Evaporation of water droplets with metallic inclusions

The dynamics of non-axisymmetric evaporating droplet with metallic inclusions heated in a high-temperature gas flow are experimentally studied. The type of metallic inclusion is found to play a critical role in the transient flow dynamics and associated heat transfer. Experiments were conducted with eight metals and alloys currently used in industrial applications. High-speed recording (up to 102–104 frames per second) allowed measuring lifetimes of water droplets with different metallic inclusions (1 mm or 2 mm in size) when increasing the gas temperature from ∼300 K up to about 900 K. We propose a candidate mechanism of evaporation that explains the differences between measured droplet lifetimes in the performed tests. Furthermore, the conditions to provide the most effective cooling are determined. They are based on the balance equations taking into account warm-up times of inclusions and the ratio between the latent heat of vaporization of water, the energy used to heat up water and the metallic particles.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Water drops with graphite particles triggering the explosive liquid breakup

We have established conditions for stable triggering of the explosive breakup for heterogeneous water drops induced by immersion in high-temperature gas (air) at more than 800 K. The water drop heating is enhanced by small graphite solid particles of 2 × 2 × 1 mm, 2 × 2 × 2 mm and 2 × 2 × 3 mm inserted into drops. The properties of the graphite such as porous and layered structure, moisture content, and surface roughness play determining roles. Experiments show that heterogeneous water drops can boil during a short time and produce clouds of tiny droplets. Heating times of heterogeneous drops until the breakup do not exceed a few seconds and usually last for less than three. We have identified the main stages and the mechanism of heterogeneous drop heating, as well as vaporization at the internal interface and at the free surface of a drop. A high-speed video camera and the TEMA Automotive Software with a number of tracking algorithms are used for measurements. The analysis of experimental results shows that during the fragmentation of large heterogeneous drops at high temperatures, more than 100 small droplets are formed. The obtained data are a basis for novel technologies of effective fire extinguishing that involve the multiple growth of water evaporation area in a flame.SCOPUS: ar.jinfo:eu-repo/semantics/publishe