(Lisbon Symposia会议论文)去除由于液滴/壁面相互作用导致的二次雾化的表面形貌影响

The present paper addresses the scaling of the effects of surface topography in the size of the secondary droplets generated by thermal induced atomization of single droplets impinging onto heated solid surfaces. The size and velocity of the secondary droplets is characterized making use of simultaneous image analysis and phase Doppler measurements to evaluate extended size distributions from 5.5μm up to a few millimetres. This procedure assured a consistent comparison of the results reported here with those previously reported in the literature, in similar experimental conditions. Although the study covers the various heat transfer regimes, particular attention is put on the phenomena occurring within the nucleate boiling regime, up to the critical heat flux temperature of the working fluids, as this is the upper boundary for the safe working conditions of many practical systems of interest, in the context of droplet/spray cooling. The analysis focus on the physical description of the phenomena occurring at the liquid-solid interface to explain the triggering of the secondary atomization and leads to an empirical relation between the mean size of the secondary droplets and the dimensionless topographical parameter Ra/λR, which quantifies the relative magnitude of the high of the rough grooves with the distance between them. This relation seems to describe well the results that were uncorrelated in previous work, thus explaining the large discrepancies coming from experiments performed under apparently similar conditions, which are mainly introduced by surface topography.