On a cold winter morning or evening, you must have felt tiny droplets of water in the atmosphere or for that matter seen water droplets in the air in the form of fog on cold beverage containers during the hot season. But have you ever wondered what lies behind this natural phenomenon? The answer is dew point, which we will discuss in detail in this article.
Dew point, or otherwise better known as dew point temperature, is the temperature at which the liquid and gaseous phases of a material present in a gas, such as water in air, are in equilibrium at a given gas pressure. In the case of water, the temperature at which both evaporation and condensation of water take place are the same. An interesting point to note about dew point is that it is related with evaporation, condensation and relative humidity.
How Does Temperature Affect Dew Point?
It is a known fact that warmer air can hold or suspend more water vapor in the air than cold air. When the air cools down, it naturally loses its ability to hold moisture in the air. Dew point temperature is also known as the saturation temperature of water vapor in the air, the reason being that when the temperature is lowered from the saturation temperature, water vapor condenses faster than it evaporates. On the other hand, when the temperature is increased from the saturation temperature, water vapor evaporates faster than it condenses. At the saturation temperature, the evaporation and condensation rates of water vapor in the atmosphere are at equilibrium.
Dew Point vs. Humidity
As mentioned in our previous article, relative humidity is the amount of moisture or water vapor that is suspended in the atmosphere. Dew point and humidity have been found to be related and are dependent on the amount of water vapor in the air and the total amount of water vapor that the air can hold at a given temperature. This is the main reason why you see tiny droplets of water on cold surfaces during hot weather conditions.
When relative humidity increases, the dew point temperature is closer to the current air temperature and when relative humidity decreases, the dew point temperature is at par with the current air temperature. When dew point temperature and real temperature are the same, relative humidity is 100%. At this point of time, fog, mist, dew and clouds start forming due to condensation and this means that the air is holding 100% moisture.
Basic Points to Know about Dew Point
• Dew point temperature can never be higher than the current temperature.
• When the temperature is the same as the dew point temperature and then starts falling, the dew point temperature must simultaneous decrease.
• The amount of moisture in the air increases with increase in the dew point temperature.
• Relative humidity of around 100% is an indication of dew, frost, fog and rain.
• Regions around the Equator experience high dew points, whereas the desert and polar regions experience low dew points.
Applications
• Heat transfer by convection
• Combustion of fossil fuels and combustion engineering
• Drying of paper, cardboard, plastics, wood, tobacco, leather, printed goods, textiles and grain
• Energy efficiency in chemical manufacturing processes
• Prevention of corrosion in iron, steel and other metals
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References
1. http://www.temperatures.com/dewpoint.html
2. http://www.weatherquestions.com/What_is_dewpoint_temperature.htm
3. http://apollo.lsc.vsc.edu/classes/idm3020/tut_folder/nick_tutorial/
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