Chromel-alumel thermocouples. temperature range

Temperature measurements ranging from 760 to 1760°C are made usiag iron—constantan or chromel—alumel thermocouples and optical or surface pyrometers. Temperature measuriag devices are placed ia multiple locations and protected to allow replacement without iaciaerator shutdown (see... 

According to procedure published previously the cylindrical samples were heated by friction during sample rotation [1], Hard alloy blocks being pressed to sample surface were used for friction process. Friction treatment was held either in Ar-gas (FT) or in ammonia medium (FN). The temperature of sample ranged from 773 to 853K was controlled by chromel-alumel thermocouple. Duration of treatment was about to 60 min. After FT and FN processes the sample surface was smooth similar to that of original polished one. 

The sample is lowered into the reaction zone by an electric motor-driven windlass at about 1/2 inch/sec. The position of the sample in the reactor is obtained by monitoring the output of a small 10-tum potentiometer which is coupled directly to the windlass. Temperatures in the reactor are measured by stainless steel-encased chromel-alumel thermocouples, the closest one to the sample being located 1/4 inch below the sample. Hydrogen flow rates are controlled 5% over the range 10-40 scf/hr. Gas analysis is obtained by splitting a portion of the gas product stream to an infrared detector where methane content is continuously measured and a portion to a gas chromatograph where total gas composition is determined. 

The reactors used were 1.09 cm I.D. and about 80 cm long, and 45.7 cm (equivalent to 42.8 cc) of the reactor was positioned Inside a Hoskins electric furnace, type FC-301. The ends of the furnace were Insulated with fire brick. Five chromel-alumel thermocouples were attached to the outer surface of the reactor at various positions. Temperature variations along the reactor were In general less than 90°C when the temperature was controlled In the 700 to 900 C range. The temperatures reported In the result section are the maximum teirperatures for the various runs. 

Thermocouples are based on the thermoelectric Seebeck effect, which generates a voltage at the junction between two metallic conductors, which depends on temperature [13]. Thus, in the measuring circuit, two junctions are created, namely, a sensitive (or hot) junction at the point where temperature has to be measured and a nonsensitive (cold) junction, kept at a constant known temperature, where the voltage established between the conductors can be easily measured [19]. Different typologies of thermocouples exist for application in a wide range of conditions they essentially differ by the materials, the most common being J (iron/constantan), K (chromel/alumel), T (copper/constantan), and E (chromel/constantan). 

The operating temperature range is typically 100 -1000 K using samples of area 30-50 mm and thickness 0.01-0.3 mm. The temperature resolution is 0.0025 K for T< 770 K and 0.025 K for r> 770 K. The sample holder is purged with a dry inert gas. Alumel-chromel or chromel-constantan thermocouples of 0.002 mm diameter are placed in a paper frame and soldered to metal samples to measure. Polymers are dissolved in an organic solvent and the solution is spread on a thin metal... 

Temperature measurements. Temperatures in the range of 800 to 1300°F are commonly measured with Chromel-Alumel or platinum-platinum-rhodium thermocouple.s. The accuracy and life of a thermocouple in the temperature range of interest arc functions of the wire size and, in general, the largest possible thermocouple should be used. Either beaded thermocouples or the newer, magnesium oxide-insulated thermocouples may be used. 

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