Experimental studies of heat transfer during pool boiling on a modified surface and flow boiling in a modified minichannel at high reduced pressures were carried out. The relevance of these studies is associated with the growing interest in miniature heat exchange devices, used in various industries, and in enhancing the boiling heat transfer. It is possible to provide the required heat flux density using phase transitions of the coolant and additional intensification of heat transfer. The surface modification for pool boiling and flow boiling in minichannel was performed by processing with laser impulses. Modification of the inner wall of the minichannel was carried out using the action of a laser impulse on the outer surface of the channel.

This work presents a description of two experimental setups, as well as experimental data on heat transfer. Experiments in a vertical smooth and modified channel with a diameter of 1.1 mm and a length of 50 mm were carried out with R125 under conditions of reduced pressures p/p_cr≅ 0.43 and 0.56. The mass flow rate varied in the range G = 200 ÷ 1400 kg/m²s. The temperature of the flow at the inlet to the working section was kept constant, close to room temperature. The maximum heat flux was limited by the critical heat flux. Experimental studies of heat transfer and critical heat flux (CHF) during pool boiling were carried out on dielectric liquids R113, RC318 and Novec7100 in the saturation state in the range of reduced pressures p/p_cr≅ 0.03−0.36. It was obtained the values of CHF for boiling on the modified surface.

The greatest effect of the modification on the heat transfer in the minichannel is observed at p_r=0.43 for the mass flow rate G = 800 kg/(m²s), heat transfer coefficient (HTC) increased up to 65%. The results obtained at reduced pressure p_r=0.56 show a lower degree of intensification, up to 44%. Twenty-two values of CHF during pool boiling were obtained on a modified surface and compared with calculation for a smooth surface.