Dew point is called the maximum temperature at which achievement in the conditions of the set humidity there is a saturation of water vapor in air. As the dew point depends on humidity, its definition is the cornerstone of the principle of work of a psikhrometrichesky hygrometer.
Instruction
1. Remember that an indispensable condition of definition of a dew point in all listed ways is the positive value of the air temperature expressed in degrees Celsius.
2. If you have a psikhrometrichesky table, and in statements of the problem temperature air and its humidity are specified, in the beginning transfer temperature to degrees Celsius. Then find the corresponding parameters, respectively, in the top horizontal line and the left vertical column of this table. On their crossing there will be dew point temperature expressed also in degrees Celsius. If necessary transfer result to kelvins.
3. Also it is possible to find a dew point in the mathematical way. For this purpose at first transfer the air temperature specified in statements of the problem to degrees Celsius. Then find auxiliary parameter γ on the following formula: γ= (17.27T / (237.7+T)) the relative air humidity, % is +ln(RH) where T is the air temperature of °C, RH.
4. Now substitute auxiliary parameter γ in the second formula looking as follows: Tp=237.7γ/17.27-γ) where Tp is dew point temperature, γ - the size determined during the previous calculation.
5. In the presence of a psikhrometrichsky hygrometer (but not a hygrometer of other type) it is possible to define a dew point and directly. For this purpose in the beginning make sure that preparation of the device for work was made long ago, and it came to an operating mode. Then read indications of the damp thermometer - they will be equal to a dew point. If it is required to find only this size, but not humidity of air, even use of the psikhrometrichesky table located on the case of the device will not be required.
6. Transfer result of calculation or direct determination of temperature of a dew point to those units in which it has to be expressed according to statements of the problem. It can be kelvins and also degrees Celsius, Fahrenheit, etc.