Leidenfrost Point
The Leidenfrost point signifies the onset of stable film boiling. It represents the point on the boiling curve where the heat flux is at the minimum and the surface is completely covered by a vapor blanket. Heat transfer from the surface to the liquid occurs by conduction and radiation through the vapor. In 1756, Leidenfrost observed that water droplets supported by the vapor film slowly evaporate as they move about on the hot surface. As the surface temperature is increased, radiation through the vapor film becomes more significant and the heat flux increases with increasing excess temperature.
The minimum heat flux for a large horizontal plate can be derived from Zuber's equation,
where the properties are evaluated at saturation temperature. Zuber's constant, C is approximately 0.09 for most fluids at moderate pressures.
Read more about this topic: Leidenfrost Effect
Famous quotes containing the word point:
“It used to be said that, socially speaking, Philadelphia asked who a person is, New York how much is he worth, and Boston what does he know. Nationally it has now become generally recognized that Boston Society has long cared even more than Philadelphia about the first point and has refined the asking of who a person is to the point of demanding to know who he was. Philadelphia asks about a man’s parents; Boston wants to know about his grandparents.”
—Cleveland Amory (b. 1917)