4-1.The air and the nitrogen

The air and the nitrogen

Check the performance of the air and nitrogen as the medium to be used in the hot-air drying.

4-1-1.The role of air

Air at room temperature, the atmospheric pressure will behave as a nearly ideal gas.
Density of air ρ [kg / m3] at t [℃], atmospheric pressure P [atm], the water vapor pressure e [atm] ,

The role of air

The advantages and the disadvantages of the air used for hot air heating.

◎ Low cost
◎ Safe into leaks from pipes
◎ Warm the material as a heat source
◎ Reduce the gas boundary layer membrane
◎ Convey the water vapor (carrier gas)
○ Includes several percent water vapor, the effect of water vapor is a positive effect on the direction of air in the normal environment.
○ Oxygen is combined with the aluminum components of the heating coil, acting on the extension of the life of the coil to form a corrosion-resistant coating on the surface.
× Air includes oxygen, which increase oxidation at high temperatures.

4-1-2.The role of nitrogen

The advantages and the disadvantages of the nitorogen used for hot wind heating.

◎ Warm the material as a heat source
◎ Oxygen-free environment is prevent the fire.
◎ Oxygen-free environment is prevent oxidation.
◎ Non-vapor environment is prevent the hydroxyl group or prevent hydrolysis.
◎ Reduce the gas boundary layer membrane
◎ Convey the water vapor (carrier gas)
○ Nitrogen is a relatively safe even if leakage.
× Heating efficiency will be lower by the difference between the room temperature if it to vaporize the liquid nitrogen.
× It is not forming a corrosion-resistant coating on the surface of the heating coil because there is no oxygen, the life of the coil will be shorter as compared to the air

Since nitrogen is non-oxygen, it suits dryness of the inflammable substance containing a solvent.

4-1-3.Density of air

When the air define gas as 4 nitrogen and 1 oxygen, so nitrogen molecular weight 28 and oxygen molecular weight 32, the molecular weight of the air will be 28.8.

Calculation for determining the density of air ( Pressure 1atm, Room temperature 20 ℃ )

Pressure p = 1atm = 101.3×10 ^ 5Pa
Temperature t = 273 + C
Air V = 1m ^ 3
Number of moles n = mol
Gas constant R = 8.31J / mol · K
Ideal gas equation = pV = nRT
Density of air ρ =

n = pV/RT = 1.103x10^5Pa x 1m^3 / 8.31J/mol・K x (273+20)K = 41.6mol

ρ= (28.8 x 41.6)g/m^3 = 1200g/m^3 = 1.2g/ℓ

4-1-4.Characteristics List

Constituents of air

Component Chemical formula Volume ratio percentage Mass ratio Gaseous density Specific gravity
Nitrogen N2 78.084 0.75520000 1.251 1.105
Oxygen O2 20.9476 0.23150000 1.429 0.967
Argon Ar 0.934 0.01280000 1.78 1.38
Carbon dioxide CO2 0.039 0.00046000 1.977 1.54
Neon Ne 0.001818 0.00001200 0.9002 0.69
Helium He 0.000524 0.00000072 0.1785 0.13
Methane CH4 0.000181
Krypton Kr 0.000114
Sulfur dioxide SO2 0.0001
Hydrogen H2 0.00005
Dinitrogen monoxide N2O 0.000032
Xenon Xe 0.0000087
Ozone O3 0.000007
Nitrogen dioxide NO2 0.000002
Iodine I2 0.000001

Outline air composition

Component Chemical formula Volume ratio percentage Mass ratio
Nitrogen N2 0.79 0.768
Oxygen O2 0.21 0.232

Characteristics of the constituents of the air

Component Van der Waals constant Molecular weight Gas constant Specific heat at constant pressure Specific heat at constant volume Specific heat ratio
  a / Pa m6 mol−2 b / m3 mol−1 g/mol R (J/g・K) Cp (J/g・K) Cv (J/g・K) γ
Air 135 × 10−3 36.6 × 10−6 28.967 0.28703 1.005 0.718 1.399
Nitrogen(N2) 141 × 10−3 39.2 × 10−6 28.013 0.29680 1.039 0.743 1.399
Oxygen(O2) 138 × 10−3 31.9 × 10−6 31.999 0.25984 0.914 0.654 1.398
Water vapor (H2O) 553 × 10−3 33.0 × 10−6 18.015 0.46152 4.186 3.147 1.33
Helium(He) 3.45 × 10−3 23.8 × 10−6 4.003 2.07727 5.240 3.16 1.66
Argon (Ar) 136 × 10−3 32.2 × 10−6 39.948 0.20813 0.523 0.32 1.68
Hydrogen(H2) 24.8 × 10−3 26.7 × 10−6 2.016 4.12449 14.250 10.12 1.408
Carbon monoxide(CO) 151 × 10−3 40.0 × 10−6 28.010 0.29684 1.041 0.74 1.4
Carbon dioxide(CO2) 365 × 10−3 42.8 × 10−6 44.010 0.18892 0.819 0.63 1.3
Ammonia(NH3) 422 × 10−3 37.1 × 10−6 17.031 0.48821 2.060 1.57 1.31
Methane(CH4) 238 × 10−3 42.8 × 10−6 16.042 0.51828 2.160 1.63 1.32
*0℃/1atm
The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Kelvin.

The characteristics of the air

Temperature conditions Density Specific heat at constant pressure Coefficient of viscosity Kinematic viscosity Thermal conductivity Thermal diffusivity Prandtl number
T ρ Cp η ν λ α Pr
K kg/m3 kJ/(kg・K) μPa・s mm2/s mW/(m・K) mm2/s
100 3.6109 1.072 7.1 1.97 9.22 2.38 0.826
200 1.7679 1.009 13.4 7.58 18.1 10.15 0.747
300 1.1763 1.007 18.62 15.83 26.14 22.07 0.717
400 0.8818 1.015 23.27 26.39 33.05 36.93 0.715
500 0.7053 1.031 27.21 28.58 39.51 54.33 0.71
600 0.5878 1.052 30.78 52.36 45.6 73.7 0.71
700 0.5038 1.076 34.1 67.7 51.3 94.6 0.715
800 0.4408 1.099 37.23 84.5 56.9 117 0.719
900 0.3918 1.122 40.22 102.7 62.5 142 0.722
1000 0.3527 1.142 43.08 122.1 67.2 167 0.732
1100 0.3206 1.16 45.84 143 71.7 193 0.742

 

Guide to the Optimal Heater

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