The essence of solar engineering split flat solar collector water mist

Time: 2019-01-19
Water fog is the most intuitive impression of the solar collectors, and it is also the most troublesome thing for solar collectors. In fact, the water mist is only a representation. The essence of its existence is that there is water in the cavity of the solar energy collector, and it will not disappear due to the evaporation of sunlight.

To analyze these moistures, there are three sources:

Residual moisture: The material in the heat collecting chamber (especially the heat insulating material) is brought into the cavity when it is encapsulated due to the balance with the environmental humidity. In the humid area (such as China's Guangdong and Guangxi and Jiangsu and Zhejiang), this residue There will be more water, and in dry areas (such as Northwest China and Inner Mongolia) it will be better.

Infiltration of moisture: Moisture that is infiltrated by the outside due to the non-sealing of the heat collecting chamber, such as rain, especially during violent storms.

Moisture-reducing moisture: In the humid environment, the moisture generated by the moisture absorption of the internal material formed by the difference in humidity between the inside and the outside (the external humidity is large and the internal humidity is small) is actually an equilibrium moisture formed by balancing the humidity.

Hazard of moisture in flat collector

Attenuation of solar radiation: the water in the cavity evaporates and condenses into a water mist on the transparent cover (glass) of the flat collector, the transmittance is affected, and the received solar radiation energy is weakened and increased. Convective heat loss from the top air interlayer.

Adiabatic and damp: The thermal insulation material is mostly porous and easy to absorb moisture. The thermal conductivity of water is 25 times that of air, and the thermal conductivity of ice is greater. After the moisture absorption of the material, the moisture content occupied a part of the pore space which was originally filled with air. Studies have shown that the thermal insulation coefficient of 0.03 W/M·K is increased by 25% after the absorption of 1% moisture, and will increase exponentially.

Absorption surface degradation: Studies have shown that the absorption surface will produce different degrees of corrosion in the salt spray experiment, and the ability of different absorption surfaces to resist salt spray test is also different. The high quality black chromium coating can withstand 120 hours, and the radiation characteristics are special. A good blue titanium coating is even only 6 hours; as a non-professional user, there are also observations and experiences that are directly used by the user. Some companies produce blue-film balcony flat-plate collectors in Inner Mongolia for a winter after the discovery of white spots on the absorption surface.

The phenomenon of water fog and the problems it brings are serious. This is the result of the superposition of external and internal factors. The external cause is the environment, the rain, the storm, the temperature and humidity, the harmful substances in the atmosphere, especially PM2.5. And the invasion of fine dust makes the interior of the flat collector cavity become the object of acid-base salt spray invasion to different extents; the internal cause should be sought from the structure and material of the flat collector. Flat panel collectors are one of the leading products in the field of solar energy. The appearance of water mist has seriously affected the thermal performance and life of flat panel collectors.

Finally, it was found that the main factors affecting the water mist were three aspects: the moisture absorption of the insulation material was too large, the product was not tightly sealed, and the exhaust effect was poor. These problems also require industry experts and manufacturers to overcome the technical difficulties, better solve the water mist and corrosion problems of flat panel collectors, and produce high-quality flat-panel solar products to give back to the vast number of users.

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