Pool boiling - Modes of Pool Boiling Boiling – when...

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Unformatted text preview: Modes of Pool Boiling Boiling – when evaporation occurs at a solid-liquid interface Occurs when the temperature of the surface T s exceeds the saturation temperature T sat corresponding to the liquid pressure. Relative humidity = P v / P g When relative humidity is less than 100%. Evaporation occurs at liquid-vapor interface. This is the situation most of the time in the atmosphere. This is not boiling. P v is the partial pressure of the vapor, P g is the saturation pressure. If T s is less that T sat , the pressure in the liquid (which is the same at the atmosphere above it plus ρgh), then the pressure is high enough to keep the fluid in a liquid form. When T s is greater than T sat , the pressure in the liquid is no longer high enough to keep the fluid in a liquid form. The fluid “boils” and turns from a liquid into a vapor creating bubbles that then rise to the surface carrying heat with them. Atmospheric pressure At 5000 ft, p = .843 bars, boiling occurs approx. 368 (about 5 K or 9 °F lower) Saturated boiling – temperature of the liquid slightly exceeds the saturation temperature Saturation temperature – temperature at which vaporization takes place at given pressure Sub-cooled boiling – temperature of the liquid is below the saturation temperature -ex: drop a hot marble into cold water Temperature Distribution in saturated pool boiling with a liquid-vapor interface...
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Pool boiling - Modes of Pool Boiling Boiling – when...

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