ASTM D7154 Test Method for Freezing Point of Aviation Fuels (Automatic Fiber Optical Method)
11. Procedure
11.1 Measure out 25 mL +/- 1 mL of the fuel, and transfer it to the clean, dry, test chamber. Support the test chamber in the position recommended by the manufacturer, enclosing the top of the test chamber with a closure assembly supporting the stirrer, temperature measuring device, optical system, and nitrogen purge collar. Adjust the temperature measuring device position, if necessary, so that it is positioned in the center of the test chamber. Ensure that the bottom of the temperature measuring device is between 35 mm to 45 mm from the bottom of the test chamber. Connect the cooling medium inlet and outlet hoses to the respective connections on the test chamber according to the manufacturer's instructions.
11.2 Start the operation of the apparatus according to the manufacturer's instructions. This shall enable the flow of the cooling medium for cooling of the specimen, the flow of the purge gas, and the stirring of the specimen continuously and without interruption. The stirrer shall move up and down vertically at the rate of 1 to 1.5 cycles per second, taking care that the stirrer loops approach the bottom of the test chamber on the downstroke and remain below the specimen surface on the upstroke.
11.3 The fiber optical system shall monitor the specimen for the appearance of hydrocarbon crystals. The apparatus shall disregard any cloud-like formation, due to water, that appears in the test specimen at approximately -10 °C and does not increase in intensity as the specimen temperature decreases.
11.4 After the crystals are detected, the apparatus shall discontinue the flow of the cooling medium. Allow the test specimen to warm by circulating nitrogen gas in place of the cooling medium. The apparatus shall continue the stirring of the specimen in the prescribed manner.
11.5 The fiber optical system shall continue to monitor the hydrocarbon crystals in the specimen and the apparatus shall record the temperature when the crystals completely disappear.
11.6 After the hydrocarbon crystals have disappeared, the apparatus shall discontinue the stirring and the warming medium.
11.7 Remove the test chamber from the apparatus and clean and dry according to the manufacturer's instructions.
