Friday 7 September 2007

Air Humidifying with Steam - Imperial Units

The amount of vapor (lb/h in 100 cfm) in humid air


The table below can be used to calculate the amount of steam needed to humidify 100 cfm (cubic feet per minute) air.

Vapor in 100 cfm air (lb/h)
Dry
Temperature
(oF)
Humidity (%)
100 85 80 75 70 65 60 55 50 45 40 35 30
90 12.84 10.92 10.26 9.6 9 8.34 7.68 7.08 6.42 5.78 5.14 4.49 3.85
88 12.06 10.26 9.66 9.06 8.46 7.87 7.26 6.66 6.06 5.41 4.82 4.22 3.62
86 11.4 9.66 9.12 8.52 7.98 7.38 6.85 6.3 5.7 5.13 4.56 3.99 3.42
85 11.04 9.36 8.82 8.28 7.74 7.2 6.6 6.06 5.52 4.97 4.42 3.86 3.31
84 10.68 9.06 8.52 7.98 7.5 6.96 6.42 5.87 5.34 4.81 4.27 3.74 3.2
83 10.38 8.82 8.34 7.8 7.26 6.72 6.24 5.71 5.19 4.67 4.15 3.63 3.11
82 10.08 8.58 8.04 7.56 7.08 6.54 6.06 5.54 5.04 4.54 4.03 3.53 3.02
81 9.78 8.34 7.8 7.32 6.84 6.36 5.87 5.38 4.89 4.4 3.91 3.42 2.93
80 9.48 8.04 7.56 7.08 6.66 6.18 5.69 5.21 4.74 4.27 3.79 3.32 2.84
79 9.18 7.8 7.32 6.9 6.42 5.96 5.51 5.05 4.59 4.13 3.67 3.21 2.75
78 8.88 7.56 7.08 6.66 6.24 5.77 5.33 4.88 4.44 3.99 3.55 3.11 2.66
77 8.64 7.32 6.9 6.48 6.06 5.62 5.18 4.75 4.32 3.89 3.46 3.02 2.59
76 8.4 7.14 6.72 6.3 5.88 5.46 5.04 4.62 4.2 3.78 3.36 2.94 2.52
75 8.1 6.9 6.48 0.06 5.67 5.26 4.86 4.48 4.05 3.64 3.24 2.83 2.43
74 7.86 6.66 6.3 5.89 5.5 5.11 4.72 4.32 3.93 3.53 3.14 2.75 2.36
73 7.62 6.48 6.12 5.71 5.33 4.95 4.57 4.12 3.81 3.43 3.05 2.66 2.29
72 7.38 6.3 5.9 5.53 5.17 4.79 4.43 4.06 3.69 3.32 2.95 2.58 2.21
71 7.14 6.06 5.71 5.35 4.99 4.64 4.29 3.93 3.57 3.21 2.86 2.5 2.14
70 6.9 5.86 5.52 5.17 4.84 4.48 4.14 3.79 3.45 3.1 2.76 2.41 2.07
69 6.72 5.71 5.38 5.04 4.7 4.37 4.03 3.7 3.36 3.02 2.67 2.35 2.02
68 6.48 5.51 5.18 4.86 4.54 4.21 3.89 3.55 3.24 2.92 2.59 2.27 1.94
67 6.24 5.3 4.99 4.68 4.37 4.06 3.74 3.43 3.12 2.81 2.5 2.18 1.87
66 6.06 5.15 4.85 4.54 4.24 3.94 3.64 3.33 3.03 2.72 2.42 2.12 1.82
65 5.87 4.99 4.7 4.4 4.11 3.82 3.52 3.23 2.93 2.65 2.35 2.06 1.76
60 4.97 4.23 3.98 3.73 3.48 3.23 2.98 2.74 2.48 2.24 1.99 1.74 1.49
55 4.19 3.56 3.35 3.14 2.93 2.72 2.51 2.31 2.09 1.89 1.68 1.47 1.26
50 3.52 2.99 2.82 2.64 2.47 2.29 2.11 1.94 1.76 1.58 1.41 1.23 1.06
45 2.95 2.51 2.36 2.21 2.06 1.92 1.77 1.62 1.47 1.33 1.18 1.03 0.89
40 2.45 2.09 1.96 1.84 1.72 1.6 1.47 1.35 1.22 1.1 0.98 0.86 0.74
30 1.67 1.42 1.33 1.25 1.17 1.09 1 0.92 0.83 0.75 0.67 0.58 0.5
20 1.07 0.91 0.85 0.8 0.75 0.7 0.64 0.59 0.53 0.48 0.43 0.37 0.32
10 0.67 0.56 0.53 0.5 0.47 0.43 0.4 0.37 0.33 0.3 0.26 0.23 0.2
0 0.41 0.35 0.32 0.31 0.29 0.26 0.25 0.22 0.2 0.19 0.16 0.13 0.12
-10 0.25 0.21 0.2 0.19 0.17 0.16 0.15 0.14 0.12 0.11 0.1 0.08 0.08
-20 0.14 0.12 0.11 0.11 0.1 0.1 0.08 0.08 0.72 0.06 0.05 0.05 0.04

Example - Humidifying Air with Steam

How much steam is needed to transform air at 30oF with 100% humidity to air at 70oF and 40% humidity?

In air at 30oF and 100% humidity, the steam content is 1.67 lb/h (100 cfm/h air flow).

At air 70oF and 40% humidity, the steam content is 2.76 lb/h (100 cfm/h air flow).

The difference (2.76 - 1.67) = 1.09 lb/h is the amount of steam necessary for 100 cfm/h air flow.

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Related Topics

  • Air Psychrometrics Air psychrometrics are the study of moist and humid air and the change in air conditions. Psychrometric charts, Mollier diagrams, air temperature, absolute and relative humidity, moisture content ...
  • Steam and Condensate Steam & condensate properties, capacities, pipe sizing and systems configuration. Steam is an essential part of modern industrial process technology. Without steam, food, textile, chemical, medical, power, heating and transport industries could not perform as they do. In this section you will find tools and information regarding steam and condensate applications.

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Air Composition

Dry air is a mechanical mixture of nitrogen, oxygen, carbon dioxide and more

Air is a mixture of gases, 78% nitrogen and 21% oxygen with traces of water vapor, carbon dioxide, argon, and various other components. We usually model air as a uniform (no variation or fluctuation) gas with properties that are averaged from all the individual components.

Gas Ratio compared to Dry Air (%) Molecular Mass
- M -
(kg/kmol)
Chemical Symbol Boiling Point
By volume By weight K (oC)
Oxygen 20.95 23.20 32.00 O2 90.2 -182.95
Nitrogen 78.09 75.47 28.02 N2 77.4 -195.79
Carbon Dioxide 0.03 0.046 44.01 CO2 194.7 -78.5
Hydrogen 0.00005 ~ 0 2.02 H2 20.3 -252.87
Argon 0.933 1.28 39.94 Ar 84.2 -186
Neon 0.0018 0.0012 20.18 Ne 27.2 -246
Helium 0.0005 0.00007 4.00 He 4.2 -269
Krypton 0.0001 0.0003 83.8 Kr 119.8 -153.4
Xenon 9 10-6 0.00004 131.29 Xe 165.1 -108.1

The water or vapor content in air varies. The maximum moisture carrying capacity of air depends primarily on the temperature.

The composition of air is unchanged until the height of approximately 10.000 m.

The average air temperature diminishes at the rate of about 0.6oC for each 100 m vertical height

"One Standard Atmosphere" is defined as the pressure equivalent to that exerted by a 760 mm column of mercury at 0oC sea level and at standard gravity (32.174 ft/sec2).

Common Pressure Units frequently used as alternative to "one Atmosphere"

  • 76 Centimeters (760 mm) of Mercury
  • 29.921 Inches of Mercury
  • 10.332 Meters of Water
  • 406.78 Inches of Water
  • 33.899 Feet of Water
  • 14.696 Pound-Force per Square Inch
  • 2116.2 Pounds-Force per Square Foot
  • 1.033 Kilograms-Force per Square Centimeter
  • 101.33 Kilopascal

More about Temperature, Density, Specific heat, Thermal Conductivity - the properties of air.

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Related Topics

  • Air Psychrometrics Air psychrometrics are the study of moist and humid air and the change in air conditions. Psychrometric charts, Mollier diagrams, air temperature, absolute and relative humidity, moisture content ...
  • Material Properties Material properties as densities, heat capacities for gases, fluids and solids ....

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  • Air Properties Air properties - temperature, density, specific heat, thermal conductivity, expansion coefficient, kinematic viscosity and Prandtl number for temperatures between -150oC and 400oC.
  • Specific Heat Ratio of Air Specific Heat Ratio of air at temperatures from -40 to 1.000oC (-40 to 1.500oF) at standard atmospheric pressure - in Imperial and SI Units
  • Humid Air and the Ideal Gas Law The Ideal Gas Law relating pressure, temperature, and volume of an ideal or perfect gas can also be used for air with water vapor - moist air
  • Molecular Mass of Air Dry air is a mixture of gases where the molecular weight can be calculated by adding the weight of each component
  • Density of Dry Air, Water Vapor and Moist Humid Air Calculating the density of dry air, water vapor or the mixture of air and water vapor - moist or humid air
  • Dry Air Properties Dry air properties at temperatures ranging 175 - 1900 K - specific heat capacity, ratio of specific heats, dynamic viscosity, thermal conductivity, Prandtl number, density and kinematic viscosity
  • Nitrogen - Specific Heat Capacity Specific heat capacity of Nitrogen Gas - N2 - at temperatures ranging 175 - 6000 K
  • Oxygen - Specific Heat Capacity Specific heat capacity of Oxygen Gas - O2 - at temperatures ranging 175 - 6000 K
  • Ideal Gas Properties Oxygen Enthalpy, Internal Energy and Entropy of Oxygen

Air - Altitude, Density and Specific Volume

The density and the specific volume of air varies with the elevation above sea level

The density of air will vary with the pressure (the Ideal Gas Law) and the altitude above sea level. Mean absolute pressure at sea level is approximately 760 mmHg (101.325 kPa, kN/m2) with a variation is about +/- 5%.

Altitude and Air Pressure

The air pressure varies with altitude as shown in the table below:

Altitude
(m)
Barometer
(mmHg)
0 749
75 743
150 735
250 726
300 723
450 709
600 695
750 681
900 668
1,000 658
1,200 643
1,350 632
1,500 620
1,800 598
2,100 577
2,400 555

Altitude and Air Density

Air density and specific volume as functions of altitude above sea level are indicated in the diagrams below:

air altitude meters density and specific volume diagram

air altitude feet density and specific volume diagram

STP - Standard Temperature and Pressure

  • STP - Standard Temperature and Pressure is 0oC and 101.325 kN/m2.

NTP - Normal Temperature and Pressure

  • NTP - Normal Temperature and Pressure, commonly used for testing and documentation of fan capacities, is 20oC and 101.6 kN/m2 (60oF , 30 in Hg)

Altitude and Specific Volume Correction

The specific volume of standard air at a certain altitude can be calculated by multiplying with the volume correction factor below

Altitude Volume Correction Factor
(m) (ft)
0 0 1.00
480 1600 1.05
990 3300 1.11
1500 5000 1.17
1980 6600 1.24
2460 8200 1.31
2970 9900 1.39

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Related Topics

  • Air Psychrometrics Air psychrometrics are the study of moist and humid air and the change in air conditions. Psychrometric charts, Mollier diagrams, air temperature, absolute and relative humidity, moisture content ...
  • Fluid Mechanics The study of fluids - liquids and gases. Involves various properties of the fluid, such as velocity, pressure, density and temperature, as functions of space and time.
  • Gas and Compressed Air Gas properties, capacities, sizing ...
  • Material Properties Material properties as densities, heat capacities for gases, fluids and solids ....
  • Ventilation Systems for ventilation and air handling.

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