How to calculate the viscous force

1.

τ= η dv/dx = η D (Newton formula) where η It is related to the material properties

The kinematic viscosity is the dynamic viscosity of the fluid and the density of the fluid at the same temperature ρ The ratio of the two. The unit is (m ^ 2) / s. It is represented by the small letter v. Note: the unit used in the past is st (s), and the relationship between ST (s) and (m ^ 2) / S is: 1 (m ^ 2) / S = 10 ^ 4st = 10 ^ 6cst Among them, "CST" is read as "LISS") regards the flowing liquid as many liquid layers moving in parallel with each other, and each layer has different velocity, forming a velocity gradient (DV / DX), which is the basic characteristic of flow

There are three methods to measure dynamic viscosity, kinematic viscosity and conditional viscosity

(1) dynamic viscosity η T is the resistance proced when the two liquid layers are 1 cm apart, each with an area of 1 (square centimeter) and a relative moving speed of 1 cm / s, in grams per meter per second. 1 g / cm · s = 1 poise general: the unit of dynamic viscosity in instry is expressed in poise

(2) kinematic viscosity: when the temperature is t ℃, the kinematic viscosity is expressed by symbol γ Indicates that in the international system of units, the unit of kinematic viscosity is s, i.e. square meters per second (m2 / s), which is commonly used in actual measurement, and (CST) indicates that the unit of centigrade is square millimeter per second (i.e. 1cst = 1mm2 / s)

The kinematic viscosity is widely used to measure the viscosity of jet fuel oil, diesel oil, lubricating oil and other liquid petroleum procts, dark petroleum procts, used lubricating oil, crude oil, etc

(3) conditional viscosity: refers to the viscosity in conditional units measured by different specific viscometers

2. Some viscosity of hydraulic oil is that the flowing hydraulic oil is regarded as many liquid layers moving parallel to each other, and the velocity of each layer is different, forming a velocity gradient (DV / DX), which is the basic characteristic of flow.
e to the existence of velocity gradient, the slow flowing liquid layer blocks the flow of the faster liquid layer, so the liquid has resistance to movement, A reverse force opposite to the resistance must be applied to the liquid layer.
the force applied on the unit liquid layer area is called shear stress τ( Shear rate (d) d = d v / D x (s-1)
shear stress and shear rate are two basic parameters characterizing the rheological properties of the system.
two parallel fluids with different planes have the same area "a" and distance "DX", and flow in the same direction with different flow rates "V1" and "V2", Newton assumed that the force to maintain the different velocity is proportional to the relative velocity or velocity gradient of the fluid, that is:
τ= η dv/dx = η D (Newton formula) where η It is related to the properties of the material, we call it "viscosity"
definition of viscosity: two plates with an area of 1m2 are immersed in liquid, and the distance between the two plates is 1m. If the relative velocity between the two plates is 1mgs by adding 1n shear stress, the viscosity of the liquid is 1pA. S
Newtonian fluid: a fluid conforming to Newton's formula. Viscosity is only related to temperature, but not to shear rate, τ It is proportional to d
non Newtonian fluid: does not conform to Newton formula τ/ D = f (d), with η A means definitely τ/ D) The apparent viscosity is defined as the viscosity at the same temperature
there are three methods for viscosity measurement: dynamic viscosity, kinematic viscosity and conditional viscosity
(1) dynamic viscosity: η T is the resistance proced when the two liquid layers are 1 cm apart, each with an area of 1 (square centimeter) and a relative moving speed of 1 cm / s, in grams per meter per second. 1 g / cm · s = 1 poise general: the unit of dynamic viscosity in instry is expressed in poise
(2) kinematic viscosity: when the temperature is t ℃, the symbol for kinematic viscosity is used γ Indicates that in the international system of units, the unit of kinematic viscosity is s, i.e. square meters per second (m2 / s), which is commonly used in actual measurement, and (CST) indicates that the unit of centigrade is square millimeter per second (i.e. 1cst = 1mm2 / s). Kinematic viscosity is widely used to determine the viscosity of jet fuel oil, diesel oil, lubricating oil and other liquid petroleum procts, dark petroleum procts, used lubricating oil, crude oil, etc. the measurement of kinematic viscosity adopts countercurrent method
(3) conditional viscosity: refers to the viscosity in conditional units measured by different specific viscometers, There are three kinds of conditional viscosity commonly used in various countries:
① Engler viscosity is also called Engler viscosity. It is the ratio of the time required for a certain amount of sample to flow out 200 ml of sample from Engler viscometer at the specified temperature (such as 50 ℃, 80 ℃, 100 ℃) and the time (seconds) required for distilled water to flow out the same volume at 20 ℃. Temperature T & ordm; The unit of Engler viscosity is conditional degree< (2) sagbolt viscosity. Is a certain amount of sample, at a specified temperature (such as 100 & ordm; F、F210º F or 122 & ordm; The number of seconds required to flow 200 ml from the Saybolt viscometer in seconds. Saybolt Viscosity is divided into Saybolt general viscosity and Saybolt heavy oil viscosity (or furol viscosity)< (3) Redwood viscosity. Is the number of seconds, in seconds, required for a certain amount of sample to flow 50 ml from the Ralston's meter at the specified temperature. Reynold viscosity is divided into Reynold 1 (RT) and Reynold 2 (rat)
the above three kinds of conditional viscosity determination methods are commonly used in European and American countries. In China, the other two kinds of viscosimeters are rarely used except the Engler viscometer for the determination of dark lubricating oil and resial oil. The three kinds of conditional viscosities are expressed in different ways and units, but their relationship can be converted by chart. At the same time, Engler viscosity and kinematic viscosity can also be converted, which is much more convenient and flexible< There are many methods for viscosity determination, such as rotating barrel method, falling ball method, damping vibration method, cup viscometer method, capillary method and so on. For fluids with low viscosity, such as water, ethanol, carbon tetrachloride and so on, capillary viscometer is commonly used to measure; For the more viscous fluids, such as castor oil, transformer oil, engine oil, glycerin and other transparent (or translucent) liquids, drop ball method is commonly used; For the viscosity of 0.1 ~ 100Pa and 8226; The liquid in the range of S can also be determined by rotating cylinder method
the principle of viscosity measurement in laboratory is to derive the expression of viscosity coefficient from Stokes formula and Poiseuille formula to obtain the viscosity coefficient
the viscosity depends on the properties and temperature of the liquid. With the increase of temperature, the viscosity will decrease rapidly. Therefore, in order to measure the viscosity, it is necessary to control the change of temperature accurately. The determination of viscosity parameters has important guiding value for predicting the process control, transportability and operability of procts in the proction process
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3.

τ Dynamic viscosity= η dv/dx = η D (Newton formula) where η It is related to the material properties

The kinematic viscosity is the dynamic viscosity of the fluid and the density of the fluid at the same temperature ρ The ratio of the two. The unit is (m ^ 2) / s. It is represented by the small letter v

Newtonian fluid: a fluid conforming to Newton's formula. Viscosity is only related to temperature, but not to shear rate, τ It is proportional to d

non Newtonian fluid: does not conform to Newton formula τ/ D = f (d), with η A means definitely τ/ D) The apparent viscosity is defined as the viscosity at the same temperature

extended data

there are three kinds of conditional viscosities commonly used in various countries

① Engler viscosity is also called Engler viscosity. It is the ratio of the time required for a certain amount of sample to flow out 200 ml of sample from Engler viscometer at the specified temperature (such as 50 ℃, 80 ℃, 100 ℃) and the time (seconds) required for distilled water to flow out the same volume at 20 ℃. Temperature T & amp; ordm; The unit of Engler viscosity is conditional degree

(2) sagbolt viscosity. Is a certain amount of sample, at a specified temperature (e.g. 100 & amp; ordm; F、F210& ordm F or 122 & amp; ordm; The number of seconds required to flow 200 ml from the Saybolt viscometer at & quot; Second & quot; Company. Saybolt Viscosity is divided into Saybolt general viscosity and Saybolt heavy oil viscosity (or furol viscosity)

(3) Redwood viscosity. Is the number of seconds required for a certain amount of sample to flow 50 ml from the Ralston's meter at the specified temperature, expressed as & quot; Second & quot; Unit. Reynold viscosity is divided into Reynold 1 (RT) and Reynold 2 (rat)

4. This is what I found in gravity concentration for your reference.
Stokes formula is used for viscous resistance:
rs = 3 πμ DV (this is your formula expression, d = 2R carried in.)
or rs = (3 π/ Re) d^2 ρ V ^ 2
where d-particle diameter m
RS -- viscous resistance of medium to ore particles, N< br /> μ—— Dynamic viscosity of medium, or viscosity, PA · s< br /> ν—— The relative velocity of ore particles, M / s.
generally, the settlement of powdery materials (cement, clay powder, pulverized coal, etc.) and droplets in air or in pneumatic transportation is calculated according to Stokes formula. The settlement of fine solids (d < 0.1 mm) in water can also be calculated according to the above formula

5. If you can understand the resistance that people encounter when walking at different wind speeds, you will understand what viscous resistance is. Air has viscosity, and "wind" is the flow of air under pressure difference. The resistance that people feel in the air is related to wind speed, temperature and other factors
the viscous resistance of this liquid is also like this. Because there are many factors involved, the coefficient can only be obtained through experiments
it's quite popular. I hope you can understand.

6.

Kinematic viscosity ν=μ/ρ

μ Is the dynamic viscosity of liquid

0 ρ It is the density of liquid

and the dynamic viscosity of liquid μ=τ/(/ dy)

τ It is the internal friction resistance per unit area of liquid flow

/ dy is the velocity gradient

extended data:

the viscosity is the proportional constant, that is, the viscosity coefficient, which is equal to the tangential force value of the fluid per unit area when the velocity gradient is one unit. In the usual centimeter gram second system, the unit of viscosity coefficient is poise; In the international system of units, the unit of viscosity is pa · s

Newton's law of internal friction points out that when the fluid flow is laminar, the internal friction f between layers is directly proportional to the directional velocity gradient / DZ and laminar slice area a, respectively=- η*/ dz*A The proportion coefficient η It is the viscosity coefficient

η 1 poise (P) = 0.1kg / (m * s)

kinematic viscosity coefficient is a physical quantity used to measure the viscosity of fluid, which is the dynamic viscosity coefficient of fluid μ Its density ρ The ratio of the two. With symbols γ I.e γ=μ/ρ， The unit is m2 / s, γ It has no special physical meaning, because it has kinematic dimension, so it is called kinematic viscosity coefficient. The physical quantity it represents is the ratio of viscous force to inertial force. γ The value of depends on the properties, temperature and pressure of the fluid

7. Hydrodynamic viscosity coefficient is the inherent property of fluid, which is not calculated, but measured by experiment.

8. Everything has a viscous force

9. There is a formula that can show the relationship between the two units as follows:
1pA. S = 1kcps
Pa.s is Pascal. "Second" means
CP means "Li Po" and "K" means nothing to me

Pa.s = Pascal second
CPS = centipoise sec

both units belong to dynamic viscosity unit

centipoise is the unit of viscosity, for example:
the viscosity of water is 1 centipoise, so it is very easy to flow
molasses has a viscosity of 100000 centipoise, which is very thick