Abstract: Disclosed is a flash closed heat exchanger, comprising a closed housing. A negative pressure fan is provided on the closed housing. A negative pressure environment is formed inside the closed housing by means of the negative pressure fan. A water atomization device is provided inside the closed housing. The water atomization device sprays atomized water into the inside of the closed housing, so that the atomized water evaporates into steam in the negative pressure environment. In the flash closed heat exchanger, the evaporation of atomized water is promoted in a closed negative pressure environment.