Evaporation

Examples of Evaporation in the following topics:

• Evaporation

  • This phenomenon is also called evaporative cooling.
  • This is why evaporating sweat cools the human body.
  • Evaporation is an essential part of the water cycle.
  • In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration.
  • (b) If the container is sealed, evaporation will continue until there is enough vapor density for the condensation rate to equal the evaporation rate.

• Humidity, Evaporation, and Boiling

  • The amount of water vapor in air is a result of evaporation or boiling, until an equilibrium is reached.
  • If a lid is placed over the container, as in (b), evaporation continues, increasing the pressure, until sufficient vapor has built up for condensation to balance evaporation.
  • This phenomenon is also called evaporative cooling.
  • This is why evaporating sweat cools the human body.
  • Thus, it can evaporate without limit at this temperature and pressure.

• The Evaporating Atmosphere

  • At equilibrium, evaporation and condensation processes exactly balance and there is no net change in the volume of either phase.
  • At equilibrium, evaporation and condensation processes exactly balance and there is no net change in the volume of either phase.

• Heat Pumps and Refrigerators

  • The basic components of a heat pump in are a condenser, an expansion valve, an evaporator and a compressor .
  • In the outdoor coils (the evaporator), heat transfer Qc occurs to the working fluid from the cold outdoor air, turning it into a gas.
  • The liquid then flows back through a pressure-reducing valve to the outdoor evaporator coils, being cooled through expansion.
  • (In a cooling cycle, the evaporator and condenser coils exchange roles and the flow direction of the fluid is reversed. )
  • A simple heat pump has four basic components: (1) condenser, (2) expansion valve, (3) evaporator, and (4) compressor.

• Convection

  • Heat from the skin is required in order for sweat to evaporate from the skin, but without air flow the air becomes saturated and evaporation stops.
  • Air flow caused by convection replaces the saturated air by dry air and thus evaporation continues.
  • Another important example of the combination of phase change and convection occurs when water evaporates from the ocean.
  • Heat is removed from the ocean when water evaporates.

• Latent Heat

  • The system is constructed so that no vapor evaporates while ice warms to become liquid water, and so that, when vaporization occurs, the vapor remains in of the system.

• Phase Changes and Energy Conservation

  • Only after it has completely evaporated will it get any hotter.