Biomimicry and thermo-regulation: playing with temperatures, a natural game
Thermo-regulation concerns all sectors of activity. Whether it is about making a place comfortable for living beings or ensuring the proper functioning of a technical system, temperature is often an important parameter. Thus, a building or a means of transport must remain within reasonable temperature ranges, an electronic system must not overheat for safety reasons. Likewise, a chemical or medical component, such as a vaccine, must be maintained at a temperature guaranteeing its effectiveness.
To control temperature in such diverse conditions, many challenges arise.
First of all, questions of thermal insulation are essential to achieve a constant temperature regardless of external conditions, whether it is keeping a place hot or cold. This is generally not sufficient, and heating or cooling mechanisms are also necessary. The less energy these mechanisms consume, the better, both from an economic and environmental point of view.
Finally, when processes generate heat, we must be able to dissipate this heat efficiently. Thermo-regulation issues are therefore complex and varied, and progress in this area is necessary for many applications.
A specialist in the field, Bioxegy explains to you through a few examples why and how biomimicry is a source of solutions and new approaches for thinking about the thermo-regulation systems of the future.
Nature does not escape the need for thermoregulation.
On the contrary, the chemical reactions necessary for life, and more particularly the metabolisms of each living being, are effective in restricted temperature ranges, while external temperatures, in the air or in the water, vary enormously within of a day, a year, or even geographically.
It's not for nothing that migratory birds fly to warmer regions in winter! Animals that winter or hibernate have chosen another strategy against the cold: since it makes them less efficient, they work less. Many other mechanisms are implemented by all species to adapt their temperature, as always in nature, in the most energy-efficient way possible.
Thus, furs or plumages insulate the animals that wear them, transpiration cools plants and animals alike, and nests or burrows provide protection against external temperatures.
Finally, behaviors, individual or collective, also play an essential role in animal thermoregulation.
Reflecting the Sun so as not to heat up: the Sahara ants' thermoregulation
Silver ants live in the Sahara Desert. They must protect themselves from the arid conditions that reign there: their body temperature must remain between 48°C and 51°C, while under the sun the ground temperature can exceed 70°C!
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Unlike many hot desert species, their strategy is not to live at night and hide during the day. How do they survive in such temperatures? Their hair offers them great protection. Thanks to their triangular shape, they reflect the majority of solar radiation received, which limits the heat provided by the Sun. The reflection is what gives them their pretty silver colour!
In addition, the microstructure of these hairs allows good emissivity of infrared radiation, which effectively cools the ant.
The structure of Sahara ant hairs has been reproduced to provide a surface with cooling properties. This new surface reflects more than 97% of solar radiation, which greatly limits its warming.
In addition, the structure, like that of the silver ant's hairs, improves the emissivity of the surface: it therefore cools more effectively by radiation. The cooling power obtained is the highest to date for a microstructure, opening up interesting thermoregulation possibilities, whether it be for buildings or even satellites.
Insulate like polar bear fur
Polar bears are subjected to very low temperatures, as low as -40°C! Nevertheless, homeothermic animals manage to maintain a constant internal temperature in summer and winter.
To help them do this, their fur is a great support: composed of numerous porous hairs, it creates an important barrier between the bear and the outside world. In fact, the air trapped in the hairs conducts very little heat (this is what is used in double glazing!). In this way, the temperature difference between the exterior of the fur, which remains very cold, and the interior, which must remain warm, is exacerbated.
The polar bear's surface then emits little infrared, which limits the animal's loss of heat through radiation.
An insulating textile has been developped using this structure. Made up of porous fibers, this textile is both light, resistant and thermally insulating. It thus makes it possible, like polar bear fur, to both maintain a temperature difference between the outside and the inside and to limit the emission of thermal radiation. Among other applications, it can then serve as an invisibility cloak for an infrared camera!
A heat exchanger inspired by the human vascular system
The human vascular system allows the transport within the body of nutrients for nutrition and gases for respiration.
What is less known is that it also plays a role in our thermoregulation. Indeed, the exchange of matter is accompanied by heat exchanges, in order to keep the central temperature at 37°C no matter the external conditions. The hierarchical organisation of the blood vessel network, whose veins and arteries separate into increasingly numerous and small capillaries, allows efficient material and thermal exchanges.
Microelectronic systems require effective thermoregulation in order not to overheat. The size of the components, increasingly smaller, requires that the efficiency of thermo-regulation systems be further improved. To do this, why not take inspiration from our own thermo-regulation? Thus, an algorithm making it possible to optimise the size and organisation of the channels of a heat exchanger was developed taking inspiration from the vascular system. The arrangement obtained makes it possible, in the tested case, to reduce the maximum temperature by 24°C compared to a classic organisation of parallel channels.
Other promising prospects for biomimicry in industrial sectors
