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:
“The point is, that the function of the novel seems to be changing; it has become an outpost of journalism; we read novels for information about areas of life we don’t know—Nigeria, South Africa, the American army, a coal-mining village, coteries in Chelsea, etc. We read to find out what is going on. One novel in five hundred or a thousand has the quality a novel should have to make it a novel—the quality of philosophy.”
—Doris Lessing (b. 1919)