The film structure is different, resulting in a different principle of absorbing the sun's rays. The graded film is a multilayer film, and its absorption layer is generally 9 layers. It absorbs sunlight layer by layer, and its ability to absorb light gradually becomes higher.
Due to this gradual structure, the emission ratio increases continuously with the rise of temperature, so that when the working temperature is 300~500℃, the emission ratio increases greatly. In addition, the aluminum ions in the absorption layer are greatly enhanced in activity and drift under high temperature conditions. In this way, the internal structure of the film layer is disordered, causing the film layer to begin to age. In such a high temperature state for a long time, the film will fall off, which affects the heat collection efficiency and life of the vacuum tube.
The interference film has two absorption layers. Between the two films, interference occurs due to the different proportions of metal components, which increases the absorption ratio and reduces the emission ratio. Coupled with the anti-reflection layer to reduce the reflection, so as to achieve a higher absorption ratio and lower emission ratio, greatly improving the heat collection efficiency.
