Studies of the heat transfer coefficient and thermal resistance for a loop thermosiphon with a high heat flux density in the transport zone, as well as studies of the critical heat flux using a traditional thermosiphon, have been carried out. Measurements were carried out for pure water, water with porous coatings of the vaporization surface and nanofluid, all other things being equal, using technically polished copper surfaces as the boiling surface. The mechanism of formation of nanorelief on the vapor-generating surfaces of thermosyphons and an increase in the heat transfer coefficient and critical heat flux due to this is revealed. A dynamic model of the formation of this nanorelief is proposed. Accelerated and long-term life-test of a loop thermosiphon filled with water with iron oxide and copper oxide nanoparticles were carried out, and its stable performance was shown.