Thermodynamic spreading behaviors of oil on rough surfaces of stainless steel 316L

Thermodynamic spreading behaviors of oil were especially important for normal operation of equipment in the state of lubricating oil starvation, which were investigated experimentally and theoretically in this manuscript. Three rough surfaces of stainless steel 316L were obtained by grinding with sandpaper 600 mesh, 1000 mesh, 1500 mesh respectively. Spreading behaviors of lubricating oil 60N were studied on these rough surfaces with uniform temperature and temperature gradient separately, which were achieved by self-assembled apparatus, and a comparison for oil spreading performance was conducted between the two temperature conditions. In order to analyze the problem theoretically, a model for rough surfaces was built by assuming the profile of any rough peak and valley to be a parabola and distributed uniformly. It was found that the higher the surface temperature and the rougher the surface, the larger the oil spreading distance and velocity for surfaces with uniform temperature. For surfaces with a temperature gradient, directional motion of oil occurred when the temperature gradient was larger than 1.61 degrees C/mm. Although the oil droplet had the same starting temperature, however, the spreading velocity was larger on surfaces with smaller roughness, which was opposite with that with uniform surface temperature. In addition, the theoretical model could be used to describe the stable phase after oil droplet forming a relatively stable contact angle by comparing the computational results with experimental ones under temperature gradient conditions.