# Air - Prandtl Number

** The Prandtl Number ** - Pr - is a * dimensionless number * approximating the ratio of * momentum diffusivity * (kinematic viscosity) to * thermal diffusivity * - and is often used in heat transfer and free and forced convection calculations.

The Prandtl number can for calculations be expressed as

Pr = μ c

_{p}/ k (1)where

μ = absolute or dynamic viscosity [kg/(m s)], [lb_{m}/(ft h)]

c_{p}= specific heat [J/(kg K)], [Btu/(lb_{m}^{o}F)]

k = thermal conductivity [W/(m K)], [Btu/(h ft^{2}^{o}F/ft)]

Below, Prandtl numbers for air at varying temperatures and pressures are given in figures and tables .

See also other properties of ** Air ** at ** varying temperature and pressure: ** Density and specific weight at varying temperature , Density at varying pressure , Diffusion Coefficients for Gases in Air , Specific heat at varying temperature and Specific heat at varying pressure , Thermal Conductivity , Thermal Diffusivity , Properties at gas-liquid equilibrium conditions and Air thermophysical properties at standard conditions and Composition and molecular weight ,

as well as ** Prandtl number ** of Ammonia , Carbon dioxide , Methane , Nitrogen , Propane and Water .

Air Prandtl number at 1 bara pressure, temperature given as °C or °F:

Air Prandtl number at varying temperatures and constant pressures, SI and Imperial units:

Air Prandtl number at 1 bara pressure, temperature given as °C or °F:

Temperature | Pr | Temperature | Pr |
---|---|---|---|

[°C] | [-] | [°F] | [-] |

-100 | 0.734 | -150 | 0.733 |

-50 | 0.720 | -50 | 0.719 |

0 | 0.711 | 0 | 0.714 |

25 | 0.707 | 60 | 0.709 |

50 | 0.705 | 75 | 0.708 |

100 | 0.701 | 100 | 0.706 |

150 | 0.699 | 200 | 0.701 |

200 | 0.698 | 300 | 0.699 |

250 | 0.699 | 400 | 0.698 |

300 | 0.702 | 500 | 0.700 |

Air Prandtl number at given temperatures and 1, 5 10 and 20 bara pressure:

Temperature | Prandtl number at given pressures | |||||
---|---|---|---|---|---|---|

[K] | [°C] | [°F] | 1 bara, 14.5 psia | 5 bara, 72.5 psia | 10 bara, 145 psia | 20 bara, 725 psia |

60 | -213.2 | -351.7 | 4.138 | 4.153 | 4.170 | 4.187 |

80 | -193.2 | -315.7 | 1.7 | 2.252 | 2.259 | 2.269 |

100 | -173.2 | -279.7 | 0.780 | 0.898 | 1.783 | 1.770 |

120 | -153.2 | -243.7 | 0.759 | 0.806 | 0.890 | 1.360 |

140 | -133.2 | -207.7 | 0.747 | 0.773 | 0.812 | 0.923 |

180 | -93.2 | -135.7 | 0.731 | 0.743 | 0.759 | 0.792 |

200 | -73.2 | -99.7 | 0.726 | 0.735 | 0.745 | 0.769 |

220 | -53.2 | -63.7 | 0.721 | 0.728 | 0.736 | 0.754 |

240 | -33.2 | -27.7 | 0.717 | 0.722 | 0.729 | 0.742 |

260 | -13.2 | 8.3 | 0.713 | 0.718 | 0.723 | 0.734 |

273 | 0.0 | 32.0 | 0.711 | 0.715 | 0.720 | 0.729 |

280 | 6.9 | 44.3 | 0.710 | 0.714 | 0.718 | 0.727 |

289 | 15.6 | 60.0 | 0.709 | 0.713 | 0.716 | 0.723 |

300 | 26.9 | 80.3 | 0.707 | 0.711 | 0.714 | 0.722 |

320 | 46.9 | 116.3 | 0.705 | 0.708 | 0.711 | 0.717 |

340 | 66.9 | 152.3 | 0.703 | 0.705 | 0.708 | 0.714 |

360 | 86.9 | 188.3 | 0.701 | 0.703 | 0.706 | 0.711 |

380 | 106.9 | 224.3 | 0.700 | 0.702 | 0.704 | 0.709 |

400 | 126.9 | 260.3 | 0.699 | 0.701 | 0.703 | 0.706 |

500 | 226.9 | 440.3 | 0.698 | 0.700 | 0.701 | 0.703 |

600 | 326.9 | 620.3 | 0.703 | 0.704 | 0.704 | 0.706 |

700 | 426.9 | 800.3 | 0.710 | 0.710 | 0.711 | 0.712 |

800 | 526.9 | 980.3 | 0.717 | 0.718 | 0.718 | 0.719 |

900 | 626.9 | 1160.3 | 0.724 | 0.725 | 0.725 | 0.725 |

1000 | 726.9 | 1340.3 | 0.730 | 0.730 | 0.730 | 0.731 |

1100 | 826.9 | 1520.3 | 0.734 | 0.735 | ||

1500 | 1226.9 | 2240.3 | 0.743 | 0.743 | ||

1900 | 1626.9 | 2960.3 | 0.742 | 0.742 |

## Related Topics

### • Air Psychrometrics

Moist and humid air calculations. Psychrometric charts and Mollier diagrams. Air-condition systems temperatures, absolute and relative humidities and moisture content in air.

### • Fluid Mechanics

The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.

### • Gases and Compressed Air

Properties of air, LNG, LPG and other common gases. Pipeline capacities and sizing of relief valves.

### • Material Properties

Properties of gases, fluids and solids. Densities, specific heats, viscosities and more.

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