Читать книгу The ESD Control Program Handbook - Jeremy M. Smallwood - Страница 43

The relative humidity (rh) or dew point of the atmosphere has a large influence on electrostatic phenomena (see Section 1.2.6). At any temperature, moisture‐saturated air in equilibrium contains a maximum amount of moisture determined by the saturated vapor pressure of water at that temperature (Lawrence 2005). The saturated vapor pressure of water and hence the amount of moisture in saturated air increase strongly with increasing temperature. This saturated state is defined as 100% r.h. The relative humidity of air with lower than the saturated amount of water vapor present is given by

As the saturated vapor pressure increases strongly with temperature, if the amount of moisture present remains the same, increasing the air temperature will result in a reduction in relative humidity. Conversely, lowering the temperature will increase the humidity.

If the temperature is lowered sufficiently, the water vapor pressure eventually becomes equal to the saturated vapor pressure, and the air becomes saturated. Any further reduction in temperature may result in moisture condensing from the air on to surfaces in contact with it or in fog forming. This temperature is called the dew point.