B The principle of operation and application of optical lenses

[Anatoly Anatoly]

I am interested in the principle of operation and application of optical lenses. In particular, how does the distance of the optical lens from the object affect the temperature of its heating? To what maximum temperature can an object be heated? Which object is more efficient to heat? At what distance can a beam be focused? Can several lenses be used to focus a beam at large distances?

 

[berkeman]

welcome to PF.

What do you know already about lenses and lens systems?

https://en.wikipedia.org/wiki/Lens

By "heating", I'm guessing you are focusing the rays of the Sun?

 

[sophiecentaur]

By "heating", I'm guessing you are focusing the rays of the Sun?

I guess the same.
Perhaps the OP should look at this wiki entry. There are several factors involved in solar furnace design.

 

[Anatoly Anatoly]

Thank you very much for the answer and link to the Wikipedia article. On Wikipedia, the main reason why CSP is not used is non-competitiveness (solar panels are more profitable). I don't understand how a lens (eternal) can lose to a solar battery, the service life of which is 25-30 years. Imagine a situation when, after a global catastrophe, humanity will not be able to produce complex technological devices. On the other hand, the lens was used by Archimedes thousands of years ago. Do you think lenses can be used in the household

 

[weirdoguy]

a lens (eternal)

How can lens be eternal? Nothing is eternal. Well, maybe Cher is, but that's another conversation.

 

[Andy Resnick]

On the other hand, the lens was used by Archimedes thousands of years ago.

I'll probably regret jumping in to this, but Archimedes did not use a lens. I believe the first mention of lenses was China around 150 BC, specifically lenses made from ice that were used to start fires:

https://www.epsnews.eu/2015/10/opti...ient,the world's first surveillance periscope.

 

[Anatoly Anatoly]

Good afternoon. If anyone has any information, please let me know. Is there any CSP installation suitable for domestic use.
Heating a swimming pool, a room, heating a greenhouse or a house.

 

[berkeman]

Good afternoon. If anyone has any information, please let me know. Is there any CSP installation suitable for domestic use.
Heating a swimming pool, a room, heating a greenhouse or a house.

What's CSP? Concentrated Solar Power maybe? Are you familar with Heliostats? They are more efficient than using lenses...

https://en.wikipedia.org/wiki/Heliostat

https://media.istockphoto.com/id/12...=X81wdNR1KyMEfQ8SSLr-NsapdTHnYZeSSCimFCZBw0k=

 

[Anatoly Anatoly]

Can lens energy be used in the home?
Cook dinner
Heat water
Heat a house

 

[renormalize]

Can lens energy be used in the home?
Cook dinner
Heat water
Heat a house

Specify your power requirements for each and then see how big your lens would have to be. For example, a stovetop coil element consumes about $2\text{ kW}$ of electricity to heat a pot of water. Sunlight delivers roughly $1\text{ kW}/\text{m}^2$ at the earth's surface, so you'd need a round lens at of at least $2 \text{ m}^2$ in area, or $1.6 \text{ m}=63 \text{ in}$ in diameter, to boil water as fast as an electric stove does (assuming 100% efficiency of converting sunlight to heat).

 

[sophiecentaur]

Do you think lenses can be used in the household

I'd say that extreme CSP is not the way to go for domestic solar energy. Hundreds or thousands of degrees doesn't really have an application in the home and it is expensive!!

The reason for using a lens (or a reflector) is to concentrate the incident energy from the sun. The most relevant factor is the collecting area and a lens of more than,say 200mm would be heavy and expensive. A shiny reflector of a couple of metres diameter would gather [ten Sorry - a hundred ] times as much energy. Also, unless you want to heat a small region to a very high temperature you are better off using a cheaper, safer and less stringent method by de-focussing the image and spreading the heat over a wider area to avoid actually useful temperatures. In many applications, avoiding actual boiling would be most convenient.
For "cooking dinner", you could go to 210C with a more concentrated beam (by sharpening the focus using the same reflector.
For heating the house you would need several kW worth of power and that would require an area of several metres squared and a different technology. There would seldom be a need to 'concentrate' the heat so flat panels are the best solution for the home.

 

[wells_c]

"a lens of more than,say 200mm would be heavy and expensive."
Rear projection televisions contain a fresnel lens as part of the screen that are roughly a meter squared in area, and are capable of concentrating the sunlight hitting it to a spot roughly 4 square centimeters. I've used one to melt black beach sand, or magnetite. Wikipedia lists it's melting point at just shy of 1600 deg. C, which sounds about right for a kilowatt going into a spot that size.

 

[TensorCalculus]

This might not be directly answering your question, but I hope it helps:
It doesn't just depend on the lens, but also on the light you use. There's something called conservation of étendue.
Étendue is (basically) the area of a light beam multiplied by the angle it subtends (hopefully the diagram I pulled off the internet helps somewhat to explain this - S is the area and alpha the angle). This is a conserved quantity - which basically means you can't make a beam narrower without increasing it's angular spread, or losing intensity, or vice versa.
It's something that is often into account when designing things that require lenses or other ways of manipulating light, as it means that you're not just limited by the lens but in a lot of cases by the light source too - you can't just infinitely "squeeze" or narrow a beam without losing intensity.

It's not a direct answer, but I do hope it helps to satisfy your curiosity! (Do take all of this with a pinch of salt though because I am just a student as well and certainly not an expert)

 

[phyzguy]

Can lens energy be used in the home?
Cook dinner
Heat water
Heat a house

Of course. Here is a picture of a solar oven. Many homes have solar hot water heaters on the roof. Many homes also have passive solar heating. South and west facing windows can go a long way to heating your house. These are not using lenses because no lenses are needed. In cases requiring focusing a mirror is almost always better than a lens.

 

[sophiecentaur]

Many homes have solar hot water heaters on the roof.

I've seen many flat panels (full of water) but there's no focussing involved. Heating water to 60C, doesn't require a small spot and it's a lot cheaper