ASTM D7154 Test Method for Freezing Point of Aviation Fuels (Automatic Fiber Optical Method)
6. Apparatus (see Annex A1)
6.1 Automatic Fiber Optical Apparatus - The apparatus as described in Annex A1 shall consist of a test chamber comprising a jacketed test tube supported in a jacketed enclosure configuration that is capable of cooling and heating the test specimen to the temperatures required in the test. The apparatus shall have a nitrogen purge collar as part of the closure assembly for the test chamber, which prevents moisture from combining with the test specimen. The apparatus shall be capable of measuring the temperature of the test specimen, continuously stirring the test specimen at the prescribed rate, automatically cooling and then heating the test specimen, monitoring the test specimen with an electronic optical system for appearance and disappearance of the crystals in the test specimen under the conditions of the test, and recording the appearance and disappearance temperatures.
6.2 Circulating Bath, refrigeration unit equipped with a circulating pump capable of maintaining the temperature of a quantity of methyl alcohol at least 20 °C lower than the minimum test specimen temperature expected.
NOTE 3 - To achieve a typical test chamber cooling condition of -75 °C, the circulating bath should be capable of achieving -85 °C to -90 °C, since approximately 5 °C to 10 °C is consumed in the circulation lines and insulation.
6.3 Instrument and Software Version - The HCP 860 apparatus with V.22 software was used in the 2003 Interlaboratory Program that determined the precision and relative bias in Section 13.
7. Reagents and Materials
7.1 Cooling Medium, Methyl Alcohol - A commercial or technical grade of anhydrous methanol is suitable for use as the cooling medium. (Warning - Extremely flammable. Toxic. May be fatal or cause blindness if swallowed or inhaled.)
7.2 Nitrogen Gas, dry nitrogen gas which has a dew point below the lowest temperature expected to be attained by the test specimen under the conditions of the test. (Warning - Compressed gas under high pressure. Inert gas can be an asphyxiant when inhaled.)
7.3 Cleaning Solvents, suitable for cleaning and drying the test chamber, such as petroleum naphtha and methyl alcohol. (Warning - Flammable. Liquid causes eye burns. Vapor harmful. Toxic. May be fatal or cause blindness if swallowed or inhaled.)
8. Sampling
8.1 Obtain a sample in accordance with Practice D4057 or D4177.
8.2 At least 25 mL of sample is required for each test. Refer to Practice D4057.
9. Preparation of Apparatus
9.1 Prepare the apparatus for operation in accordance with the manufacturer's instructions.
9.2 Clean and dry the test chamber with petroleum naphtha to rinse out any previous specimen followed by a second rinse of alcohol to remove naphtha. Dry with moisture-free air or gas. Ensure that moisture does not remain inside the test chamber.
9.3 Prepare the refrigerated circulating bath for operation in accordance with the manufacturer's instructions and allow it to attain a temperature lower than -75 °C. The temperature of the alcohol, at the test chamber, shall not be below -80 °C unless the expected freezing point is below -60 °C.
9.4 Confirm that the supply of nitrogen purge gas is connected and regulated in accordance with the manufacturer's instructions.
10. Calibration and Standardization
10.1 Ensure that all of the manufacturer's instructions for calibrating, checking, and operating the apparatus are followed including calibration of the temperature measuring system against a certified standard temperature device.
10.2 A sample with a mutually agreed upon freezing point such as one from an interlaboratory test program, Test Method D2386 or equivalent, can be used to verify performance of the apparatus within the precisions of this test method.
