Because their energy is lower than that of red light, these wavelengths are called infrared. To study the new concept, Chen's team built an object they would try to cool. They used mostly silicon. The basic ingredient in beach sand, silicon is both cheap and sturdy.
ISBN 13: 9781490495057
The base of their object was a super-thin disk of silicon, about twice the thickness of a human hair. That layer was for structural support. To that, they added a thin layer of aluminum. It reflected light waves like the shiny layer on the back of a glass mirror. Next, the researchers added the layer of material they wanted to cool. It, too, was made of silicon, but was much thinner than the base layer. It was just nanometers — billionths of a meter — thick. The researchers chose that material because it mostly emits radiation in the 8- to micrometer wavelength range.
Another way is conduction. It happens as atoms move around and bump into one another. During this natural jostling, warmer atoms transfer some of their energy — heat — to colder atoms. To minimize energy transfer through conduction, Chen and his team built a special chamber to hold their disk. Inside, they placed the disk on top of four small ceramic pegs.
The result was kind of like a tiny table. Ceramics do not transmit heat well. So with this design, very little heat could move from the disk to the chamber floor through conduction.
The researchers also wanted to minimize heat loss through convection. That meant minimizing the radiation that could reach it from the outside. First, they made the upper surface of the chamber the one pointed toward space from a special material: zinc selenide. This material only lets in radiation between the wavelengths of 8 and 13 micrometers.
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The team also designed a special panel that blocked sunlight and kept the chamber in the shade during tests. They also put a cone of reflective material around the top of the chamber. The team tested its device on the roof of their building at Stanford.
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Some of those tests spanned a full 24 hours. The object's heat energy successfully disappeared into space. But the cooling indeed was efficient when the humidity was low. For one thing, the object the team cooled is small and specially designed. But it could help out other types of cooling systems, Minnich suggests. That extra help might be a little bulky, though.
For one thing, he notes, to radiate energy at the same rate as a watt light bulb, engineers would need to build a surface of about 1 square meter And sometimes engineers have problems making experimental devices work when they try to enlarge them. Sucking all the air out of a larger chamber without making its walls crumple is tricky. In particular, zinc selenide the material the team used as the top of their cooling device is quite expensive. But with further research, he says, engineers might find a cheaper substitute.
It is light and soft, and used in many items from bicycles to spacecraft. Atoms are made up of a dense nucleus that contains positively charged protons and neutrally charged neutrons. The nucleus is orbited by a cloud of negatively charged electrons. Bricks, porcelain and other types of earthenware are examples of ceramics. Many high-performance ceramics are used in industry where materials must withstand harsh conditions. The other two are convection and radiation. In conduction, energy is transferred when atoms and molecules bump into each other, with slower, colder particles gaining energy from the warmer, faster ones that slam into them.
This process occurs in the outer layers of some stars. Electromagnetic radiation is typically classified by its wavelength. The spectrum of electromagnetic radiation ranges from radio waves to gamma rays. It also includes microwaves and visible light. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need. Air with a lot of water vapor in it is known as humid.
Other invisible wavelengths include X rays, radio waves and microwaves. It tends to record a heat signature of an object or environment. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms O 2 , but water is made of two hydrogen atoms and one oxygen atom H 2 O. The other two are conduction and convection.
In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space. Pure silicon exists in a shiny, dark-gray crystalline form and as a shapeless powder. Laboratories or manufacturing plants may use vacuum equipment to pump out air, creating an area known as a vacuum chamber.
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Cover Photo by Linda Myers. Telepathic dreamer Sarah Stevens worked for fourteen years to build the courage to leave her cruel husband Dietrich Peters, and four more years to build a life for her and her two teenage sons in steamy Baton Rouge, Louisiana. Just as Sarah meets a good man she could fall in love with in a heartbeat, Dietrich barges back into her life, and Sarah is not about to put up with it.
But Dietrich will not be deterred. He invades her home, her dreams, her mind, and he grows more threatening with each passing hour.