## Dew pointThe dew point is related to the vapor pressure of the liquids. It is defined as the temperature point at which the saturation vapor pressure (maximum pressure by the vapors at a given temperature) equals the present vapor pressure. The temperature below the dew point temperature causes the vapors to reach the condensation state. It means that below the dew point, the vapor condenses, and the rate of condensation becomes greater than that of the evaporation. The condensation water, when it freezes, is known as Let's consider an example of We know that water vapor is the gaseous form of water that contains water droplets. At the dew point, the air cannot hold more water in its gaseous state. We can also say that air is heavy and has no space for water droplets to fit into it. The higher the dew point, the more moisture the air would contain, which means the air's humidity increases. ## Dew point range in the atmosphereThe atmosphere at different dew points is listed in the below table:
## Humidity percentage at different temperaturesThe device used to measure the dew point temperature is a The table shows the humidity percentage at a different temperature range in Celsius as well as Fahrenheit.
The above data clearly depicts that the higher the temperature, the higher will be the humidity percentage in the air. ## Dew point formulaHere, we will discuss the dew point formula in terms of both degrees Celsius and degrees Fahrenheit. ## Dew point formula in degrees CelsiusThe dew point formula when the actual air temperature and the relative humidity are given is: Td = T - ((100 - RH)/5) Or RH = 100 - 5 (T - Td) Where, T d is the dew point temperature T is the actual air temperature RH is the relative humidity ## Dew point formula in degrees FahrenheitTd = T - (9(100 - RH)/25) Or RH = 100 - 25/9 (T - Td) Where, T d is the dew point temperature T is the actual air temperature RH is the relative humidity ## Dew point vs. humidityNow, we must be confused about the relation between the dew point and the relative humidity of the air. Both the terms are explained as follows: The dew point describes the For example, The temperature of the atmosphere is 28 degrees Celsius. The dew point temperature is also 28 degrees Celsius. It means that the saturation vapor pressure is also the same and the air is 100% humid. It cannot hold any more water vapors or moisture. Thus, the dew point can never be greater than the temperature of the air because humidity can never cross 100%. Now, The temperature of the atmosphere is 28 degrees Celsius. The dew point temperature is also 21 degrees Celsius. Using the above discussed formula, the relative humidity will now be 70%. ## Relationship of the dew point with the human comfortWhen the air temperature rises, the human body gets heated. The body uses the sweating method to cool down automatically. Hence, a person sweats more in the summers. The process of evaporation of sweat occurs faster because the air around us carries heat faster. On a normal day, one can also sweat by generating more body heat during exercise. The rate of sweating depends on the moisture in the air. If the air contains a high amount of moisture, the sweat will not evaporate. Thus, a person feels stickier and hot on humid days. When the perspiration (sweating process) starts, the air around a person starts taking heat from the body, and the warm air rises and gets replaced by the other air. If the air around a heated body is moved faster, the evaporation of the sweat occurs faster. Thus, the fan or any breeze increases the speed of the air around a person, and the evaporation occurs faster by cooling the body. The dried air with less moisture causes dryness resulting in discomfort. The recommended air inside the room or indoors is around the room temperature (25 degrees Celsius). ## Numerical ExamplesLet's discuss some numerical examples related to dew point.
Td = T - ((100 - RH)/5) Where, T d is the dew point temperature T is the actual air temperature RH is the relative humidity Putting the values in the above formula, we get: 25 = 30 - (100-RH)/5 125 = 150- (100-RH) 100 - RH = 150 - 125 100- RH = 25 RH = 100 - 25 = 75% Thus, the relative humidity is 75%.
Solution: the formula to calculate the dew point temperature is given by: Td = T - ((100 - RH)/5) Putting the values in the above formula, we get: Td = 35 - (100-80)/5 Td = 35 - (20)/2 Td = 35 - 10 Td = 25 Hence, the dew point temperature is 25 degrees Celsius.
RH = 100 - 25/9 (T - Td) Putting the values in the above formula, we get: RH = 100 - 25/9 (64 - 55) RH = 100 - 25/9 (9) RH = 100 - 25 RH = 75% Hence, the humidity is 75%. Next TopicUnit of electric charge |