Advances and challenges in explaining fuel spray impingement: How much of single droplet impact research is useful?

Recent demands for superior material properties and more efficient use of materials and production time are forcing manufacturers to develop intelligent processing techniques for enhanced process control in order to better dictate the end product. In the heat treatment and processing of metallic alloys, the desire to obtain parts of enhanced and uniform mechanical properties is requiring increased control over heat removal rates and enhanced temperature control. In particular, spray quenching has been shown to be an effective means to control and enhance the cooling rates of heat treatable aluminum alloys. This study presents a detailed and thorough parametric study of the Leidenfrost point (LFP), which serves as the temperature boundary between the transition and film boiling regimes. Sessile drop evaporation experiments were conducted with acetone, benzene, FC-72, and water on heated aluminum surfaces with either polished, particle blasted, or rough sanded finishes to observe the influential effects of fluid properties, surface roughness, and surface contamination on the LFP. A weak relationship between surface energies and the LFP was observed by performing droplet evaporation experiments with water on polished copper, nickel, and silver surfaces. Additional parameters which were investigated and found to have negligible influence on the LFP included liquidmore » subcooling, liquid degassing, surface roughness on the polished level, and the presence of polishing paste residues. The accumulated LFP data of this study were used to assess several existing models which attempt to identify the mechanisms which govern the LFP. The disagreement between the experimental LFP values and those predicted by the various models suggests that an accurate and robust theoretical model which effectively captures the LFP mechanisms is currently unavailable.« less

The Leidenfrost point : Experimental study and assessment of existing models

Effects of surface roughness on water droplet impact history and heat transfer regimes

In the present work, the effects of surface chemistry and micro/nanostructuring on the Leidenfrost temperature are experimentally investigated. The functional surfaces were fabricated on a 304 stainless steel surface via femtosecond laser surface processing (FLSP). The droplet lifetime experimental method was employed to determine the Leidenfrost temperature for both machine-polished and textured surfaces. A precision dropper was used to control the droplet size to 4.2 μL and surface temperatures were measured by means of an embedded thermocouple. Extraordinary shifts in the Leidenfrost temperatures, as high as 175 °C relative to the polished surface, were observed with the laser-processed surfaces. These extraordinary shifts were attributed to nanoporosity, reduction in contact angle, intermittent liquid/solid contacts, and capillary wicking actions resulting from the presence of self-assembled nanoparticles formed on the surfaces. In addition to the shift in the Leidenfrost temperature, significant enha...

http://ncesr.unl.edu/wordpress/wp-content/uploads/2013/08/Extraordinary-Shifts-of-the-Leidenfrost-Temperature-from-Multiscale-MicroNanostructured-Surfaces.pdf

Extraordinary shifts of the Leidenfrost temperature from multiscale micro/nanostructured surfaces.

http://www.aerolab.mech.ntua.gr/2phase_isothermal/A%20numerical%20investigation%20of%20the%20evaporation%20process%20of%20a%20liquid%20droplet%20impinging%20onto%20a%20hot%20substrate.pdf

A numerical investigation of the evaporation process of a liquid droplet impinging onto a hot substrate

Surface roughness and contamination, drop volume and liquid subcooling effects on Leidenfrost temperature

/pdf/role-of-the-surface-in-the-measurement-of-the-leidenfrost-3djw40aad2.pdf

F. F. Simon

Papers

Role of the surface in the measurement of the Leidenfrost temperature