Viscosity & Rheology

Impact of Temperature and Shear Rate on Viscosity

When measuring viscosity, two key external factors—temperature and shear rate—can have a significant impact on the accuracy and reliability of the results. Understanding how these factors influence viscosity is crucial for ensuring product quality and optimizing processes across a wide range of industries, including motor oils, greases, adhesives, and other materials that are sensitive to changes in environmental conditions.

The Effect of Temperature on Viscosity

Temperature is one of the most influential factors on viscosity. In most fluids, viscosity decreases as temperature increases. This happens because higher temperatures give fluid molecules more energy, allowing them to move more freely and reducing the internal friction that causes viscosity. Conversely, as temperature decreases, fluid molecules move more slowly, and the viscosity increases.

For example:

Motor oils: At low temperatures, motor oils become more viscous (thicker), which can lead to sluggish flow and reduce engine efficiency. Conversely, at high temperatures, they become less viscous (thinner), potentially compromising their ability to lubricate.
Adhesives: Many adhesives become less viscous when heated, allowing for easier application, but if the temperature is too high, the adhesive may not perform as expected once it cools.
Greases: Industrial greases are often formulated to perform within specific temperature ranges. If the grease becomes too viscous at low temperatures, it may not flow properly, leading to equipment wear. If it becomes too thin at high temperatures, it may lose its ability to protect surfaces.

In practical applications, understanding how a material’s viscosity changes with temperature helps manufacturers optimize product formulations for specific operating conditions. Instruments like Brookfield’s viscometers and rheometers come equipped with temperature control features to ensure that accurate and consistent measurements are made, even under varying thermal conditions.

The Effect of Shear Rate on Viscosity

The shear rate refers to the rate at which adjacent layers of fluid move relative to each other. It is a critical factor when working with non-Newtonian fluids—those whose viscosity changes depending on the shear rate applied.

Newtonian fluids: In Newtonian fluids like water or mineral oils, viscosity remains constant regardless of the shear rate.
Non-Newtonian fluids: In many industrial applications, fluids exhibit non-Newtonian behavior, meaning their viscosity changes as the shear rate increases or decreases. There are two main types of non-Newtonian behavior:

Shear-thinning (pseudoplastic): Fluids like ketchup or certain paints become less viscous when shear is applied (e.g., when they are stirred or squeezed). This behavior is advantageous for processes where easy flow is needed under force, but stability is required when the force is removed.
Shear-thickening (dilatant): Fluids like cornstarch and water mixtures behave oppositely, becoming more viscous under higher shear rates. This can be challenging in processes where too much force can lead to increased resistance to flow.

Why Understanding Temperature and Shear Rate Matters

In many industries, materials are processed under varying conditions of temperature and shear. To maintain consistent product quality and ensure efficiency in production, it is essential to account for how these factors affect viscosity:

Motor oils must perform under both low and high shear rates, from the gentle flow in storage tanks to the intense shearing in an engine.
Greases and lubricants need to maintain a balance between flow and protection at varying temperatures and shear rates to prevent equipment failure.
Adhesives must flow easily for application but hold firm once applied, requiring an understanding of how shear and temperature affect their performance.

Neglecting these factors can lead to issues such as improper flow, inadequate mixing, or poor product performance, all of which can negatively impact efficiency and quality.

How AMETEK Brookfield Instruments Help Control for Temperature and Shear Rate

At Brookfield, we understand the importance of measuring viscosity accurately under real-world conditions. Our instruments are designed with precision temperature control and a range of spindle and speed options, enabling users to simulate different shear rates during testing. These features allow for the precise analysis of how fluids respond to both temperature and shear rate changes, ensuring that your products perform consistently across a wide range of operating conditions.

With our advanced viscometers and rheometers, you can fine-tune your measurements to replicate the exact environmental conditions in which your products will be used. This leads to more accurate data and helps you make better-informed decisions during product development and quality control.

Both temperature and shear rate significantly influence viscosity measurements, and understanding their effects is crucial for ensuring reliable results and optimal product performance. Whether you’re working with motor oils, greases, adhesives, or other complex fluids, accounting for these factors is essential for successful manufacturing and processing.

Brookfield offers the tools and expertise you need to measure viscosity under a variety of conditions, helping you maintain the highest standards of quality and efficiency. Our instruments provide accurate, real-world insights into how temperature and shear rate affect your materials, giving you the confidence to optimize your processes and deliver superior products.