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To investigate the spray cooling characteristics and the impact of spray parameters such as chamber pressure, spray height, and spray tilt angle on heat transfer efficiency, a mathematical model based on the Eulerian–Lagrangian frame was established for an R410A closed-loop spray cooling system. The results revealed that the spray pattern is conical, with the center velocity significantly higher than the edge velocity. The temperature distribution of the cooling surface and liquid film height both exhibit a "W" shape, and the surface temperature is lower where the liquid film is thin. There is an optimal liquid film height of approximately 5 μm, at which the cooling surface temperature is the lowest. The surface temperature increases with an increase in the spray chamber pressure. Considering average cooling surface temperature, the optimal tilt angle is 40° with an average surface temperature of 330.1 K. When considering wall temperature and wall heat transfer coefficient uniformity, however, the optimal tilt angle is 10°, leading to the average surface temperature of 332.6 K. When increasing the optimal spray height to 70 mm, the average surface temperature is 313.4 K. [ABSTRACT FROM AUTHOR]

A commonly-used method to cool rotating cylinders involves spraying water on the surface to cool its internal particles. This paper conducted a numerical investigation of heat transfer from a rotary cylinder cooled with sprayed water. A 3-D numerical model was generated, and the distributions of the wall temperatures and liquid films were analyzed. Then, the heat transfer characteristics for different parameters were obtained and compared. The results showed that the best location for a single spray nozzle was directly above the cylinder, where it had the most uniform liquid film and highest heat exchange efficiency. With increased rotation speeds, the cylinder wall temperature increased and the distribution of wall temperature and liquid film became more uniform, which improved heat transfer. Because of the influence of gravity, the slope of the cylinder had a negative influence on the distribution of the liquid film. When the cylinder material had lower thermal conductivity, the system needed a much longer period of time before it was stable and had lower heat flux. Furthermore, with the same heat source, the system heat flux could not be determined with only the outer surface temperature, but with the temperature difference between inner surface and outer surface. [ABSTRACT FROM AUTHOR]

• 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]

• For Weber < 6000 and T ≤ T s a t , droplet dynamics is only affected by the impact velocity. • Droplet spreading diameter was found to be independent of surface temperature. • Low impact velocities are better at heat removal than high velocities. • A physics-based model is developed to predict the transient surface temperature. Single droplet impingement on a heated surface is a fundamental problem of basic interest in understanding complex phenomena in spray cooling and other applications involving heat transfer to impinging droplets. The surface temperature experiences rapid temporal gradients upon droplet impact. These temperature transients are strongly dependent on the hydrodynamic and heat transfer regimes. Experimental results are presented for the transient surface temperature in the film evaporation heat transfer regime for water drop diameters of 2.1 and 3.5 mm at drop Reynolds numbers up to 34,000 and Weber number up to 5540 are reported for surface temperatures of 60 to 100 ∘ C. High-speed video was used to capture the dynamics of the impact. Intrinsic thermocouples were manufactured to measure surface temperature with sufficient temporal resolution. It was found that the hydrodynamics of the impact were not significantly affected by the surface temperature. Heat removal was found to be more effective at lower impact velocities. The maximum temperature drop occurred at the maximum spreading diameter. An analytical model was developed to successfully predict the transient Nusslet number of the droplet motion on the surface for both free-falling and air-propelled droplets. [ABSTRACT FROM AUTHOR]

• Liquid film morphologies are defined as 'continuous, interacted, and isolated' types. • The interval of wetted areas for the isolated films under P = 0.2 MPa is [0.11, 1.54] mm2. • The distributed and surface-averaged velocity of isolated films are predicted. Although the understanding of spray cooling has significantly improved, knowledge of the heat transfer mechanisms is still limited, and the related models based on experiments are separated from physical phenomena. As an example, while liquid film morphology have been investigated in detail, comparatively little is known about how the liquid films evolve on the surface, owing to the strong interaction and disturbance between atomised droplets and thin films with high turbulence. In this study, the liquid film dynamics of HFE-7000 spray in a two-phase cooling regime on a smooth and unpolished silicon surface were quantitatively captured, including the film morphology, film velocity, wetted area, and contact line length, under different inlet pressures and heat fluxes. Owing to the thermally induced agglomeration with increasing heat flux, the continuous liquid film finally dispersed into an isolated state, which is quantitatively defined as the 'isolated film regime' by the critical interval of the wetted area. The velocity of the isolated film under various conditions is a consequence of the radial velocity of the atomised droplets, surface conditions, and surface temperature gradient. Based on the correlation of the radial velocity of atomised droplets, prediction methods for the distribution and surface-averaged velocity of isolated films are proposed. [ABSTRACT FROM AUTHOR]