Mechanism and experiment of dewetting of drag reduction nanoparticles adsorbed on core surface

Key words:  hydrophobic nanopartices  adsorption layer  dewetting  critical coverage ratio  drag reduction

Abstract:

The adsorbed hydrophobic nanoparticles on the core wall can form super hydrophobic layer due to the dewetting, which is the key to Nanofluid drag reduction technology. The critical coverage rate of hydrophobic spherical nanoparticles after adsorption on hydrophilic surfaces was investigated by thermodynamic theory. The main factors affecting the dewetting and their influences were discussed by using the actual reservoir parameters, and the mechanical mechanism of the dewetting was analyzed as well. The dewetting experiment of the core surface adsorbed by nanoparticles was carried out, and the wettability of the core surface and the coverage rate of nanoparticles were studied. The results show that the dewetting requires the coverage rate of nanoparticles is larger than the critical coverage rate. And increasing the particle contact angle and the contact angle of the substrate, or reducing the particle size or reducing the fluid-gas pressure difference can reduce the critical coverage rate, which is beneficial to the dewetting. After the hydrophobic nanoparticles adsorb on the core surface, the surface contact angle increases from 30° to 127°, the particle coverage rate reaches 74%, which is greater than the critical coverage rate of 72%. The results indicate that the dewetting could be induced by the adsorption of hydrophobic nanoparticles, which verifies the accuracy of the theoretical analysis.