Chapter 18, Problem 62P

Leidenfrost effect. A water drop will last about 1 s on a hot skillet with a temperature between 100°C and about 200°C. However, if the skillet is much hotter, the drop can last several minutes, an effect named after an early investigator. The longer lifetime is due to the support of a thin layer of air and water vapor that separates the drop from the metal (by distance L in Fig. 18-48). Let L = 0.100 mm, and assume that the drop is flat with height h = 1.50 mm and bottom face area A = 4.00 × 10^–6 m². Also assume that the skillet has a constant temperature T_s = 300°C and the drop has a temperature of 100°C. Water has density ρ = 1000 kg/m³, and the supporting layer has thermal conductivity k = 0.026 W/mžK. (a) At what rate is energy conducted from the skillet to the drop though the drop's bottom surface? (b) If conduction is the primary way energy moves from the skillet to the drop, how long will the drop last?

Figure 18-48 Problem 62.