Dry Bulb Wet Bulb Relative Humidity Chart

Properties of atmospheric air such as the dry bulb temperature the wet bulb temperature the dew point temperature the specific humidity the relative humidity specific enthalpy and specific volume are discussed in relation to the psychrometric chart below.

Dry bulb wet bulb relative humidity chart. Relative humidity is measured using a device called a sling psychrometer this consists of 2 side by side conventional thermometers one of which the wet bulb thermometer has a wetted wick placed at the bottom the other the dry bulb thermometer has no wetted wick. Example the state of air in the psychrometric chart. 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. Substract wet bulb temperature from the dry bulb temperature i e.

Chart shows dry bulb temperature td in rows and difference between td tw in columns. Determine cell where td. If the air is fully saturated 100 relative humidity the water cannot evaporate so both the wet and dry bulb temperatures are the same. The wet bulb temperature wbt is the temperature read by a thermometer covered in water soaked cloth wet bulb thermometer over which air is passed.

At 100 relative humidity the wet bulb temperature is equal to the air temperature dry bulb temperature. By definition wet bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only. The dry bulb wet bulb and dew point temperatures are important to determine the state of humid air. It includes a dry bulb thermometer a wet bulb thermometer and a psychrometric chart a graph that plots the relationships between the dry and wet bulb temperature relative humidity and dew point at constant pressure.

When the psychrometer is swung around by its attached chain or handle the air causes the water on the wick to evaporate which. If the dry and wet bulb temperatures are set to the same value the calculator will show the saturation mixing ratio the amount of water in saturated air at that temperature. Two independent intensive properties are required to completely specify the state of air in the psychrometric chart. Relative humidity temperature in.

When dry bulb temperature and wet bulb temperature are known we can determine the relative humidity absolute humidity and enthalpy. The following tables calculate dew point and relative humidity based on the observed wet bulb and dry bulb temperatures and the elevation at the site of the observation. At lower humidity the wet bulb temperature is lower than dry bulb temperature because of evaporative cooling. Relative humidity table or relative humidity chart step 1.

The state of air with dry bulb temperature 75 o f and wet bulb temperature 62 5 o f can be visualized in the psychrometric chart as indicated below. The relative humidity is approximately 50 the humidity ratio is approximately 65 grains h2o lb dry air. These can be calculated automatically using wildland fire rh calculator apps for ios and android available for free. Now we are going to learn two of those axis dry bulb temperature and wet bulb temperature.