The narrow capillary section of the tube controls the oil’s flow rate more viscous grades of oil take longer to flow than thinner grades of oil. The suction is then released, allowing the sample to flow back through the tube under gravity. In this method, the oil sample is placed into a glass capillary U-tube and the sample is drawn through the tube using suction until it reaches the start position indicated on the tube’s side. The most common method of determining kinematic viscosity in the lab utilizes the capillary tube viscometer (Figure 1). However, for other oils, such as those containing polymeric viscosity index (VI) improvers, or heavily contaminated or degraded fluids, this relationship does not hold true, and can lead to errors if we are not aware of the differences between absolute and kinematic viscosity.įor a more detailed discussion on absolute versus kinematic viscosity, refer to the article “ Understanding Absolute and Kinematic Viscosity” by Drew Troyer. However, it is the oil’s resistance to flow and shear due to internal friction that is being measured in this example, so it is more correct to say that the gear oil has a higher absolute viscosity than the turbine oil because more force is required to stir the gear oil.įor Newtonian fluids, absolute and kinematic viscosity are related by the oil’s specific gravity. The force required to stir the gear oil will be greater than the force required to stir the turbine oil.īased on this observation, it might be tempting to say that the gear oil requires more force to stir because it has a higher viscosity than the turbine oil. Use the rod to stir the oil, and then measure the force required to stir each oil at the same rate. To measure absolute viscosity, insert a metal rod into the same two beakers. Which one will flow faster from the beaker if it is tipped on its side? The turbine oil will flow faster because the relative flow rates are governed by the oil’s kinematic viscosity. Imagine filling a beaker with turbine oil and another with a thick gear oil. From the results, it can be concluded that the present setup can provide accurate assessment of viscosity of Newtonian fluids and also shows potential for analyzing non-Newtonian fluids at low microliter volumes.An oil’s kinematic viscosity is defined as its resistance to flow and shear due to gravity. Besides, as expected for a viscoelastic fluid, PEG 8000 solutions, the calculated viscosities were found to be less than the reported values due to frequency dependence of storage and loss modulus components of complex viscosity. Minor inconsistencies in the measured resistance and frequency shifts did not affect the results significantly, and were found to be experimental in origin rather than due to electrode surface roughness. The measured viscosities were found to be reproducible and consistent with the values reported in the literature. True frequency shifts, for the purpose of this work, were determined followed by viscosity measurement of aqueous solutions of sucrose, urea, PEG-400, glucose, and ethylene glycol at 25☌☐.5☌. Quartz crystals of 5- and 10-MHz fundamental frequency were calibrated with glycerol-water mixtures of known density and viscosity prior to viscosity measurements. The crystal setup assembly did not impose any unwanted initial stress on the unloaded quartz crystal.
The arrangement was simple with measurement times ranging from 2 to 3 minutes. The technique was based on the principle of electromechanical coupling of piezoelectric quartz crystals. To achieve this, a novel setup was designed that allowed for measurement of viscosity at volumes of 8 to 10 μL. The purpose of this work was to measure viscosity of fluids at low microliter volumes by means of quartz crystal impedance analysis.
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