ASTM D381 standard test method for gum content in fuels by jet evaporation
8. Assembly of Air-Jet Apparatus
8.1 Assemble the air-jet apparatus as shown in Fig. 1. With the apparatus at room temperature, adjust the air flow to give a rate of 600 +/- 90 mL/s for the outlet under test. Check the remaining outlets for uniform air flow.
NOTE 3 - A rate of 600 +/- 90 mL/s from each outlet, at room temperature and atmospheric pressure, will ensure delivery of 1000 +/- 150 mL/s at the temperature of 155 +/- 5°C for each outlet. It is recommended to follow the manufacturers' instructions to verify total flow/s (600 mL/s air flow x number of outlets = total flow/s) and uniformity from each outlet.
8.2 Apply heat to the evaporation bath (see 6.4) until the temperature of the bath is between 160 and 165°C. Introduce air into the apparatus at a rate indicated on the flow indicator (see 6.5) from the exercise carried out in 8.1. Measure the temperature in each well with the temperature sensor (see 6.8) placed with the bulb or sensor tip resting on the bottom of the beaker in the well. Do not use any well having a recorded temperature outside the range from 150 to 160°C.
9. Assembly of Steam-Jet Apparatus
9.1 Assemble the steam-jet apparatus as shown in Fig. 1. (Warning - The sample and solvent vapors evaporated during the performance of this test procedure can be extremely flammable or combustible and hazardous from the inhalation standpoint. The evaporation bath must be provided with an effective exhaust hood to control such vapors and reduce the risk of thermal explosion.)
9.2 To place the apparatus in operation, apply heat to the bath. When the temperature reaches 232°C, slowly introduce dry steam into the system until a rate of 1000 +/- 150 mL/s for each outlet is reached (see 10.2). Regulate the temperature of the bath to a range from 232 to 246°C to provide a well temperature of 232 +/- 3°C. Measure the temperature with the temperature sensor, placed resting on the bottom of a beaker in one of the bath wells with the conical adapter in place. Any well having a temperature that differs by more than 3°C from 232°C is not suitable for standard tests.
10. Calibration and Standardization
10.1 Air Flow:
10.1.1 Verify or calibrate the air flow to ensure all outlets meet the 600 +/- 90 mL/s air flow requirement as measured at room temperature and atmospheric pressure. Refer to the instrument manufacturer instructions for specific guidance on performing the air flow calibration procedure. Note the setting of the flow indicator device for use with air and use this setting for subsequent tests.
10.1.1.1 One way to calibrate the air flow is to use a calibrated flow indicator device, such as a flowmeter, separate from the device specified in 6.5, to check the air flow rate at each outlet directly at room temperature and atmospheric pressure. To obtain accurate results, ensure that the back pressure of the flowmeter is less than 1 kPa.
10.1.1.2 Alternatively, another way to calibrate the air flow is to measure and adjust as appropriate the total air flow rate (mL/s) supplied to the outlets. The total air flow rate equals the expected air flow rate at each outlet times the number or outlet positions (for example, instrument has 5 positions and a total air flow rate measurement of 3000 mL/s, indicating an expected air flow rate of 600 mL/s at each outlet). Once verifying the total flow supplied to the outlets is at the appropriate rate, perform uniformity checks by comparing the relative air flow rates at each outlet position versus the requirements in 10.1.1.
10.2 Steam Flow:
10.2.1 Verify or calibrate the steam flow to ensure all outlets meet the 1000 +/- 150 mL/s steam flow requirement. Refer to the instrument manufacturer instructions for specific guidance on performing the steam flow calibration procedure. Note the setting of the flow indicator device for use with steam and use this setting for subsequent tests.
10.2.1.1 One way to calibrate the steam flow, is to attach a copper tube to a steam outlet and extend the tube into a 2-L graduated cylinder that has been filled with crushed ice and water that has been previously weighed. Exhaust the steam into the cylinder for approximately 60 s. Adjust the position of the cylinder so that the end of the copper tube is immersed in the water to a depth of less than 50 mm to prevent excessive back pressure. After the appropriate time has elapsed, remove the copper tube from the cylinder and weigh the cylinder. The gain in mass represents the amount of steam condensed. Calculate the steam rate (mL/s) as follows:
R = (M - m)1000/kt
where:
R = steam rate (mL/s),
M = mass of graduated cylinder with condensed steam, g,
m = mass of graduated cylinder and ice, g,
k = mass of 1000 mL of steam at 232°C at atmospheric pressure = 0.434 g, and
t = condensing time, s.
