Mixed-surfactant additives for enhancement of air-atomized spray cooling of a hot steel plate

The current study covers the cooling enhancement of a hot stainless steel plate using mixtures of ionic and nonionic surfactant additives in air-atomized water spray. The surfactant when dissolved in water, exhibits surface activity to influence the atomization process as well as solid-liquid contact by forming a monolayer at air-water interface. The properties of monolayer formed by mixed-surfactant systems depend on the interactions between the surfactants such that the heat transfer rate differs from that of the surface. In this study, sodium dodecyl sulfate (an anionic surfactant), cetrimonium bromide (a cationic surfactant), and polysorbate 20 (Tween 20, a nonionic surfactant) have been used. For detailed analysis on heat transfer performance of mixed-surfactants, the optimum concentration levels of the three surfactants have been considered from the authors' earlier work. A test plate of AISI 304 designated steel of surface area 100 mm × 100 mm and a thickness of 6 mm has been employed with three subsurface thermocouples to collect the transient temperature data during cooling from an initial surface temperature of 900 °C. A commercial inverse heat conduction software, INTEMP has been used to estimate the surface heat flux and temperatures such that the cooling rates can be calculated for all the experiments. The results are analyzed to see the effect of mixed-surfactants on cooling performance of the hot plate, which reveal that the mixtures of nonionic and ionic surfactants give higher heat transfer enhancement than those of the individual surfactants in water. However, catanionic surfactant mixture diminishes the heat transfer ability of pure water. Overall, a maximum cooling rate of 240 °C/s and heat transfer co-efficient of 20,000 W/m2 °C can be achieved from this study which is very important for run-out table cooling of a Hot Strip Mill in steel industry.