A cooling device comprises a cooling tube containing a working gas, a pressure oscillator connected to a first end of the cooling tube to generate a pressure oscillation and displacement of the working gas, and means for phase shifting the pressure oscillation relative to displacement of the working gas, connected to a second end of the cooling tube. The device further comprises a first sealed pressure transmission element to separate the working gas from a fluid contained in the phase shifting means. The fluid and the working gas are of different natures.