Aerogels have been widely used due to their characteristics. For example, nano sized pores in aerogels can collect various pollutants like sponges. Bob, a Nottingham native in England, has a house insulated with aerogel, and the heat preservation effect of the house has been greatly improved. Mountaineers wearing hiking boots with air gel thermal insulation insoles only feel the soles of their feet are too hot when climbing Mount Everest. Aerogel can also be used as catalyst carrier, super adiabatic combustion carrier, combustion substance (similar to solid alcohol) that can be used in severe weather conditions, combination with fuel cell technology, and photocatalyst carrier.
1、 Three pathways of heat conduction
Macroscopically speaking, the essence of heat is the external manifestation of the irregular motion of a large number of molecules. The hotter an object is, the more intense its molecular motion is. This movement is manifested as the free movement of gas molecules in gas; In liquid, it manifests as the clustered flow of liquid molecules; In solids, it manifests as the vibration of solid molecules at a certain position. In summary, there are three ways to conduct heat, namely: thermal conduction, convection, and radiation.
Thermal conduction is generated due to the mutual influence of thermal vibrations of object molecules, and its tendency is to make the heat of the entire object uniform everywhere.
Convective heat conduction is caused by the relative flow of hot and cold liquids due to the low density of hot gases or liquids under the action of gravity.
Radiant heat conduction is a way of conducting heat outward in the form of electromagnetic waves, which is present in all objects with temperatures above absolute zero. In order to achieve good insulation effect, insulation materials must suppress the three thermal conduction pathways mentioned above.
2、 Analysis of Material Thermal Insulation Principle
Porous silica aerogel composite thermal insulation material developed by AISION can well inhibit the above three heat conduction paths.
The size of solid thermal conductivity, from the perspective of insulation materials, is only related to the inherent thermal conductivity of the material itself and its density. In order to reduce the density of materials, most insulation materials adopt the method of creating pores. The porous silica aerogel gel composite thermal insulation material developed by our company has reached the acme in this regard; The porosity of this material accounts for over 90% of the total volume, resulting in an extremely low material density, only about a quarter of that of water.
However, because most insulation materials contain a large number of pores, the convective heat conduction of the gas contained inside the pores becomes a key heat conduction pathway. According to research, convective heat conduction is only related to gas properties and pore size. Different insulation materials use different methods to reduce convective heat conduction of materials. For example, polyurethane foam material is filled with Freon gas in the pores, which has a thermal conductivity only one-third of that of air, thus achieving superior insulation performance. However, due to its ability to seriously destroy the ozone layer, it has been replaced by carbon dioxide and other materials. However, carbon dioxide and other materials used as fillers in polyurethane also have the problem of high thermal conductivity. This material adopts another approach, which is to reduce the pore diameter to lower the thermal conductivity of air in the pores. The material is made through special processes, with an average pore diameter of only 50-60 nanometers, which is about one thousandth of the diameter of a hair, while the average free path of air molecules is around 70 nanometers. In such a small gap, air can hardly flow, thereby suppressing convective heat conduction of air.