throttling device

There are three methods for measuring dynamic viscosity, kinematic viscosity, and conditional viscosity. 　　(1) Dynamic viscosity: ηt is the resistance generated when two liquid layers separated by 1 centimeter, each with an area of 1 square centimeter, move relative to each other at a speed of 1 centimeter per second; its unit is grams per centimeter-second. 1 gram/cm·second = 1 poise. Generally, poise is used as the unit for dynamic viscosity in industry. 　　(2) Kinematic viscosity: At a temperature of t°C, kinematic viscosity is denoted by the symbol γ. In the International System of Units, its unit is the stoke, which is equivalent to m2/s. In practical measurements, centistokes are commonly used; 1 centistoke equals 1 mm2/s. Kinematic viscosity is widely used to determine the viscosity of liquid petroleum products such as jet fuel, diesel, and lubricating oils, as well as of dark-colored petroleum products, used lubricating oils, and crude oil. The determination of kinematic viscosity is carried out using the counter-current method. (3) Conditional viscosity: refers to the viscosity measured using different specific viscometers and expressed in conditional units. The three most commonly used conditional viscosities in various countries are as follows: ① Engler viscosity, also known as Engler viscosity. It is the ratio of the time required for a certain amount of sample to flow 200 milliliters from an Engler viscometer at a specified temperature (such as 50°C, 80°C, 100°C) to the time required for distilled water to flow the same volume at 20°C, expressed in seconds. At temperature tº, Engler viscosity is denoted by the symbol Et, and its unit is conditional degrees. 　　②Sagbolt viscosity, also known as Sagbolt viscosity. It is the number of seconds required for a certain amount of sample to flow 200 milliliters through a Saybolt viscometer at a specified temperature (such as 100ºF, 210ºF, or 122ºF, etc.), measured in seconds. Saybolt viscosity is further divided into Saybolt universal viscosity and Saybolt heavy oil viscosity (or Saybolt Furol viscosity). 　　③Ree’s viscosity is also known as Redwood viscosity. It is the number of seconds required for a certain amount of sample to flow 50 milliliters from a Reymond thermometer at a specified temperature, measured in seconds. Ree’s viscosity is further divided into Ree’s No. 1 (denoted as Rt) and Ree’s No. 2 (denoted as RAt). 　　The above three viscosity measurement methods are commonly used in European and American countries. In China, aside from the use of the Engler viscometer for measuring dark lubricants and residue oils, the other two types of viscometers are rarely utilized. The three methods for expressing conditional viscosity have different units, but their relationships can be converted using charts. At the same time, Engler viscosity and kinematic viscosity can also be converted to one another, which makes things much more convenient and flexible. The property of internal friction arising between fluids is known as the viscosity of those fluids. 　　Dynamic viscosity refers to the ratio of the internal friction force per unit area of contact in a fluid to the rate of change of velocity perpendicular to the direction of motion. 　　Kinematic viscosity is the ratio of dynamic viscosity to the density of the fluid at the same temperature and pressure.

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Reply to 2# wql815: Thank you very much