Airstream Density Calculator
Airstream Density Calculator
Determines airstream density at the fan inlet from inlet temperature, atmospheric pressure, fan inlet static pressure and airstream moisture.
Results
| Density factor, elevation (dfe) | 1.000 | |
|---|---|---|
| Density factor, pressure (dfp) | 1.000 | |
| Density factor, temperature (dft) | 1.000 | |
| Density factor, moisture (dfm) | 1.000 | |
| Density factor (df) | 1.000 |
| Humid volume | 13.33 | ft³ mix/lbm dry air |
|---|---|---|
| Moist air enthalpy | 16.8 | Btu/lbm dry air |
Calculator notes and assumptions
Application
This calculator is for dry air having an isentropic exponent of 1.4 with the addition of various amounts of water (moisture) in vapor phase. It is not applicable to other gases or condensibles.
Fan inlet temperature units and entry
All temperatures are airstream temperatures at the fan inlet and in degrees Fahrenheit (°F). Enter temperatures as actual (gauge) values and not in absolute values.
Absolute temperature used for calculations is 530 °R.
Dry bulb temperature is the temperature measured directly by a thermometer or other direct temperature sensing device.
Wet bulb temperature is the temperature at which water (as a liquid) brings the air to saturation adiabatically and at the same temperature. It can be measured by wrapping a wettable material (fabric) around the bulb of a dry bulb thermometer and moving the airstream across the wetted material at 1,000 fpm or higher. The wet bulb temperature is the temperature at which the thermometer temperature reading first stabilizes.
Atmospheric pressure units and entry
When working on the basis of site elevation, enter as feet above sea level (ft-asl). If unknown, common practice is to use the elevation listed by either the closest local airport or National Weather Service Forecast site.
When working on the basis of barometric pressure, enter the site actual barometric pressure in inches of mercury (in. Hg). If a local barometric pressure gauge is not available or useable, common practice is to use the barometric pressure listed at the closest local airport or National Weather Service Forecast site.
Fan inlet (duct) pressure units and entry
All pressures are in inches of water gauge (in. wg, or Pg) and as measured at the fan inlet.
Enter pressures as actual gauge pressure values using + (positive) or − (negative) to indicate above or below standard atmospheric pressure. Do not enter absolute values.
Absolute pressure used for calculations is 407 inches water gauge.
Airstream moisture
Enter the water vapor moisture content as either Relative Humidity (ø) or Specific Humidity (ω).
When using Relative Humidity (ø), enter as a percentage (%). Relative Humidity is the ratio of the actual partial pressure of the water vapor in air to its saturation pressure at a corresponding dry bulb temperature. If the airstream enters the system from ambient conditions and no work is done on the airstream to change its Relative Humidity (change in temperature, pressure, etc.), then acceptable practice is to use the Relative Humidity listed at the closest local airport or National Weather Service Forecast site.
When using Specific Humidity (ω), enter as pounds of water vapor per pound of dry air (lbm-water vapor/lbm-dry air). Specific Humidity may sometimes be listed in units of grains-water vapor instead of lbm-water vapor, in which case it should be converted to lbm-water vapor. The common unit conversion is 7,000 grains = 1 lbm.
Specific Humidity is sometimes referenced as the airstream Humidity Ratio, Moisture Content, or Mixing Ratio.
