INSTRUCTIONS FOR USING THE IRIA INFRARED RADIATION CALCULATOR


The Infrared Radiation Calculator is a convenient way of calculating important quantities used in the design and analysis of radiation measuring and sensing systems. Instructions for calculating specific guantities are described below.

NOTE: This slide rule and these instructions use the earlier notation for radiant exitance, W, instead of the current notation, M.

Conversions of temperatures among Celsius, Kelvin, Fahrenheit, and Rankine scales. Use A, B, L, and M scales. Set the temperature at index mark on one scale and read the corresponding temperature on another. Note the extra index at the left on the N scale to indicate the wavenumber (cm-1) corresponding to {LAMBDAMAX}, the wavelength for the maximum of the blackbody curve. This can be used in calculating the energy of a photon, Ephoton = h(NU). {Plank's constant times the frequency}

Total blackbody radiant exitance, W. Set the temperature of the blackbody source on a temperature scale and read M on the D scale (W/cm2). An emissivity scale (C scale) associated with the D scale permits direct calculation for graybodies. Emissivities of some surfaces are given on the K scale.

Spectral blackbody radiant exitance at peak of blackbody
curve, WLAMBDA_MAX. Set the desired temperature on a temperature scale and read directly from the E scale.

Ratio of WLAMBDA at any wavelength, LAMBDA, to that at LAMBDAMAX, WLAMBDA/ WLAMBDA_MAX.
Set the desired temperature on a temperature scale; then read WLAMBDA/WLAMBDA_MAX from the F scale opposite the desired wavelength on the G scale. Then one can proceed to find the WLAMBDA for the selected wavelength as follows: On the E scale, find the WLAMBDA_MAX for the selected temperature. Then multiply this value by the value of WLAMBDA/WLAMBDA_MAX read from the F scale as noted above.

Blackbody radiation in any spectral interval. Set the temperature scale to the appropriate temperature. Then on the W0-LAMBDA/W0-INFINITY or J scale, read the percentage radiation that lies at wavelengths shorter than LAMBDA2, the longer wavelength interval boundary. Repeat for LAMBDA1, the shorter wavelength interval. boundary, and subtract to obtain percentage of total radiation in the spectral interval. To obtain WDELTA_LAMBDA, total W/cm2for the spectral interval, take this calculated percentage of W, total blackbody radiant exitance as read from D scale. For graybodies, read from D scale for emissivity from C scale.
Irradiance from a 1 cm2 blackody on a surface normal to incoming direction at a given range. Set blackbody temperature. Read irradiance (W/cm2) on V scale for range given in cm. or on W scale for range given in nautical miles.

Conversion among units of total blackoody radiant exitance.
 Use D (W/cm2), P (W/ in2), and Q (Btu-ft-2hr-1) scales. Line up selected value with emissivity of 1.0 on one scale, read converted values at emissivity of 1.0 on other scales.

Transmission coefficient of atmosphere. Use G scale as abscissa for H scale.

Number of photons sec-1cm-2from a blackbody at index temperature. Set temperature on A, B, L, or N scale. Read result at index mark on S scale. Also read photon energy at LAMBDAMAX at index mark on T scale.

Other combinations of the above calculations, as well as useful equations and constants can also be obtained.


NOTE


The Calculator is suitable for approximate calculations. Where precise calculations are required, other procedures should be used.

A noticeable error may occur in the use of the Calculator because of fabricationproblems. The two faces of the calculator may not exactly track each other because of a horizontal shift in the scales on one face with respect to those on the other. Calculations confined to one face need not be corrected. It is therefore preferable to set the selected temperature on the face used in the calculation. If both faces are used in a calculation, the horizontal adjustment can be determined as follows. Set the temperature in Kelvin at 900 K (B scale) and read the Fahrenheit temperature (L scale). It should read 1160 deg. F. The horizontal distance between your reading and 1160 deg. F. is constant in length for all scales.

EXAMPLE OF INFRARED RADIATION CALCULATOR USE


The Infrared Radiation Calculator as pictured in the is set for calculations relating to a surface having a temperature of 900 K (B scale). This corresponds to a temperature of 627 deg. C (A scale), 1160 deg. Fahrenheit scale), 1620 deg. Rankine (M scale).

At this temperature, the total radiant exitance of a blackbody is 3.7 W/cm2 (D scale). This value corresponds to
24.0 W/in2 (P Scale) or 11.8 x l04BTU ft-2hr-1 (Q scale). For an oxidized iron surface (emissivity 0.7, K Scale), the radiant exitance would be 2.55 W/cm2 (D scale).

For the same temperature, a blackbody reaches its peak value of spectral blackbody radiant exitance, WLAMBDA_MAX, at a wave number of 3100 waves cm-1(N scale) or a wavelength of 3.22 micrometers (I scale). The value of WLAMBDA_MAXis 0.75 W/cm2 micrometer -1 (E scale).

At 5.0 micrometers (G scale), the ratio WLAMBDA/WLAMBDA_MAX (F scale) is 0.66. Therefore, the spectral blackbody exitance, WLAMBDA, at 5.0 micrometers is 0.66 x 0.75 or 0.50 W-cm-2 micrometer-1.

What is the total radiant exitance of a 900K blackbody falling in the 3.0 to 5.0 micrometer range? Using the I and J scales, 57% of the total radiant exitance is at wavelengths shorter than 5.0 micrometers, 21% at wavelengths shorter than 3.0 micrometers. The total radiant exitance in the band is therefore (57% - 21%) or 36% of 3.7 W/cm2 (from D scale), or 1.33 W/cm2.

The irradiance from a 1 cm2 blackbody on a surface normal to the incoming direction at a range of l03 cm (10 m) (U scale) is 1.02 x 10-6 W/cm2 (V scale). In the 3.0 to 5.0 micrometer band, it is 36% of this value or 0.367 x 10-6 W/cm2.

The number of photons sec-1-cm-2 from a blackbody at the index temperature is 1.08 x 1020 (S scale). The photon energy at LAMBDAmax is 0.382 electron volt (T scale).
4 September 1990

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