Effect of Modification of Heat-Release Surface on Heat Transfer in Nucleate Boiling at Free Convection of Freon

This paper presents experimental results on heat transfer efficiency on a flat circular heat-release surface modified using additive technology. A porous plate 500  $$\mu$$ m thick, 3D-printed from copper spherical granules with an average diameter of 50  $$\mu$$ m, was fixed by means of resistance soldering on a heat-release brass surface of 20 mm in diameter. The heat transfer was investigated at boiling in liquid Freon R21 under free convection conditions for the heat flux density varying from 200 to $$4.5\cdot 10^{5}$$  W/m2. In different series of the experiments, the reduced pressure varied within 0.027–0.064. The experiments have shown that under conditions of activated nucleation sites, the heat transfer coefficient for a modified surface 4–5 times exceeds that for an unmodified surface. The greatest effect is observed in the region of small and medium values of the heat flux density.