Heat Transfer Enhancement on Surface Modified via Additive Manufacturing during Pool Boiling of Freon

This article presents the results of experimental studies of the efficiency of heat transfer on a flat rectangular ( 16× 24 mm 2 ) heat transfer surface ( HTS ) modified via additive manufacturing. Comparative experimental studies were carried out on an unmodified HTS and two modified HTSes with different geometric parameters of the modifying coating. A porous sinusoidal coating consisting of spherical bronze granules with an average diameter of 35 μ m was 3D printed on the brass base of the heat transfer unit. The coating thickness is 150 μ m in the deepenings and 300 μ m and 700 μ m on the ridges. The heat transfer was studied during free-convection boiling of liquid freon R21 at heat flux densities of 200– 5· 10^5 W/m 2 at a reduced pressure of 0.03. The experiments have shown that for the modified surfaces, activation of nucleation sites begins at a significantly lower heat flux density compared with the case of the smooth unmodified surface. Under conditions of activated nucleation sites on a modified surface, the heat transfer coefficient increases 4–5 times. Activation of nucleation sites is realized in the deepenings of the sinusoidal coating. Upon activation of nucleation sites (at heat loads less than 100,000 W/m 2 ), the heat transfer intensity is the same for both studied surfaces having the same coating thickness in the deepenings. On the surface with significantly higher ridges at heat loads 10,000 < q< 300,000 W/m 2 upon activation of nucleation sites, the temperature difference observed is smaller than that on the surface with smaller ridges.