The partial pressure of water vapor is very low, it is much lower than the saturated vapor pressure of pure water at the same temperature, so it has a strong hygroscopic property. The equilibrium between liquid and vapor is a dynamic equilibrium in which the rate at which the molecules pass through the surface of the liquid into the vapor is equal to the rate at which the molecules return from the vapor into the liquid. Because the charm of lithium bromide molecules in lithium bromide solution for water molecules than the attraction between water molecules is strong, also because of the existence of the lithium bromide molecules in a liquid volume in the unit and reduce the number of water molecules, so in the same conditions of temperature, the number of the unit steam volume liquid surface in the inland waters molecular number less than pure water surface water molecule.
Because of the high boiling point of the lithium bromide, adopt the temperature range of not volatilize, so total solution in equilibrium, and steam pressure is equal to the pressure of water vapor, which equals the known temperature, lithium bromide solution on the surface of the water vapor partial pressure less than the saturated vapor pressure of pure water, and the higher the concentration or temperature lower water vapor partial pressure of the low.
If the saturated evaporation pressure of water is greater than 0.85kPa, such as the pressure of 1kPa (equivalent to the saturation temperature of 7℃), the lithium bromide solution has the ability to absorb it, that is to say, the lithium bromide water solution has the ability to absorb water vapor at a temperature lower than it, which is one of the mechanisms of the lithium bromide absorption refrigerator. Similarly, if the pressure is the same, the saturation temperature of the solution must be higher than the saturation temperature of the water, and the water vapor produced in the solution is always overheated.
