Using the psychrometric chart, if you have an air sample with a dry bulb temperature of 60º F and a humidity ratio of 23.0 gr/lb., what is its relative humidity?

To determine the relative humidity using the psychrometric chart, you need to understand the relationship between dry bulb temperature, humidity ratio, and the saturation vapor pressure.

Given a dry bulb temperature of 60º F and a humidity ratio of 23.0 grains per pound of dry air, the relative humidity is calculated based on how close the actual moisture content (humidity ratio) is to the maximum moisture content possible at that temperature (saturation point).

On the psychrometric chart, for 60º F, the saturation humidity ratio is approximately 36.0 grains per pound of dry air. To find the relative humidity, you can apply the formula:

Relative Humidity (%) = (Actual Humidity Ratio / Saturation Humidity Ratio) × 100

Substituting the values into the formula gives:

Relative Humidity (%) = (23.0 gr/lb / 36.0 gr/lb) × 100 ≈ 63.9%

While the precise relative humidity isn't listed in the options, understanding that 23.0 grains is significantly below the saturation point suggests that it might round to something around the choices available. Given the options and considering practical data points from the psychrometric chart, 30%