What is the shear rate in a plunger pump and how does it affect the fluid?

Hey there! As a plunger pump supplier, I often get asked about the shear rate in a plunger pump and how it affects the fluid. So, I thought I'd write this blog to break it down for you in simple terms.

First off, let's talk about what shear rate is. Shear rate is basically a measure of how fast one layer of fluid slides over an adjacent layer. In a plunger pump, this happens when the plunger moves back and forth, creating a force that causes the fluid to flow. The shear rate is determined by the speed of the plunger and the distance between the layers of fluid.

Now, you might be wondering why shear rate matters. Well, it can have a big impact on the fluid's properties and how it behaves in the pump. For example, high shear rates can cause the fluid to heat up, which can lead to a decrease in viscosity. This can be a problem if the fluid needs to maintain a certain viscosity to function properly. On the other hand, low shear rates might not provide enough force to move the fluid effectively through the pump.

Let's take a closer look at how shear rate affects different types of fluids.

Newtonian Fluids

Newtonian fluids are those whose viscosity remains constant regardless of the shear rate. Examples of Newtonian fluids include water and most simple oils. In a plunger pump, the shear rate will mainly affect the flow rate of these fluids. A higher shear rate will generally result in a higher flow rate, as the force from the plunger is more effectively transferred to the fluid. However, if the shear rate gets too high, it can cause cavitation, which is the formation of vapor bubbles in the fluid. Cavitation can damage the pump and reduce its efficiency.

Non - Newtonian Fluids

Non - Newtonian fluids are a bit more complex. Their viscosity changes with the shear rate. There are different types of non - Newtonian fluids, such as shear - thinning and shear - thickening fluids.

Shear - thinning fluids, also known as pseudoplastic fluids, decrease in viscosity as the shear rate increases. Many polymer solutions and some types of paints are shear - thinning. In a plunger pump, a higher shear rate can make these fluids easier to pump, as the reduced viscosity allows for smoother flow. This can be beneficial in applications where a high flow rate is required.

Shear - thickening fluids, or dilatant fluids, increase in viscosity as the shear rate increases. Some suspensions of solid particles in a liquid are shear - thickening. In a plunger pump, a high shear rate can make these fluids more difficult to pump, as the increased viscosity can cause blockages and reduce the pump's performance.

Now, let's talk about how we, as a plunger pump supplier, take shear rate into account when selecting and designing pumps.

When choosing a plunger pump for a specific application, we need to know the type of fluid that will be pumped. If it's a Newtonian fluid, we can focus more on the flow rate requirements and the potential for cavitation at high shear rates. For non - Newtonian fluids, we need to understand the fluid's shear - rate - viscosity relationship. We might adjust the pump's speed or the design of the pumping chamber to ensure that the shear rate is within an acceptable range for the fluid.

We also offer a variety of pumps that are suitable for different shear rate requirements. For example, the Rexroth Pump A4FO28/31R - PSC02K01 is a high - performance pump that can handle a wide range of shear rates. It's designed to provide a consistent flow of fluid, whether it's a Newtonian or non - Newtonian fluid.

Another great option is the A20VLO190DRS/10R - NZD24N00 Radial Hydraulic Pump. This pump is known for its ability to handle high - pressure applications and can be adjusted to control the shear rate according to the fluid's properties.

And for heavy - duty applications like in excavators, our Rexroth A7VO355 Piston Pump Excavator EX400 is a top choice. It can maintain a stable shear rate even when pumping thick or abrasive fluids.

In conclusion, understanding the shear rate in a plunger pump and how it affects the fluid is crucial for ensuring the proper operation of the pump and the quality of the fluid being pumped. Whether you're dealing with a simple Newtonian fluid or a complex non - Newtonian fluid, we have the expertise and the right pumps to meet your needs.

If you're in the market for a plunger pump and want to discuss your specific requirements, don't hesitate to reach out. We're here to help you find the best solution for your application.

References

1. "Fluid Mechanics" by Frank M. White
2. "Handbook of Non - Newtonian Fluid Mechanics" by Ronald G. Larson