Leidenfrost point

The temperature drop corresponding to point C is called the critical temperature drop, and the flux at point C is the peak flux. In the third segment, line CD in Fig. 13.4, the flux decreases as the temperature drop rises and reaches a minimum at point D. Point D is called the Leidenfrost point. In the last segment, line DE, the flux again increases with AT and, at large temperature drops, surpasses the previous maximum reached at point C. 

Because, by definition, h = q[A)IAT, the plot of Fig. 13.4 is readily convertible into a plot of h vs. AT This curve is shown in Fig. 13.5. A maximum and a minimum coefficient are evident in Fig. 13.5. They do not, however, occur at the same values of the temperature drop as the maximum and minimum fluxes indicated in Fig. 13.4. The coefficient is normally a maximum at a temperature drop slightly lower than that at the peak flux the minimum coefficient occurs at a much higher temperature drop than that at the Leidenfrost point. The coefficient is proportional to AT in the first segment of the line in Fig. 13.4 and to between AT and AT in the second segment. 

Near the Leidenfrost point another distinct change in mechanism occurs. The hot surface becomes covered with a quiescent film of vapor, through which... 

Keywords Contact angle Corona splashes Disintegration Disintegration limits Droplet impact Drop surface energy Heat transfer regimes Leidenfrost point Molten metal droplet impact Rupture Secondary atomization Spread Surface topography Thermal induced atomization Wettability... 

J. D. Bemardin, I. Mudawar The Leidenfrost point Experimental study and assessment of existing models, Trans. ASME, 121, 894—903 (1999). 

H. Xie, Z. Zhou A model for droplet evaporatitm near Leidenfrost point, Int. J. Heat Mass Transfer, 50, 5238-5333 (2007). 

Liquid Marbles, Fig. 2 The evaporation time of liquid marbles and water droplets at different surface temperatures. Liquid marbles feature long evaporation time at all tested temperatures. Water droplets feature the same long evaporation time only when the temperature is beyond the Leidenfrost point. If the temperature is below the Leidenfrost point, water droplets usually evaporate within seconds. A theoretical curve for Leidenfrost phenomenon is also plotted for comparison (Reproduced with permission from Aberle et al. [5])... 

The heated evaporation of graphite liquid marbles on a superheated substrate was investigated at various surface temperatures and compared with pure water droplets. It is found that if the temperature is above the Leidenfrost point, the evaporation time of liquid marbles and water droplets are almost the same, whereas if the temperature is below the Leidenfrost point, water droplets evaporate much faster and liquid marbles still exhibit the Leidenfrost-like effect. It is postulated that the prolonged evaporation time of... 

This is because at temperatures above the Leidenfrost point, and the bottom part of the water droplet vaporizes immediately in contact with the hot plate. The resulting gas suspends the rest of the water droplet just above it, preventing any further direct contact between the liquid water and the hot plate. As steam has much poorer thermal conductivity, and further heat transfer between the pan and the droplet is slowed down dramatically. This also results in the drop being able to skid around the pan on the layer of gas just under it. 

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