Viscosity Testing Device

The purpose of viscosity testing is to define a method for measuring the kinematic viscosity of petroleum-based liquids, whether dark or clear. Viscosity is determined by measuring the time it takes for a specific volume of liquid to flow under the influence of gravity through a calibrated viscometer. Dynamic viscosity can then be calculated by multiplying the kinematic viscosity by the density of the fluid.

To perform this test properly, it’s important to understand the key concepts and commonly used equipment, as outlined below.

Key Terms and Equipment

• Density (ρ): The mass per unit volume of a fluid at a given temperature.
• Dynamic Viscosity (η): The ratio of shear stress to shear rate in a fluid. It represents the resistance of a fluid to flow under applied force. The SI unit is Pascal-second (Pa·s).
• Kinematic Viscosity (ν): The ratio of dynamic viscosity to fluid density at the same temperature and pressure.
• Viscometer: A calibrated, glass capillary instrument used to measure the viscosity of liquids within the precision limits set by the standard.
• Glass Thermometers: Use thermometers suited to the desired temperature range. For instance, ASTM110C/IP93C is used for 135°C, while ASTM121C/IP32C is suitable for 100°C. These thermometers must be calibrated with traceable temperature certification by an ISO 17025 accredited lab.
• Digital Contact Thermometer: An electronic device with a digital display and sensor probe used for bath temperature measurement. Annual calibration is required.

In addition to lab instruments, you’ll need paraffin or silicone oil, a viscometer holder, acetone or toluene, and hydrochloric acid for cleaning.

Importance of Viscosity Measurement

Many petroleum-based and non-petroleum substances function as lubricants. Their effectiveness depends largely on having appropriate viscosity. Likewise, the viscosity of fuels is crucial for optimal storage, handling, and performance. Therefore, accurate viscosity determination is a key specification for many products.

Parsian Technology Group offers both single- and dual-bath viscosity testing devices, available in three models: Eco, Pro, and Full. Each unit comes with accessories including a power cable, user manual, warranty card, calibration certificate, vacuum hose, and loading hose.

Performing the Viscosity Test

Principle of Operation

To measure the kinematic viscosity of oils or fluids, a fixed volume of liquid is allowed to flow through the capillary tube of a calibrated viscometer under gravity, while maintaining a constant temperature. Kinematic viscosity is calculated by multiplying the flow time by the viscometer’s calibration constant. The reported viscosity is the average of two acceptable test values.

Device Setup

1. Power On: Connect the power cable and turn on the main switch. The device display will show the main menu.
2. Loading Paraffin (Full model): Press and hold the Pump button to reveal the Load button. Hold it to begin filling the reservoir with paraffin or silicone oil via the corresponding hose.
3. Overflow and Drain Valves: Use the rear valve to drain paraffin. An adjacent overflow valve releases excess paraffin if overfilled (due to expansion when heated).

Test Menu Overview

• Temperature: Current bath temperature.
• Set Point: Target temperature for the fluid in the bath.
• Heater Power: Displays heater usage in percentage.
• Circulation: Indicates the status of the internal pump for uniform temperature distribution.
• T1, T2, T3, T4: Timing values associated with the test, based on viscometer tube constants (F).

Constants (F) are typically supplied with the tube and may vary with temperature.

• Use the Set button to store values and move to the next digit.
• Use + and — to adjust values.
• Press Back to return to the main menu.

Conducting the Viscosity Test

1. In the main menu, press Start to begin the test. The device enters Running mode.
2. Set the bath temperature using the +/– keys (commonly 40°C and 100°C for oils, 135°C for bitumen).
3. Fill the viscometer tube with your sample and wait ~30 minutes for temperature stabilization (thermal equilibrium).
4. In Pro and Full models, use the Vacuum button to move the sample through the tube.
5. To record flow time:

• Press the timing button once at the start (turns green),
• Press again at the endpoint (turns red),
• The time difference (∆T) is used in calculations.

Ending and Printing the Test

After timing is complete:

• Press Stop to finish the test.
• The viscosity value will be displayed.
• In Full models, press Print to print the results.
• Press Back to return to the main menu.

Cleaning the Device

For repeated use:

1. Rinse the viscometer several times with a suitable solvent.
2. Follow up with acetone.
3. Rinse with water and dry by passing filtered dry air through the viscometer for 2 minutes or until no solvent remains.
4. To remove barium salts or mineral residues, use hydrochloric acid before other cleaning steps.

Repeatability (r)

Repeatability refers to the difference between two consecutive viscosity measurements performed by the same operator, in the same lab, under identical conditions. According to inter-laboratory studies:

• For kerosene, diesel, biodiesel, and biodiesel blends at 40°C, the degrees of freedom for repeatability is 16.
• As this does not meet minimum ASTM D6300 criteria, users should apply caution when relying on these repeatability estimates.

Reproducibility (R)

Reproducibility refers to differences between results obtained in different labs by different analysts using the same material under correct conditions.

• For the same fuel types at 40°C, degrees of freedom for reproducibility is 19.
• Since minimum criteria per ASTM D6300 are not met, users should expect variation and plan accordingly.

source: تست ویسکوزیته روغن