LATENT HEAT OF VAPORIZATION

When a pure substance is liquefied from the solid-state or vaporized from the liquid at constant pressure, no change in temperature occurs; however, the process requires the transfer of a finite amount of heat to the substance. These heat effects are called the latent heat of fusion and the latent heat of vaporization.

  v The amount of heat gained by a solid object to convert it into a liquid without any further increase in the temperature is known as the latent heat of fusion.

  v The heat required to change one mole of liquid at its boiling point under standard atmospheric pressure is called the latent heat of vaporization.

DAILY LIFE EXAMPLE:

v LPG TANK

v PSYCHROMETERS

LPG TANK

When the LPG is consumed in a cylinder with a fast flow, dew formation takes place at the upper parts of the cylinder and the valve exit. This formation is observed due to the heat transfer from cylinder exit to the environment in which case the heat required is supplied from the evaporation of LPG.

PSYCHROMETERS

Psychrometer is a laboratory device that is used to calculate relative humidity of the ambient air by measuring the dry-bulb and wet-bulb temperatures. The temperature difference between dry-bulb and wet-bulb thermometers is due to the evaporation of water on the wet-bulb until it reaches equilibrium with the ambient humidity. By psychrometric charts, it is possible to calculate the air humidity according to these temperature values.