What is the viscosity, the viscosity index? The importance of viscosity

Viscosity is an important quantity that affects the motion of a fluid. The following article will help you better understand viscosity and its importance in production and life.

What is the viscosity?

The viscosity of the lubricant is the most important property. It can be defined as the oil’s resistance to flow and shear. Proactively monitoring lubricant viscosity can make a big difference to the health and life of your machinery.

Viscosity index

Every liquid has its own measurement, known as the viscosity index or viscosity parameter, represented by the Greek letter. The coefficient is proportional to the efficiency required to cut a fluid.

A viscous fluid requires a source of pressure to move. The difference in fluid velocity between the contact edge (where it is zero) and the center is another measure of viscosity. This velocity gradient is small for viscous liquids, which means that the velocity is not much greater at the center than it is in its direction.

The thicker the fluid, the smaller the strain or velocity than the thin thick fluid.

Influential factors

The viscosity coefficient is affected by temperature. The viscosity of a liquid will usually decrease as the temperature increases. In addition, this quantity is also affected by a number of factors such as contamination with water, particles or other lubricants.

Viscosity of some familiar fluids

Most common fluids have a viscosity index on the order of 1 to 1,000 mPa s, while for gases it will be between 1 and 10 μPa s.

Viscosity index of water

Actually water is not viscous, but in fact, using viscometers can accurately determine the viscosity index of water.</ span>

The viscosity index of water at 20 ℃ is 1.0020 millipascal seconds.

Blood viscosity index

Blood is composed of red blood cells, platelets and white blood cells that exist in plasma. Blood circulates continuously throughout the human body and the viscosity index of blood depends on many factors such as the viscosity of the plasma, the ratio of red blood cells, white blood cells to platelets or the degree of concentration of the blood.

The viscosity index of blood at 37 degrees Celsius is 23 – 4.1 Centipoise, denoted by the letter η. This is an approximation and may not be accurate for everyone.

What is the viscosity index of the oil?

Oil here is the lubricant used in the engines of motorcycles, cars or other motor vehicles. Viscosity helps to save fuel and generate horsepower for the engine. In addition, it is the factor that helps the car engine operate at the highest capacity. The viscosity coefficient of oil depends on the type of car engine with horsepower and speed, fast or slow.

Viscosity index of some familiar fluids:

Importance 

If plotted with viscosity on the vertical axis and temperature on the horizontal axis, the slope will be more horizontal with a higher viscosity coefficient.

Some oils may have the right viscosity index at certain temperatures but not quite meet the needs of both ends of the range. temperature. Remember that a small difference in temperature can equate to a large change in viscosity which can be detrimental to machinery.

For example, if the viscosity index is too high, it can lead to low oil flow, causing oil starvation and dry starts. When the viscosity index is too low, greater mechanical friction can occur, resulting in heavier loads. You will also see more wear due to film loss.

Additives can be used to improve the viscosity index. This allows lubricants to be formulated to meet equipment manufacturer specifications. You should check the equipment manufacturer’s specifications to determine the right lubricant, and consider climatic and operating conditions when selecting. With the correct installation and the correct viscosity index, you can be sure to achieve the maximum life and reliable operation of your machinery.

Viscosometry

There are many ways to help you determine the viscosity index from manual to using the most modern methods. Below, Hiep Phat will introduce some of the most popular ways:

Using capillary viscosity index meter

This is the first method for measuring the viscosity index that is based on the use of capillary tubes and measures the time it takes for an amount of liquid. across the length of the tube. This method has been used since the 20th century until now.

Zahn Cup Method

Contains 1 small viscometer cup with handle and a small hole in the bottom. The time to separate the cup through the hole correlates with the viscosity. Zahn cups are commonly used in the paint industry.

Measurement of falling bridge viscosity

Another technique is the falling-ball viscometer, where a sphere of known density is dropped into the liquid sample and the time it takes for the ball to fall to a specified point is recorded. This method has been used on board ships to monitor the quality of fuel entering the ship’s engines.

Vibration meter

Vibration viscometers measure the damping of an oscillating electric resonator immersed in a liquid. This technique is often used in the production of a product line, or in other process applications.

Rotary Viscometer

Rotating viscometer measures the torque required to turn an object in a fluid as a function of the fluid’s viscosity . This method is commonly used in production and quality control laboratories.

Hopefully, the above article has helped you better understand the concept of viscosity as well as the measurement method. effective viscosity index. If you are looking to buy genuine, high-quality viscometers, do not hesitate to contact Hiep Phat via Hotline: (028) 6287 4765 or Email : sales@thietbihiepphat.com to receive timely advice.