Calorimeters total radiation

Radiation. The thermal radiation emitted by a body is a function of the temperature of the body hence, measurement of the radiant energy can be used to indicate the temperature. Commonly employed sensors in this category are optical thermometers, infrared scanners, spectroscopic techniques, and total-radiation calorimeters. 

Radiation thermometers can be sensitive to radiation in all wavelengths (total-radiation thermometers) or only to radiation in a band of wavelengths (spectral-radiation thermometers). Thermocouple and thermopile junctions or a calorimeter are the usual detectors in a total-radiation thermometer. For spectral systems, the classification is normally based on the effective wavelength or wavelength band used—as determined, for example, by a filter, which allows only near-monochromatic radiation to reach the detector, or by the use of a detector sensitive only to radiation in a specific wavelength band. Radiation thermometers utilize the visible portion of the radiation spectrum, infrared thermometers or scanners measure infrared radiation, and spectroscopic thermometers operate with radiation that is normally of shorter wavelength than the other two methods. 

The Ohio State University (OSU) calorimeter (12) differs from the Cone calorimeter ia that it is a tme adiabatic instmment which measures heat released dufing burning of polymers by measurement of the temperature of the exhaust gases. This test has been adopted by the Federal Aeronautics Administration (FAA) to test total and peak heat release of materials used ia the iateriors of commercial aircraft. The other principal heat release test ia use is the Factory Mutual flammabiHty apparatus (13,14). Unlike the Cone or OSU calorimeters this test allows the measurement of flame spread as weU as heat release and smoke. A unique feature is that it uses oxygen concentrations higher than ambient to simulate back radiation from the flames of a large-scale fire. 

Chemical composition was determined by elemental analysis, by means of a Varian Liberty 200 ICP spectrometer. X-ray powder diffraction (XRD) patterns were collected on a Philips PW 1820 powder diffractometer, using the Ni-filtered C Ka radiation (A, = 1.5406 A). BET surface area and pore size distribution were determined from N2 adsorption isotherms at 77 K (Thermofinnigan Sorptomatic 1990 apparatus, sample out gassing at 573 K for 24 h). Surface acidity was analysed by microcalorimetry at 353 K, using NH3 as probe molecule. Calorimetric runs were performed in a Tian-Calvet heat flow calorimeter (Setaram). Main physico-chemical properties and the total acidity of the catalysts are reported in Table 1. 

Two types of calorimeters are used in radiation dosimetry, i.e., the total energy absorption calorimeters (e.g., to determine the energy or power of a particle beam) and thin calorimeters that are partially absorbing and used to measure absorbed dose. The temperature of the calorimeter can be measured either during irradiation (online) or before and after irradiation (ofif-line). 

The heat losses,, need to be discussed next. Obviously, the main heat loss should be through heat conducted by the thermocouples. If the temperature difference between the calorimeter and the surroundings is not exactly equal to zero, this heat loss is given by cEAT (loss a). Another loss comes from the convection of air between calorimeter and surroundings. Again, one can assume that this convection loss is, at least approximately, proportional to the temperature difference AT (loss b). Finally, a fraction of the losses must go through the areas which are not covered by thermocouples — for example, through radiation. This loss, as a catchall, can be assumed to be a certain fraction of the total loss, e (loss c). 

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