As temperatures rise across the globe, the demand for refrigeration and air conditioning units will continue to rise. And this in itself will exacerbate the crisis situation: the efficiency of modern cooling devices is not that high and they require a lot of energy, which leads to large emissions and exacerbates the greenhouse effect. Therefore, passive cooling systems are only welcome, and the new invention of scientists from MIT promises to increase their efficiency.
A group of scientists from the Massachusetts Institute of Technology developed perspective three-layer panel for passive cooling. The technology is claimed to reduce the panel temperature by up to 9.3°C compared to ambient temperature, even in humid climates. All that is needed for the operation of such a cooling panel is to add ordinary water to it. Quite a bit of water. For hot and arid climates, this will have to be done more often – once every four days, and for regions with high humidity, it will be enough to add water once a month.
The installation resembles a solar panel. Its top layer is an airgel – a porous vapor-permeable plastic structure with pores filled with ordinary air. Under the airgel is a layer of hydrogel – also a layer of polymer, but with water in the pores. This layer is in many ways similar to hydrogel medical dressings for treating open wounds. The third – the lowest layer – is a mirror surface that reflects the sun’s rays back, which prevents the object being cooled behind the panel from heating up.
The researchers emphasized that for the first time they combined long-known principles in one solution – this is cooling by the method of liquid evaporation and radiative cooling, when infrared radiation from an object (heat) goes into space, and does not dissipate in the surrounding space. On this principle, already proposed a range of cooling systems that can even keep solar panels running at night. Also, an interesting solution was the use of an airgel layer as thermal insulation, which additionally protected the cooled object from heating by the sun’s rays.
The sandwich panel works as follows. The airgel transmits infrared radiation to the hydrogel layer, but cuts off all other rays of the sun. Infrared radiation vaporizes the water in the hydrogel layer and the vapor escapes through the airgel. Excess infrared radiation and the panel’s own infrared radiation are radiated into space. Consumable material in such a scheme is ordinary water. The prototype showed record-breaking panel efficiency, providing a difference between the ambient temperature and the panel up to 9.3 °C.
The proposed solution can be suitable for both houses and containers for the transportation and storage of food in regions where there are no stable sources of electrical energy. Covers of food pavilions can be equipped with similar panels. In humid climates, this will help extend the shelf life of perishables by up to 40% and up to three times in drier conditions (where the temperature difference between refrigeration and air will be greater).
The only barrier to the commercialization of the development remains airgel, whose production is still inefficient. Today, it is produced only in laboratory conditions in the process of mixing polymer and solvent and extremely long subsequent drying. Scientists promise to develop a technology for simplified production of airgel, and then passive refrigerators and passive “boosters” for air conditioners can become widespread.
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