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What are the units of viscosity? What is the conversion relationship?

It is best to give a definition of viscosity first:

When the fluid is flowing, there is relative motion between adjacent fluid layers, and frictional resistance will be generated between the two fluid layers, which is called viscous force. Viscosity is a physical data used to measure the magnitude of viscous force. Its size is determined by factors such as substance type, temperature and concentration.

Viscosity is generally the abbreviation of dynamic viscosity, and its unit is Pa·s (Pa·s) or milliPa·s (mPa·s). Viscosity is divided into dynamic viscosity, kinematic viscosity and relative viscosity. The three are different and should not be confused.

Viscosity can also be measured with Tu-4 or Tu-1 cup in seconds (s).

The symbol for (dynamic) viscosity is μ and the unit is Pascal seconds (Pa s)

It is defined by the following formula: L=μ·μ0/h

μ0——the speed of the plate in its own plane when it moves parallel to a fixed flat wall

h——The distance from the flat plate to the fixed flat wall. However, this distance should be small enough so that the flow of the fluid between the flat plate and the fixed flat wall is laminar

L——The fluid friction force acting on the unit area of ​​the plate during the movement of the plate

The symbol of kinematic viscosity is v, and kinematic viscosity is the ratio of the dynamic viscosity of a substance to its density in engineering calculations, and its unit is: (m2/s). The unit is the square meter per second (m2/s)

v=μ/p

Viscosity has dynamic viscosity, its unit: Pascal seconds (Pa s); in the petroleum industry, "En's viscosity" is also used, which is not the viscosity concept introduced above. Rather, it is the reading of the fluid measured directly in the Engela viscometer.

Viscosity measurement methods are divided into two categories: absolute viscosity and relative viscosity. Absolute viscosity is divided into two kinds of dynamic viscosity and kinematic viscosity; relative viscosity has Enzler viscosity, Saybolt viscosity and Reid viscosity and so on.

1. The dynamic viscosity η takes two areas of 1m2 in the fluid, the distance is 1m, and the resistance generated when the relative moving speed is 1m/s is called the dynamic viscosity. The unit is Pa.s (Pa.s). The unit of dynamic viscosity used in the past is poise or centipoise, and poise or centipoise are not legal units of measurement.

1Pa.s=1N.s/m2=10Ppoise=103 power cp=1Kcps

ASTM D445 standard stipulates that kinematic viscosity is used to calculate dynamic viscosity, that is, η=ρ.υ where η-dynamic viscosity, Pa.s period target system ρ-density, kg/m3 υ-kinematic viscosity, m2/s my country National Standard GB/T506-82 is a low temperature dynamic viscosity determination method for lubricating oil. This method is used to determine the low temperature (0～-60℃) dynamic viscosity of lubricating oil and dark petroleum products. Under strictly controlled temperature and different pressure conditions, determine the time required for a certain volume of sample to flow through a capillary viscometer with a calibrated constant, in seconds. Calculate the dynamic viscosity from the product of the time the sample flows through the capillary, the calibration constant of the capillary and the average pressure, and the unit is Pa.s. The difference between the two results of the repeated determination of this method should not exceed ± 5% of the arithmetic mean.

2. Kinematic viscosity υ The ratio of the dynamic viscosity η of the fluid to the density ρ of the fluid at the same temperature is called the kinematic viscosity. It is a measure of the resistance of this fluid to flow under the force of gravity. In the International System of Units (SI), the unit of kinematic viscosity is m2/s. In the past, centistokes (cSt) were usually used as a unit of kinematic viscosity, which was equal to 10-6m2/s, (ie 1cSt=1mm2/s.

Kinematic viscosity is usually measured with a capillary viscometer. Under strict temperature and reproducible driving pressure, measure the time for a certain volume of liquid to flow through the calibrated capillary under the action of gravity. In order to measure the kinematic viscosity, the temperature of the fluid to be measured must be controlled first, and the temperature measurement accuracy is required. Reach 0.01 °C; secondly, the appropriate size of the capillary must be selected to ensure that the outflow time is neither too long nor too short, that is, thicker capillaries are used for viscous liquids, and thinner capillaries are used for thinner liquids. The flow time should not be less than 200 seconds; the constant of the viscometer must be calibrated regularly; and the viscometer must be installed vertically. The national standard for kinematic viscosity is GB/T256-88, which is equivalent to ASTM D445-96/IP71/75.

3. Enzl viscosity OE my country's national standard is the Enzl viscosity determination method for petroleum products GB/T266-88. This is a relative viscosity commonly used in the past, which is defined as the time (s) required for 200ml of liquid to flow through Enz at a specified temperature, and the time (s) required for the same volume of distilled water to flow through Enz at 20°C The ratio is called Enz viscosity.

4. Redwood viscosity (Redwood) This viscosity is mainly used in the United Kingdom and Japan. It is defined as the time required for 50ml of test oil to flow through the Rays at a specified temperature of 60°C or 98.9°C, in seconds.

5. Saybolt Universal Viscosity (Saybolt Universal Viscosity) The United States is often used to this viscosity unit, which is defined as the time required to flow out 60ml of liquid from Saybolt at a specified temperature, in seconds. American Standard Method is ASTM D88

6. Conversion of several viscosities 1) Conversion of Ennst viscosity and kinematic viscosity

Kinematic viscosity υ (mm2/s)=7.310E-6.31/0E 2) Conversion of Reinhardt viscosity and kinematic viscosity Kinematic viscosity υ (mm2/s)=0.26R-172/R When R