A wet-bulb thermometer consists of a mercury-in-glass thermometer covered with a wetted (water) fabric. When suspended in a stream of air, the steady-state thermometer reading indicates the wet-bulb temperature Twb. Obtain an expression for determining the relative humidity of the air from knowledge of the air temperature (T∞), the wet-bulb temperature, and appropriate air and water vapor properties. If T∞ = 45°C and Twb = 25°C, what is the relative humidity of the airstream?