▎ 摘　　要

NOVELTY - Solar heat collecting device comprises a reflecting mirror, a heat collecting pipe box (8), an upper pipe (2), and a heat releasing pipe group (1). The heat releasing pipe group contains a left heat releasing pipe group (11) and a right heat releasing pipe group (12). The left heat releasing pipe group is connected with the upper pipe and the heat collecting pipe box. The right heat releasing pipe group is connected with the upper pipe and the collector pipe box so that the heat collection pipe box, upper pipe and heat releasing pipe group form a closed circulation of heating fluid. The heat-collecting pipe box is filled with phase-change fluid. USE - Solar heat collecting device used in solar heat collector (claimed). ADVANTAGE - The device can realize vibration and descaling of a heat collecting device. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (1) a method for treating sewage by solar energy, which involves using water tank and light-to-heat conversion element; floating light-to-heat conversion element in sewage in upper portion of water tank; introducing steam into cooling coil for cooling; using heat released by steam condensation to preheat water in hot water tank; condensing steam in the cooling coil into water, and introducing water into recovery device; (2) a method for preparing a photothermal conversion element, which involves synthesizing reduced graphene oxide by adding 1000-3000mg graphene oxide to 1000-3000mL deionized water, adding 750-9000mg ascorbic acid to obtain a graphene dispersion, reacting it in microwave reactor to remove impurity in upper layer of the suspension, filtering it with suction, rinsing it with ultrapure water for three times, freezing and vacuum drying the sample to obtain reduced graphene oxide powder; preparing photothermal conversion device by dispersing 1g of reduced graphene oxide into 1000ml of mixed solution of water and ethanol by ultrasonic treatment, adding agarose and urea to solution, stirring it to obtain hot suspension, smearing suspension on surface of foamed nickel, and cooling foamed nickel substrate with reduced graphene oxide coating naturally, and freeze-drying in refrigerator for 12 hours before taking it out; and preparing substrate; (3) a solar heat collector; and (4) a solar thermal collection sewage water intake device. DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of solar heat collecting device. Heat releasing pipe group (1) Upper pipe (2) Heat collecting pipe box (8) Left heat releasing pipe group (11) Right heat releasing pipe group (12)