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• Spray cooling heat transfer of various surface structures are investigated numerically. • 3D Euler-Lagrangian simulation is performed and wall-film model is used. • Liquid film thickness and streamlines are computed in the vicinity of different fin geometries. • Local film thickness increases in grooves. • The film velocity magnitude depends on the fin blockage. Liquid impingement cooling in the form of jet or spray is an appropriate method to remove heat from small surfaces progressively utilized in industry. In this study, numerical simulations are conducted to investigate the effect of surface structure on heat transfer characteristics. Five different three-dimensional structured surfaces are investigated using Euler-Lagrangian approach. The effect of surface structures is discussed on the liquid film thickness, the liquid film velocity, and the heat flux with its uniformity for a given spray and temperature characteristics. The results show that the convective heat transfer strongly depends on both liquid film thickness and velocity. While the liquid film thickness always grows in the grooved surfaces, its velocity depends on the form and direction of the fins. The averaged values of the film thickness and velocity magnitude are almost independent of the surface temperature. Among the investigated surfaces, the parallel and circular patterns showed the best and worst performance on heat transfer characteristics, respectively. [ABSTRACT FROM AUTHOR]

A study of heat transfer and film dynamics caused by single and multiple streams of impinging droplets using HFE-7100 as the cooling liquid under constant heat flux conditions is presented. Single and multiple streams of mono-dispersed droplets were produced using a piezoelectric droplet generator with the ability to adjust parameters such as droplet impingement frequency, droplet diameter, droplet velocity, and spacing between adjacent impinging droplet streams. In this study, a heater consisting of a thin layer of Indium Tin Oxide (ITO) as heating element, combined with a Zinc Selenide (ZnSe) substrate was used for characterizing the heat transfer behavior and hydrodynamic phenomena of impinged liquid films near or at the onset of critical heat flux (CHF). Film thickness inside the impact crater was measured using the Total Internal Reflection (TIR) technique. Hydrodynamic phenomena of the droplet impact craters were analyzed using a high speed imaging technique. Impact regimes of the impinging droplets were identified and classified, and their effects on heat transfer performance are discussed. The study supports the notion that forced convection is the main heat transfer mechanism inside the impact crater due mainly to the high frequency and periodic nature of droplet impingement. Furthermore, droplet impingement regimes such as spreading and splashing have been observed to play an important role in the overall heat transfer behavior. Spacing between adjacent impinging droplet streams is also an important factor in surface cooling when multiple droplet streams are used. [ABSTRACT FROM AUTHOR]