The viscosity is typically reported in centistokes (cSt), equivalent to mm2/s in SI units, and is calculated from the time it takes oil to flow from the starting point to the stopping point using a calibration constant supplied for each tube. This procedure is described in ASTM D445 and ISO 3104.īecause the flow-rate is governed by resistance of the oil flowing under gravity through the capillary tube, this test actually measures an oil’s kinematic viscosity. 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. Symbols, abbreviations, or full names for units of length,Īrea, mass, pressure, and other types.An oil’s kinematic viscosity is defined as its resistance to flow and shear due to gravity. You can find metric conversion tables for SI units, as wellĪs English units, currency, and other data. So 1 millipascal-second = 10 -3 pascal-second.Ĭonversion calculator for all types of measurement units. The SI prefix "milli" represents a factor of Water has a viscosity of 0.0089 poise at 25 ☌, or 1 centipoise at 20 ☌. A centipoise is one millipascal second (mPa centipoise to gram-force second/square centimeterĪ unit of dynamic viscosity in the CGS system of units.centipoise to kilogram-force second/square meter.MPa-s to centipoise, or enter any two units below: Enter two units to convert From: You can do the reverse unit conversion from
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