusters prove this was impossible?

Mythbusters actually did show what this guy did was possible, and in fact had been done before. The episode everyone has quoted so far and is most likely remember is the Archimedies death ray, one of their earlier episodes. One of the myth revisited episodes they came back to the subject and actually had a high grade scientific parabolic mirror which they used to set several things on fire.
http://www.youtube.com/watch?v=T3udgbHjWCs&feature=related

 

[Magicman10893]

I think Mythbusters needs to re-re-re-revist this myth.

 

[Gearran]

Notice how close the guy has to hold the object to the dish in order for it to focus properly. It only works from a couple of feet away. Now, he COULD change that by altering the shape of the dish, but aiming all of those things at one point again would be a pain.

There is something called the inverse square law. As pertaining to intensity:
The intensity of light radiating from a point source is inversely proportional to the square of the distance from the source; so an object twice as far away, receives only one-quarter the energy.

This is why something 2ft away from the mirror could be at 800F, refocus the mirrors at 4ft and they would only be 200F.

This is true! However, the point I was getting at is that the beams that reflect from all of those tiny mirrors focus on a specific point a couple feet in front of the dish. Any further away and the beams become a lot more diffuse, which in turn means that the heating effect is far less effective (if functional at all).

 

[imperialwar]

Talk about people griping about the same thing and not reading posts before them...
Ok, maybe its not 5000 suns, so maybe he should have used candle power like they use when describing the light emitted by light bulbs. Or maybe a new measurement: SFP or solar focal points.
Second Mythbusters are SPECIAL EFECTS TECHNICIANS, NOT SCIENTISTS, hense i dont watch them for their science but their ability to perform special effects to at least try to replicate the science. If you watch Mythbusters especting perfect science then obviously you are watching the wrong show. For the record i like watching the mythbusters.

I would love to see this thing in a larger scale, instead of 5000 smaller mirrors maybe precisely angled mirrors the size of the ones used by the mythbusters, then we will be cooking with gas... or should that be burning with sunrays. But then i guess then it wouldnt really up the power using bigger mirrors, as they still only reflect the sun once. Maybe a perfect "cup" shape with a focusing crystal, so the beams bounce back and forth in the device then are angled out by the crytsal.. i dunno, grasping at straws a little to try to magnify the power then avert it out as a weapon grade item

 

[veloper]

Simple magnifying lenses are more effective and less of a hassle.

That is not true, for the same reason no one builds refracting telescopes anymore.
His "mirror" has a diameter of about 1m
this would collect the same amount of light as a magnifying glass 1m wide
largest refracting telescope in use diameter ~1m
So his 5000 little mirrors equates to a massive piece of perfectly formed glass
also the refractor would have to be reletively close perpendicular to the sun, so you couldn't aim it

1. you don't need that much power. You can already burn holes in stuff with modest lenses. Try it.

2. it's all about focus. His mirrors are flat so they never concentrate light at one small point, but instead heat up a larger area. A lens is far more efficient.

1. I try it all the time, I have a laser pointer that can do that when it's cloudy. But can a small magnifying lens put a hole in metal and instantly light pieces of wood on fire? Probably not.

2. His mirrors are flat, yes, but they are all positioned at different angles, essentially creating a parabolic mirror which does concentrate light at one small point.

3. Again you can't aim a magnifying lens anywhere besides almost straight down.

1. A small lens can't burn a hole in metal, but it can most definitely start a fire.

2. Only with curved mirrors would you get one small focal point. With flat mirrors you can only approach that if you break it up in ever smaller pieces and then you'll never quite get there.

3. With the mirror you cannot even do that. The mirror cannot aim straight down. It's not like you can aim everywhere or that it had a good range. It's barely even portable.

 

[ReverendJ]

If he ever did it at all, which has been proven that no, he did not... buddy.

And again, this "proof," it comes from Mythbusters, yes? A source I personally do not find credible. They've been wrong before, and I have observed their methodology and found it wanting. So be prepared to give some potential credit to our poor, backwards forebears who made do figuring all this stuff out without textbooks and people telling them how it worked and whatnot. Y'know, the innovators.

 

[reciprocal]

I'm going to call this fake. Given the approximate size of the dish I estimate that he'll have at most 1kW to 2kW at that point (based on peak insolation over an estimated 1 - 2 m2 area and assuming there's no losses from the reflections, which is extremely unlikely). Even if we assume that the test tube of water somehow absorbs ALL of the radiation heat (given the transmissivity of glass and water)... there's no way water will boil that quickly.

Also the burn marks seem a little TOO precise. A perfect circle? Seems suspicious given the area of the concentrated light.

My guess? Perhaps a hidden laser somewhere that is masked by the reflections from the mirrors.

Simply put, there's a reason why the Mythbusters failed. As flawed as their methodology (especially the recent episodes) is, there's some underlying basic physics/chemistry at work.

He's getting 82W delivered to an area slightly over 1 cm2, which will raise the temperature of 1 mL of water a bit over 20 degrees C in a second, which means if it started at 20 degrees, it would boil in 4 seconds. There's more than 1mL of water in that test tube, but given the size of the tube it's a smaller (~16 mL) variety. However, we're not looking for boiling away the entire test tube of water, just enough to generate steam (localized boiling) as shown in the video. Looks to be about 8s for a decent amount of steam to appear, which gives us some leeway to account for absorption, thermal conductivity, and the unknown starting temperature of the water.

It's not impossible that they've used a laser, but seriously, if they've got access to that powerful of a laser to have the effects shown on the other example objects, what motivation is there to conduct an elaborate hoax? For the effort to collect and attach the mirrors to the dish and mount it to a wagon, they could instead grab some bricks to build a backstop (so they don't scorch/hole their neighbors' stuff) and then film themselves burning holes in things with a laser! There doesn't appear to be a glut of backyard laser shenanigans uploaded to Youtube these days.

Yes, but again I must point out that the boiling of water is extremely dependent on a lot of assumptions namely:
1) There is a sufficient area of blackbody objects in the water capable of absorbing 100% of the solar radiation, while maintaining the water boiling temperature at approximately 100degC
2) The 1 mL of water that gets raised by 20degC does not move out of the range of the beam's range due to natural convection
3) There are no heat losses occuring at all.
4) The water was preheated.

Most transparent fluids are notoriously bad at retaining radiation heat gain. All kettles use a heating element because conduction and convection are the best ways to transfer heat to water.

Of course he could have just used another chemical that has a close to ambient temperature boiling point but there's still too many coincidences to allow it to occur based on radiation alone.

My point of contention is that 82W should not be burning things so quickly. If this were so, there would be a lot of melted lamps because even though the 100W light bulbs distribute the flow over a larger area, they are also exposed to them for a longer time. Some of the effects that he is showing have to be about 1000degC or higher on materials that have high thermal capacity. If the parabolic lens was, say, 5m in diameter or so then I would believe it.

I can't prove whether lasers were used or not but people have pulled more elaborate hoaxes before. Plus, the skeptic in me finds the destruction of the original device in a shed fire to be too coincidental (sorry about the Conspiracy Theories, Movie Bob).

 

[vansau]

I'm going to call this fake. Given the approximate size of the dish I estimate that he'll have at most 1kW to 2kW at that point (based on peak insolation over an estimated 1 - 2 m2 area and assuming there's no losses from the reflections, which is extremely unlikely). Even if we assume that the test tube of water somehow absorbs ALL of the radiation heat (given the transmissivity of glass and water)... there's no way water will boil that quickly.

Also the burn marks seem a little TOO precise. A perfect circle? Seems suspicious given the area of the concentrated light.

My guess? Perhaps a hidden laser somewhere that is masked by the reflections from the mirrors.

Simply put, there's a reason why the Mythbusters failed. As flawed as their methodology (especially the recent episodes) is, there's some underlying basic physics/chemistry at work.

He's getting 82W delivered to an area slightly over 1 cm2, which will raise the temperature of 1 mL of water a bit over 20 degrees C in a second, which means if it started at 20 degrees, it would boil in 4 seconds. There's more than 1mL of water in that test tube, but given the size of the tube it's a smaller (~16 mL) variety. However, we're not looking for boiling away the entire test tube of water, just enough to generate steam (localized boiling) as shown in the video. Looks to be about 8s for a decent amount of steam to appear, which gives us some leeway to account for absorption, thermal conductivity, and the unknown starting temperature of the water.

It's not impossible that they've used a laser, but seriously, if they've got access to that powerful of a laser to have the effects shown on the other example objects, what motivation is there to conduct an elaborate hoax? For the effort to collect and attach the mirrors to the dish and mount it to a wagon, they could instead grab some bricks to build a backstop (so they don't scorch/hole their neighbors' stuff) and then film themselves burning holes in things with a laser! There doesn't appear to be a glut of backyard laser shenanigans uploaded to Youtube these days.

Yes, but again I must point out that the boiling of water is extremely dependent on a lot of assumptions namely:
1) There is a sufficient area of blackbody objects in the water capable of absorbing 100% of the solar radiation, while maintaining the water boiling temperature at approximately 100degC
2) The 1 mL of water that gets raised by 20degC does not move out of the range of the beam's range due to natural convection
3) There are no heat losses occuring at all.
4) The water was preheated.

Most transparent fluids are notoriously bad at retaining radiation heat gain. All kettles use a heating element because conduction and convection are the best ways to transfer heat to water.

Of course he could have just used another chemical that has a close to ambient temperature boiling point but there's still too many coincidences to allow it to occur based on radiation alone.

My point of contention is that 82W should not be burning things so quickly. If this were so, there would be a lot of melted lamps because even though the 100W light bulbs distribute the flow over a larger area, they are also exposed to them for a longer time. Some of the effects that he is showing have to be about 1000degC or higher on materials that have high thermal capacity. If the parabolic lens was, say, 5m in diameter or so then I would believe it.

I can't prove whether lasers were used or not but people have pulled more elaborate hoaxes before. Plus, the skeptic in me finds the destruction of the original device in a shed fire to be too coincidental (sorry about the Conspiracy Theories, Movie Bob).

1)Doesn't need to be 100%, and doesn't require 'blackbody' objects. Water doesn't absorb much visible light (about 25% in the first couple cms, to about 60% at the deep end of a pool), but it eats UV and IR (plus everything above/below it) at a massively higher rate.

2) Thermal conductivity coefficient of water is .6. This raises the rate of boiling that 1mL from 4s to 6.6s startging from 20 degrees C.

3) Heat loss? You do know how water releases heat, right? Steam's pretty good evidence that the water's releasing thermal heat through rapid evaporation.

4) If he'd been passing the thing through the light for a few seconds looking for the 'sweet spot', it's been heated above room temperature (my 20 degree C approximation)

Your lightbulb arguement conveniently ignores everything you have already brought up. The 'over time' involved in getting the same amount of wattage from a lightbulb to affect the same 1 sq cm of space is more than sufficient to allow for the thermal conductivity of the material and of air to distribute the energy. Also, light from a lightbulb does not contain the as full a spectrum that sunlight does, since it's concentrated more on the visible. Standard lightbulbs are terrible at heating things because of this, which is why you see special IR-heavy heating lamps used in restaurants to hold food at high temperature.

Alternately, what's your explaination for a 100W laser cutting through rock? Or a 50W laser used to cut plywood? They're just 50 and 100 watts?

It's fine to be skeptical, but are you actually doing any of the math involved, or just operating by 'feel'?

 

[reciprocal]

1)Doesn't need to be 100%, and doesn't require 'blackbody' objects. Water doesn't absorb much visible light (about 25% in the first couple cms, to about 60% at the deep end of a pool), but it eats UV and IR (plus everything above/below it) at a massively higher rate.

2) Thermal conductivity coefficient of water is .6. This raises the rate of boiling that 1mL from 4s to 6.6s startging from 20 degrees C.

3) Heat loss? You do know how water releases heat, right? Steam's pretty good evidence that the water's releasing thermal heat through rapid evaporation.

4) If he'd been passing the thing through the light for a few seconds looking for the 'sweet spot', it's been heated above room temperature (my 20 degree C approximation)

Your lightbulb arguement conveniently ignores everything you have already brought up. The 'over time' involved in getting the same amount of wattage from a lightbulb to affect the same 1 sq cm of space is more than sufficient to allow for the thermal conductivity of the material and of air to distribute the energy. Also, light from a lightbulb does not contain the as full a spectrum that sunlight does, since it's concentrated more on the visible. Standard lightbulbs are terrible at heating things because of this, which is why you see special IR-heavy heating lamps used in restaurants to hold food at high temperature.

Alternately, what's your explaination for a 100W laser cutting through rock? Or a 50W laser used to cut plywood? They're just 50 and 100 watts?

It's fine to be skeptical, but are you actually doing any of the math involved, or just operating by 'feel'?

1) Unfortunately I am not too familiar with the absorption of different electromagnetic bandwidths and how to calculate that in terms of the absorbed energy. I was basing my argument on the fundamental thermodynamics radiation equation, which uses the emissivity, absorptivity and the amount of area that receives the radiation. So how much of that 83W does the water actually absorb?

2) With natural convection, you need to use the density change as much as the thermal conduction coefficient and viscosity. From experience, a 20degC change in temperature is going to induce upward motion quite a bit. I find it hard to believe that you can induce that much of a local temperature increase unless the fluid is extremely viscous.

3) Asides from converting into a different phase, the water could lose the heat by radiating to the surrounding, conduction to the pliers and like (2) it could just naturally convect it. To flash immediately from water to steam means that it must be near the boiling point already.

4) Looking for a sweet spot would allow a whole lot of other things to occur during the mean time. The water doesn't just hang on to that heat in the mean time.

I will concede that the video itself and the timeframe doesn't allow me to make any educated calculations (not that I would want to put that much effort into proving / disproving a youtube video). It's just that I find it very hard to believe that something someone built out of their backyard without proper tools or materials is suddenly more efficient than an equivalent-sized solar collector using current-generation technology (not even including nanotech).

So I propose a "agree to disagree" ceasefire for the time being. When the kid gets accepted for his postgraduate degree and publishes his findings, I'd be real keen to read up on it. If I'm wrong then at least the solar energy driven eco-friendly world would be so much more efficient.

EDIT: Just thought I'd share a little something extra I hadn't considered before. A 600W microwave oven takes about 2 minutes to boil a cup of water. I sure hope the atmosphere does its job and keeps diffusing that microwave portion of 'light'!

 

[vansau]

1) Unfortunately I am not too familiar with the absorption of different electromagnetic bandwidths and how to calculate that in terms of the absorbed energy. I was basing my argument on the fundamental thermodynamics radiation equation, which uses the emissivity, absorptivity and the amount of area that receives the radiation. So how much of that 83W does the water actually absorb?

2) With natural convection, you need to use the density change as much as the thermal conduction coefficient and viscosity. From experience, a 20degC change in temperature is going to induce upward motion quite a bit. I find it hard to believe that you can induce that much of a local temperature increase unless the fluid is extremely viscous.

3) Asides from converting into a different phase, the water could lose the heat by radiating to the surrounding, conduction to the pliers and like (2) it could just naturally convect it. To flash immediately from water to steam means that it must be near the boiling point already.

4) Looking for a sweet spot would allow a whole lot of other things to occur during the mean time. The water doesn't just hang on to that heat in the mean time.

I will concede that the video itself and the timeframe doesn't allow me to make any educated calculations (not that I would want to put that much effort into proving / disproving a youtube video). It's just that I find it very hard to believe that something someone built out of their backyard without proper tools or materials is suddenly more efficient than an equivalent-sized solar collector using current-generation technology (not even including nanotech).

So I propose a "agree to disagree" ceasefire for the time being. When the kid gets accepted for his postgraduate degree and publishes his findings, I'd be real keen to read up on it. If I'm wrong then at least the solar energy driven eco-friendly world would be so much more efficient.

EDIT: Just thought I'd share a little something extra I hadn't considered before. A 600W microwave oven takes about 2 minutes to boil a cup of water. I sure hope the atmosphere does its job and keeps diffusing that microwave portion of 'light'!

1) You should be able to find the absorption graph for sunlight and water with a Google search. You'll likely get a lot outdoor swimming pool related sites, but as the topic is serious business to them you should be able to follow their links to the specific scientific papers or univesity sites. (Why don't I do it again? People believe and understand it more when they do their own work to get there.)

2) The coefficient already takes that into account. The 0.6 is a 'near enough' number - it varies from 0.56 to 0.58 at room temp, and then some more variance as the temp changes. This means that 1s after the 1mL of water is heated those 20 degrees, about 60% of the heat will disperse into adjacent water. Remember we're actually looking at 1 sq cm surface of water receiving the energy, which is less than 1mL (occupies 1 cu cm) which means a smaller portion of water is getting heated faster, then transferring that heat to the surrounding water. That small portion will reach localized boiling and convert to steam long before the rest; you can see this in any pot of water heated on a stove - steam begins to appear before the whole pot reaches boiling.

3) Radiating to it's surroundings brings into the equation the (hopefully Pyrex) glass test tube and then the air surrounding the test tube. The air isn't going to have much effect in the time frame provided (coefficient of about 0.024), and the thin glass test tube isn't as much of a 'heat sink' either.

4) Already covered in the above 3. It's a scale of time issue - normally 10-14mL of water will take a certain amount of time for sunlight to evaporate, but here it's speeded up by the amount that the light's concentrated. You can imagine it similar to spreading that same amount of water out over the same area and watching it evaporate.

As already linked by someone else in the thread, here's another example.

IEC 705 is the name of the standard for microwave power rating. I don't have the specifics of their actual testing procedure, but the below is a good approximation:

1 cup water is about 236mL. 4.184J to raise 1mL water 1 degree C. Room temp water estimated at 20 C, so we're raising it 80. Roughly 79000J of energy needed. Divide that by 120s, and you get 658, which is close enough to your IEC 705 rated 600W microwave.

Remember the microwaves coming off the magnetron are being scattered (HowStuffWorks.com used to have a nice diagram of the internals of a microwave, but I can't find it) to spread out over the contents below, so while you've got more power, it's spread out over a larger surface area. The concentrated sunlight in the video will acheive localized boiling fast, but take much longer to heat to a boil the same amount of water as the microwave.

edit: and I got sidetracked in looking for the IEC standard and microwave diagrams. Anyway, microwaves are absorbed rapidly by water, so the water vapor in the air strips a lot of the microwave radiation out before it hits the surface. Fat and muscle will absorb the rest. Microwaves are nonionizing (i.e. unlikely to cause cancer, unlike UV and other wavelengths) and the result of them striking your body is heat. Spend too long in the sun and you get a really deep burn (UV will cook your skin, microwaves can get below and cook the fat/muscle underneath).

 

[Iwana Humpalot]

What range does this thing have? Not long if i can tell, othervise those trees on the backround would have been burning.

 

[Mydnyght]

That was frickin' impressive. I don't know about you guys, but I wanna see the 23k version that the end of the video mentioned.