Wet-Bulb Temperature Measurement

Study Notes

As the temperature of the bulb increases, the liquid in the bulb expands and rises in the stem.

Wet-bulb temperature is the temperature of the air as measured by an ordinary thermometer whose glass bulb is covered by a wet cloth or gauze.
Evaporation of water reduces the temperature of the wick, and the resultant temperature is indicated by the mercury in the thermometer stem.
Airflow passing over the wet cloth should have a velocity of at least 15 ft per second.

Humidity ratio is the weight of the water vapor contained in the moist air per unit weight of dry air.
Also known as absolute humidity and specific humidity.

Enthalpy of a dry air-water vapor mixture is the heat content of the moist air per unit weight of dry air above a certain reference temperature.

Specific volume of moist air is defined as the volume per unit weight of dry air.
Specific density of the moist air is equal to the reciprocal of its specific volume.

If the dry-bulb and wet-bulb temperatures are known, the relative humidity can be read from the chart.
If the dry-bulb temperature and relative humidity are known, the wet-bulb temperature can be determined.
If the wet-bulb temperature and relative humidity are known, the dry-bulb temperature can be found.
If the wet-bulb and dry-bulb temperatures are known, the dewpoint can be read from the chart.
If the dry-bulb temperature and relative humidity are known, the dewpoint can be found.

Dry-bulb temperature scale extends along the sole from toe to heel.
Wet-bulb scale extends along the instep from the toe to the top of the shoe.
Condensation or dewpoint is the same as the wet-bulb scale.
Relative humidity lines are located along the side of the shoe and follow approximately the same curve as the instep.
Grains of moisture scale follows along the back of the shoe from the heel to the top.

Psychrometry is the study of the properties of the air.
Knowledge of psychrometry and use of the psychrometric chart are essential for understanding processes involved in drying and storage of grains and other agricultural crops.
Psychrometric chart is a graphic presentation of the conditions or properties of air, such as temperature, humidity, and dewpoint.