Dew Point
2008
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Dew Point
Reasons Of Dew And Fog Formation
Dew and fog are probably the most poetic things anyone can imagine. Fogs play different roles in movies, they create suspense or lead to a flash back but they are real and are made up of something. Dew lives up to its name, it is found on cool surfaces in the early morning like leaves, grass, trees, plants, window panes and car’s wind shields.
Dew is basically made of water but its water is condensed from water vapor in the air. Dew forms when vapor is reduced to liquid in the earth’s atmosphere. This usually starts at night and continues till early morning. It is strange enough to observe that dew forms faster on car windows than on grass. The point at which vapor gives way to a dew is called dew point.
Fog is formed when air above the ground cools down. Dew forms only on the surface that cools down while a thin layer of air drops water vapors to grass, trees, leaves and other surfaces while a fog is formed in the same way as a cloud and it basically comes from a cloud that has come close to the surface of the earth.
Another way of looking at dew formation is to observe a cold can of soda. When the can has cold soda inside and a warm temperature outside and as the two meet, the air caught up in the middle cools down resulting in water molecules in the air to bind with one another. When they condense, they form water droplets on any surface nearby.
Even in the world’s driest places like the sub Saharan region has an observable dew formation every time. In places where there is virtually no rain fall throughout the year, dew has its place. Although It looks weird but dew can be denser than rainfall in these areas. Dew forms in extremely hot places when the soil’s surface temperature drops below the supposed dew point.
When looking closer in to the formation of fog, it is formed when humidity rises to almost a 100%. Besides that, its formation requires that the difference between dew point and air temperature which should be 5 degrees F or a little lower. Water droplets jell together in this condition and become too heavy to rise any higher.
There are around twelve kinds of fogs but the most common are radiation fog, ground fog, steam fog, evaporation fog and valley fog.
Dew and fog both have such a soothing effect on one’s mind. The cooling effect of dew is so much inspirational that popular drinks have been named after it.
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Also learn in details why does dew form and why does fog form
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What is the mole fraction of water in the air and the dew point?
The weather man on channel 5 says the following: The temperature is 78 degrees F, the barometric pressure is 29.9 inches, and the relative humidity is 87%." What is the mole fraction of water in the air and the dew point?
Get a Psychrometric Chart.
Following the abscissa (horizontal coord.) go to 87 deg. F (this is Dry Bulb) go then up along the ordinate (vertical coord.) until intersects 87% Relative Humidity, from that point, go right again along the abscissa until intersect water content, if units are given in pounds of water per pound of air, get the percentage by weight and transform to the proper values of molecular weights, the answer must come as % of moles of water to moles of air.
If the Psychrometric chart gives you the values in grains per pound of air. divide grains by 700 to get pounds.
Humidity vs Dewpoint
