Use of Dispersed Flow for Cooling a Surface Modified by an Electrical Erosion Method

Abstract

The results of activities on studying the cooling of high-temperature surfaces and phase change heat transfer enhancement are briefly analyzed. A set of works aimed at modernizing the experimental setup intended to model thermally stressed components of power installations is carried out. The heat transfer process that takes place in the cases of applying hydraulic and pneumatic atomizers has been studied on the setup. A technique for modifying a surface using the electronic erosion method is proposed and described. Two new heat transfer surfaces of a test section were fabricated using the new method, and their macrophotographs and roughness profiles have been obtained by means of a microscope and contact profilometer. The efficiency with which the modified and nonmodified surfaces are thermally stabilized by a dispersed flow at coolant flowrates equal to 2.1 × 10^–3 and 4.3 × 10^–3 kg/s using hydraulic and pneumatic atomizers was experimentally studied. The dependences of heat flux on the cooled surface temperature were analyzed. It is shown that the heat flux removed from the modified surface cooled with liquid sprayed by the hydraulic atomizer is by 20–50% higher (its value increases with increasing the coolant flowrate), than it is for the nonmodified surface in the range of surface temperatures from 120 to 140°C. The heat removal efficiency is better for the surface having a higher roughness. The removed heat flux convective component and phase change component in the case of surface cooling with dispersed flow are calculated. A conclusion has been drawn that the phase change makes a key contribution in this process. The quantity of dispersed coolant required to implement the above-mentioned cooling modes is estimated, and the dependence of its flowrate on the heat flux is obtained.