Effect of ambient pressure on Leidenfrost temperature

The accurate prediction and control of the interaction of liquids with hot surfaces is paramount in numerous areas, including cooling applications. We present results illustrating the effect of ambient pressure on the temperature required for a droplet to levitate over a hot surface, i.e., the Leidenfrost temperature. In the present study the dependence of wetting and levitating temperatures on ambient pressure in a range of subatmospheric pressures is reported. Experimental data indicate that the Leidenfrost temperature decreases with decreasing pressure at subatmospheric pressures. A physical approach for the dependence of Leidenfrost temperature on ambient pressure, based on an analogy with saturation pressure dependence, is proposed. Furthermore, previous literature data for pressures above atmospheric are also included in the analysis to support and validate the proposed approach. In addition, the effect of substrate material, substrate roughness, and type of fluid on the Leidenfrost temperature is discussed.

Figure 1

(a) Sketch of the experimental apparatus used in this study and (b) sketch of the heating substrate placed inside the chamber.

Figure 2

(Top) DSA100 snapshots of a droplet deposited on a heated substrate ($T$ = 105 °C), at different pressures: atmospheric, 600, 450, 300, 150, and 40 mm Hg. (Bottom) Sketch and high speed camera snapshots for the distinctive behaviors: (a) wetting regime, (b) transition regime, and (c) levitating regime.

Figure 3

Experimental results and fitted trends for (squares) Leidenfrost temperature, $T_L$ (deg C), and (circles) wetting temperature, $T_W$ (deg C), versus pressure (mm Hg). Liquid-vapor saturation curve from National Institute of Standards and Technology (NIST); solid line is included for comparison.

Figure 4

Experimental results of $T_L$ rearranged as ${1/T}_L$ (${\mathrm{K}}^{-1}$) versus ${log}_{10}\left[\mathrm{P}\right(\mathrm{mm}\mathrm{Hg}\left)\right]$ for water on (open squares) aluminum, (open hexagons) Monel [8], (open triangles) brass [8], (open diamonds) stainless steel (rms = 0.34 $\mu \mathrm{m}$) [8], and (open pentagons) aluminum [14]. (Top-full squares) iso-octane on aluminum [16] and (top-full circles) $n$-heptane, (top-full diamonds) α-methylnaphthalene and (top-full pentagons) $n$-hexadecane on stainless steel (rms = 0.2 $\mu \mathrm{m}$) [15]. (Top-full triangles) estimated $T_L$ under pressure for $n$-heptane on stainless steel (rms = 0.2 $\mu \mathrm{m}$) [15]. (Open circles) $T_W$ for water on aluminum is also presented. Linear trends as $1/T$ versus ${log}_{10}\left[P\right]$ and linear trend without symbols for $1/T_{\mathrm{sat}}$ versus ${log}_{10}\left[P_{\mathrm{sat}}\right]$ are included to support the discussion. Note that different sets of experimental data exhibit different slopes since these latter depend on the nature and state of the heating substrate as well as the fluid.

Figure 5

Slope $B$ for water versus thermal diffusivity of (square) aluminum, (diamond) stainless steel, and (triangle) brass.