NOVELTY - Preparation of copper nanofluid solar cooling liquid comprises dissolving phosphate in deionized water to obtain phosphate solution; dissolving benzotriazole in ethylene glycol and propylene glycol to obtain alcohol solution; adding nano copper powder into alcohol solution; dispersing for 3-8 minutes; adding vinylpyridine and azobisisobutyronitrile; further dispersing for 4-7 minutes; putting mixture into flask at 80-90 degrees C for 2-4 hours; cooling at room temperature to obtain nano copper suspension; and mixing phosphate aqueous solution and nano copper suspension.    USE - Preparation of copper nanofluid solar cooling liquid.    ADVANTAGE - The method produces copper nanofluid solar cooling liquid with thermal conductivity that is four times higher than that of deionized water, has good dispersing uniformity, has excellent stability after standing for 2400 hours at normal state, has low freezing point without occurrence of icing at - 40 degrees C, has excellent corrosion resistance, and is suitable for anti-freezing liquid. It has wide, cheap and easy to obtain material sources, has low equipment requirement, and is suitable for large scale production.    DETAILED DESCRIPTION - Preparation of copper nanofluid solar cooling liquid comprises dissolving phosphate in deionized water via PTFE electric mixer to obtain phosphate solution; dissolving benzotriazole in ethylene glycol and propylene glycol to obtain alcohol solution without generating bubble; adding nano copper powder into alcohol solution; high speed dispersing for 3-8 minutes; adding vinylpyridine and azobisisobutyronitrile; further dispersing for 4-7 minutes; putting mixture into flask fixed on electric heating sleeve; controlling temperature at 80-90 degrees C; maintaining reaction for 2-4 hours; cooling at room temperature to obtain nano copper suspension; mixing phosphate aqueous solution and nano copper suspension via middle-speed stirring to obtain transparent and colorless solution; adding amide-based dispersant; completely dissolving to obtain nano copper mixed solution; subjecting nano copper mixed solution into ultrasonic vibration for 1-4 hours to obtain crude copper nanofluid; putting nanofluid into variable-diameter pipe system; and starting circulating pump to make thick copper fluid circulates through folding reducer pipe for 1-7 hours to obtain nanofluid solar cooling liquid.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of variable-diameter pipe system.