The wet bulb temperature is the temperature of an object that can be achieved through evaporative cooling, assuming good air flow and that the ambient air temperature remains the same.īy combining the dry bulb and wet bulb temperature in a psychrometric chart or Mollier diagram the state of the humid air can be determined. For the wet bulb, there is a dynamic equilibrium between heat gained because the wet bulb is cooler than the surrounding air and heat lost because of evaporation. The Wet Bulb temperature is always between the Dry Bulb temperature and the Dew Point. The evaporation from the wet muslin is reduced when air contains more water vapor. The rate of evaporation from the wet bandage on the bulb, and the temperature difference between the dry bulb and wet bulb, depends on the humidity of the air. The adiabatic evaporation of water from the thermometer bulb and the cooling effect is indicated by a "wet bulb temperature" lower than the "dry bulb temperature" in the air. Wet Bulb temperature can be measured by using a thermometer with the bulb wrapped in wet muslin. The Wet Bulb temperature is the adiabatic saturation temperature. Constant dry bulb temperatures appear as vertical lines in the psychrometric chart or horizontal lines in the Mollier diagram. The dry-bulb temperature is an indicator of heat content and is shown along the bottom axis of the psychrometric chart or along the left side of the Mollier diagram. The temperature is usually given in degrees Celsius ( oC) or degrees Fahrenheit ( oF). It is called "Dry Bulb" because the air temperature is indicated by a thermometer not affected by the moisture of the air.ĭry-bulb temperature - T db, can be measured using a normal thermometer freely exposed to the air but shielded from radiation and moisture. The Dry Bulb Temperature refers basically to the ambient air temperature. When people refer to the temperature of the air they are normally referring to the dry bulb temperature. The Dry Bulb temperature, usually referred to as "air temperature", is the air property that is most commonly used. The knowledge of only two of these values is enough to determine the state of the moist air - including the content of water vapor and the sensible and latent energy (enthalpy) in the air. The Dry Bulb, Wet Bulb and Dew Point temperatures are important to determine the state of humid air.
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