Water vapor phase change energy-saving apparatus

The invention provides a water vapor phase change energy-saving apparatus capable of reducing vaporization potential heat value under power station boiler and industrial boiler water supply system. The energy-saving apparatus comprises a water inlet, a water outlet, a shell, a magnetization unit and a magnetization unit fixing device; the magnetization unit has multiple groups which are fixed by the magnetization unit fixing device and tightly arranged along the axial direction of a water-supply-pipe; the magnetization unit and the magnetization unit fixing device occupy the pipe space besides the water inlet and the water outlet; the magnetization unit comprises multiple groups of paired rare earth permanent magnets; and the any adjacent two groups of magnetization units are fixed on the pipeline cross section with wide angle of rotation angle.