Psychrometrics

Step 1: Define Relative Humidity (RH). Relative humidity is a measure of the amount of moisture in the air compared to the maximum amount of moisture the air can hold at that temperature.

Step 2: Express the definition mathematically. For ideal gases, the partial pressure of a component is proportional to its mole fraction ( ). Therefore, the ratio of partial pressures is equal to the ratio of mole fractions.
Since and : This exactly matches the definition given in the question. The other terms are different concepts: Specific Volume is volume per unit mass, and Wet Bulb and Dew-Point are temperatures.

Step 1: Describe a psychrometric chart. It is a graph that plots the thermodynamic properties of moist air. The horizontal axis is the dry-bulb temperature, and the vertical axis is the humidity ratio (or specific humidity).

Step 2: Identify the main curves on the chart. The chart contains various lines representing properties like wet-bulb temperature, specific volume, and relative humidity.

Step 3: Locate the saturation line. The prominent curved line that forms the upper-left boundary of the chart is the saturation curve. Along this entire line, the air is saturated with water vapor. By definition, saturated air has a relative humidity of 100%. Therefore, this curve represents 100% relative humidity.

Step 1: Define Relative Humidity (RH). Relative humidity is the ratio of the actual amount of water vapor present in the air to the maximum amount of water vapor the air could hold at that specific temperature.

Step 2: Define "saturated air". Saturated air is air that is holding the absolute maximum amount of water vapor possible at its temperature. Any additional water vapor would condense into liquid water.

Step 3: Combine the definitions. Since saturated air contains the maximum possible amount of water vapor, the actual amount is equal to the maximum possible amount. Therefore, the ratio is 1, which is expressed as 100%.