# Pumps for highly viscous media

Viscosity indicates the flow properties of various media.

Die viscosity is a property of fluids that characterizes their flow properties. It indicates how easily or heavily a fluid flows. Fluids with high viscosity flow more slowly and are thicker, while fluids with low viscosity flow faster and are less viscous.

## What is viscosity?

To make viscosity easier to understand, it helps to take a closer look at honey and water side by side on an inclined plane. Water is low viscosityHoney, on the other hand, has a high viscosity on. As a result, honey flows significantly more slowly along the inclined plane. Honey has a high flow resistance and water has a low flow resistance. This flow resistance is also known as viscosity in technical language. Viscous media, to which liquids But gases can also be included, are referred to as fluids.

## How does viscosity arise?

In the interior of liquids and Gasen Are there particles. The viscosity depends on the behavior of the particles inside the substance. Within a substance with a high viscosity, there are strong forces of attraction between the particles. The particles inside are always moving and they are constantly bumping into each other and hindering each other.

In the case of media with low viscosity, these forces of attraction are rather low. For media higher viscosityt, is this gravitational pull of the particles higher, so that the substance or the liquid is less mobile. This state is referred to as internal friction. This internal friction results from molecular forces and, in addition, from the exchange of momentum between the particles. Internal friction can be easily represented by interlocking molecular layers. To release this interlocking, force is required. The magnitude of the force applied depends on the strength of the viscosity.

Thermal energy, for example, can be seen as the effect of force. When a substance is heated, its viscosity changes.

## How do you measure viscosity?

Viscosity is generally not particularly easy to calculate. However, it is measured with a viscometer. The viscometer forces the medium to move and the resulting resistance is measured.

## How is viscosity stated?

At the dynamic viscosity Will the flow resistance within the liquid specified. In laboratory reports, for example, the viscosity is given in mPas (milli-pascal-seconds) or, more rarely, in cP (centi-poise). In the case of a calculation, the SI unit is equal to kg/m per s.

To simplify this calculation, it can be represented using two plates arranged in parallel. plate A and plate B, in this example, include a film of liquid between them. Plate A always moves parallel to base plate B at a constant speed. This linear movement results from a Force action F . The liquid layer directly below plate A adheres to it and moves in the respective direction of movement. However, the shift decreases the further away the liquid layer is from plate A. The liquid layer, which is directly on plate B, remains motionless just like plate B.

This means that dynamic viscosity equals shear stress (force F divided by moving plate A) divided by shear rate (speed divided by liquid film thickness).

## What is kinematic viscosity?

A distinction is made between kinematic and dynamic viscosities. Dynamic viscosity measures the toughness of the substance, which depends on the substance. It is expressed in pascal seconds.

The kinematic viscosity, on the other hand, helps to compare two different substances, defined by the Viscose-density ratio.

The measurement and presentation of dynamic viscosity has been described as demanding task proven. The determination of kinematic viscosity has therefore proved to be much more practical. The defined viscose-density ratio is shown in the SI unit mm² per s and in very rare cases as in “centistoke” (cSt).

It is measured based on the duration of a particular amount of liquid needed at a certain temperature to travel a distance. Gravity helps with this and high precisionto find out the kinematic viscosity. With the help of flow rate and the capillary constant of the “viscometer” is then calculated.

If you now divide the dynamic viscosity by the density, you get the kinematic viscosity. If you multiply this kinematic viscosity by the density, you get the dynamic viscosity again.

## Can the viscosity change?

The viscosity of so-called Newtonian liquids does not change. They maintain their viscosity even when energies act on them. This results from the, set up by Isaac Newton flow laws the mechanics. water, oil And alcohol is Newtonian liquids and therefore do not change their viscosity.

As a result, non-Newtonian fluids occasionally change their viscosity. Non-Newtonian liquids include ketchup, blood or even water-starch mixtures.

Using the example of the water-starch mixture, non-Newtonian liquids Explain very well. If you mix water and starch together in a ratio of 1:2 and then hit the fist quickly and with a little more pressure, you can feel resistance.

## How does the change in viscosity occur when exposed to thermal energy?

When butter is heated, the viscosity changes from originally 1.5 mPa·s at 5° C. to 1.0 mPa·s at 20° C. This means that viscosity has been reduced by a third.

But how does this come about?

Heat expands the distances between the atoms inside the substance. This is because if there are more internal distances, the intermolecular forces of attraction are reduced, meaning that the interconnections become less.

## Which pumps are particularly suitable for highly viscous media or viscous liquids?

Viscous liquids are very demanding. Pumps for viscous substances must highest reliability show. The first obstacle occurs even before the medium even gets inside the pump. It must be ensured that the substance can flow to the inlet opening. Once this hurdle has been overcome, it is time to overcome the next one. The viscose fabric or even the solid-containing liquid must not cause any problems with the pump. Liquids containing solids can also smallest quantities included in pieces.

Die optimal solution Displacement pumps are suitable for this - in addition to the compressed air diaphragm pump, the wobble ring pump as manufactured by pumpsystems is particularly suitable. Through the careful conveyance of highly viscous liquids Has this type of pump many advantages over conventional pumps.

Compressed air diaphragm pumps, also known as double diaphragm pumps, consist of two liquid chambers, two air chambers and two membranes. One membrane sucks in the liquid and the other membrane transports the Medium back to the outside world.

Find out more about diaphragm pumps over here

Rotating ones are also suitable positive displacement pumps. Even with high Differences in pressure They enable linearly controlled product delivery and therefore also reliable Dosing result.

Examples of rotating positive displacement pumps are screw pumps, eccentric screw pumps or even gear pumps.

The most popular rotary positive displacement pump is the piston pump.

Die piston pump Can you imagine yourself in a T-shape. Inside, there is a piston which moves up and down. The inlet and outlet are located on the side. If you now operate the pump, the piston moves downwards. As a result of the fact that the liquid to be pumped is in a container above the pump, a vacuum is now created in it. As a result, the intake and exhaust valve alternately close and open. When the piston returns to the top, the medium flows out of the pump.

Here You can find out more about viscosity.

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