... the alternative absorption coating on the inner surface of the vacuum tube, from the high-temperature environment super-conduction tubes, ... to absorb the solar energy, heat the water in the vacuum tube directly, through the cold hot water convection, changes ... Dia≤25mmHeat pipe anti-freezing ≥-35°C Life span Approximate to 15 years Model NO.Glass vacuum tube specificationDiaLengthNumber(mm)(mm ...