Psychrometry  

is the study of the thermodynamic properties of moist air. It is used extensively to illustrate and analyze the characteristics of various air conditioning processes and cyclesOne can also define atmospheric air as a mixture of dry air and water vapor (moisture)Atmospheric air, or moist air is a mixture of many gases and pollutants plus water vapor

Wed Mar 31, 2021

Psychrometry in HVAC

The dry-bulb temperature (DBT)

It is the temperature of air measured by a thermometer freely exposed to the air, but shielded from radiation and moisture.

DBT is the temperature that is usually thought of as air temperature.

It indicates the amount of heat in the air and is directly proportional to the mean kinetic energy of the air molecules.

Temperature is usually measured in degrees Celsius (°C), kelvins (K), or degrees Fahrenheit (°F).

Dry Bulb temperature does not indicate the amount of moisture in the air.

The wet-bulb temperature (WBT)

When unsaturated moist air flows over the wet bulb of the psychrometer, liquid water on the surface of the cotton wick evaporates, and as a result, the temperature of the cotton wick and the wet bulb drops. This depressed wet-bulb reading is called the wet-bulb temperature T and the difference between the dry-bulb and wet-bulb temperatures is called the wet-bulb depression

Wet bulb temperature is the lowest temperature to which air can be cooled by the evaporation of water into the air at a constant pressure

The dew point temperature (DPT)

The dew point is the temperature to which air must be cooled to become saturated with water vapor. When cooled further, the airborne water vapor will condense to form liquid water (dew)

Specific Enthalpy

is the total energy in a system due to pressure and temperature per unit of mass in that system. Specific enthalpy is used in thermodynamic equations when one wants to know the energy for a given single unit mass of a substance. The SI units for specific enthalpy are kJ/kg (kilojoules per kilogram)

h=u+pv

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