INDEX thermocouple temperature

The luminometer index (ASTM D 1740) is a characteristic that is becoming less frequently used. It is determined using the standard lamp mentioned above, except that the lamp is equipped with thermocouples allowing measurement of temperatures corresponding to different flame heights, and a photo-electric cell to evaluate the luminosity. The jet fuel under test is compared to two pure hydrocarbons tetraline and iso-octane to which are attributed the indices 0 and 100, respectively. The values often observed in commercial products usually vary between 40 and 70 the official specification is around 45 for TRO. 

The still pot is then heated so that the liquid boils gently, and a steady reflux is returned from the head of the column. The jacket temperature is adjusted to correspond to the vapor temperature at the head if a thermometer is used, or it is adjusted to adiabatic operation if a differential thermocouple is employed. The boil-up rate (throughput) is adjusted to a value which is appropriate for the column being used (Table 1-12) by regulating the amount of heat supplied to the still pot. The column is allowed to achieve equilibrium before any material is withdrawn. This is usually determined by the constancy of the vapor temperature or of the refractive index of the material at the column head and usually requires from one-half to several hours. The time necessary for establishing equilibrium is usually greatest for the columns with the highest number of theoretical plates. 

In this small-scale test method, 460-mm (18-in.) x 150-mm (6-in.) wide and up to 25-mm (1-in.) thick vertical sample is used. The sample is exposed to a temperature of 670 + 4 °C at the top from a 300-mm (18-in.) x 300-mm (12-in.) inclined radiant heater with top of the heater closest to and the bottom farthest away from the sample surface. The sample is ignited at the top and flame spreads in the downward direction. In the test, measurements are made for the arrival time of flame at each of the 75-mm (3-in.) marks on the sample holder and the maximum temperature rise of the stack thermocouples. The test is completed when the flame reaches the full length of the sample or after an exposure time of 15-min, whichever occurs earlier, provided the maximum temperature of the stack thermocouples is reached. Flame spread index (7s) is calculated from the measured data, defined as the product of flame spread factor, F, and the heat evolution factor, Q. 

Peetre and Smith used a Varian Model 1400 gas chromatograph with a flame ionization detector, and equipped with an auxiliary thermocouple and temperature guage for the retention index measurements. The temperature could be read to 0.1 and was constant within this range during a measurement. Any significant deviation of the observed temperature from the measurement temperature in the tables was corrected for. 

To aid in the determination of the retention indices of the photolysis products an iron Constantin thermocouple device is used which automatically indicates column oven temperature on the recorder chart during temperature programming. With proper calibration, the column oven temperature is indicated on the chart of a 1 mV recorder and can be read directly in degrees centigrade. A mixture of n-hydrocarbons from n-pentane to /2-pentacosane is chromatographed daily from which a calibration curve of column oven temperature vs Kovats retention index is prepared. The retention indices of eluted compoimds are obtained by graphical comparison of the retention temperature with the calibration curve. 

Thoroughly clean the prism faces as described in 10.2. Adjust the thermostat so that the temperature indicated by the thermocouple placed between the faces of the closed prism (loaded with oil) is within 0.2°C of the desired value. The thermocouple is used for establishing the correct temperature level and may be removed during measurements of refractive index. The observed reading of the thermometer at this temperature must be held constant to 0.02 C in the measurements to follow. 

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