Advantages and disadvantages of drum method and falling ball method for measuring liquid viscosity

The advantages and disadvantages of drum method and falling ball method for measuring liquid viscosity are as follows:

1 Drum method: it has a wide measuring range, and is suitable for laboratory sampling measurement, and can be used for viscosity measurement of high-viscosity samples at low shear rate. Disadvantages: the measurement results are greatly influenced by the properties of the fluid, such as the density, viscosity and conductivity of the fluid.

2. Advantages of the falling ball method: it is suitable for laboratory sampling measurement and has a wide range, especially for viscosity measurement of high-viscosity samples at low shear rate. Disadvantages: the measurement results are greatly influenced by the size, shape and density of the sphere.

In China, except Engel viscometer, the other two viscometers are rarely used. The expression methods and units of the three conditional viscosities are different, but the relationship between them can be converted by charts. At the same time, Engler viscosity and kinematic viscosity can also be converted, which is much more convenient and flexible.

There are many methods to measure viscosity, such as rotating barrel method, falling ball method, damping vibration method, cup viscometer method, capillary method and so on. Suitable for low viscosity fluids, such as water, ethanol, carbon tetrachloride, etc. , capillary viscometer is often used to measure; But it is transparent (or translucent) for high viscosity fluids, such as castor oil, transformer oil, engine oil and glycerol.

Common drop ball method; For liquids with viscosity ranging from 0. 1 to100 pa s, the drum method can also be used for determination. The principle of measuring viscosity in laboratory is generally to derive the expression of viscosity coefficient from Stokes formula and Marie Poi formula, and get the viscosity coefficient.

Viscosity depends on the nature and temperature of the liquid. With the increase of temperature, the viscosity will decrease rapidly. Therefore, it is meaningful to measure viscosity and accurately control the temperature change. The determination of viscosity parameters has important guiding value for predicting the process control, transportation and operability of products in the production process, and is of great significance in printing, medicine, petroleum, automobile and many other industries.

1845, British mathematician and physicist G.G. Stokes (18 19- 1903) and French C.L.M.H Naville respectively deduced the most basic equations in viscous fluid mechanics.

185 1 year, Stokes deduced the formula for calculating the resistance of a solid sphere moving slowly in a viscous medium, and obtained that the resistance is proportional to the velocity and viscosity coefficient under a given force (gravity), that is, the Stokes formula for resistance.

Navier-Stokes equation is one of the most difficult nonlinear equations in mathematics, and it is difficult to find its exact solution. There are only about 70 exact solutions and only about 100 special solutions, which is one of the most complicated and unsolved world-class mathematical problems.