Credit: scienceblog.com

It’s claimed this invention could be used to improve any type of cooling system.

Imagine a device that can sit outside under blazing sunlight on a clear day, and without using any power cool things down by more than 23 degrees Fahrenheit (13 degrees Celsius).

It almost sounds like magic, but a new system designed by researchers at MIT and in Chile can do exactly that says TechXplore.

The device, which has no moving parts, works by a process called radiative cooling.

It blocks incoming sunlight to keep from heating it up, and at the same time efficiently radiates infrared light—which is essentially heat—that passes straight out into the sky and into space, cooling the device significantly below the ambient air temperature.

The key to the functioning of this simple, inexpensive system is a special kind of insulation, made of a polyethylene foam called an aerogel.

This lightweight material, which looks and feels a bit like marshmallow, blocks and reflects the visible rays of sunlight so that they don’t penetrate through it. But it’s highly transparent to the infrared rays that carry heat, allowing them to pass freely outward.

The new system is described today in a paper in the journal Science Advances, by MIT graduate student Arny Leroy, professor of mechanical engineering and department head Evelyn Wang, and seven others at MIT and at the Pontifical Catholic University of Chile.

Such a system could be used, for example, as a way to keep vegetables and fruit from spoiling, potentially doubling the time the produce could remain fresh, in remote places where reliable power for refrigeration is not available, Leroy explains.

Minimizing heat gain

Radiative cooling is simply the main process that most hot objects use to cool down. They emit midrange infrared radiation, which carries the heat energy from the object straight off into space because air is highly transparent to infrared light.

The new device is based on a concept that Wang and others demonstrated a year ago, which also used radiative cooling but employed a physical barrier, a narrow strip of metal, to shade the device from direct sunlight to prevent it from heating up. That device worked, but it provided less than half the amount of cooling power that the new system achieves because of its highly efficient insulating layer.

“The big problem was insulation,” Leroy explains. The biggest input of heat preventing the earlier device from achieving deeper cooling was from the heat of the surrounding air. “How do you keep the surface cold while still allowing it to radiate?” he wondered.

The problem is that almost all insulating materials are also very good at blocking infrared light and so would interfere with the radiative cooling effect.

Continued here.

via Tallbloke’s Talkshop

https://ift.tt/324gDP8

October 31, 2019 at 02:34PM