Apparent Viscosity Vs Dynamic Viscosity

The Sticky Situation: Unraveling the Mystery of Apparent vs. Dynamic Viscosity

Ever wondered why honey pours so slowly compared to water, even though both are liquids? The answer lies deeper than just "thickness"—it’s all about viscosity. But there's a twist: the viscosity isn't always what it seems. We encounter two key types: dynamic viscosity (also known as absolute viscosity) and apparent viscosity. Understanding the difference is crucial, not just for satisfying our curiosity about honey, but for everything from designing pipelines to creating the perfect skincare lotion. Let's dive into the fascinating world of fluid flow and unravel this sticky situation.

1. Dynamic Viscosity: The True Measure of Resistance

Imagine pushing a flat plate through a liquid. The resistance you feel is a direct measure of the liquid's dynamic viscosity (μ). It represents the internal friction within the fluid itself – the resistance of adjacent layers of fluid to move past each other. Think of it as the inherent stickiness of the fluid at a given temperature and pressure. Dynamic viscosity is a fundamental property, measured in Pascal-seconds (Pa·s) or centipoise (cP). Water, with its low internal friction, has a low dynamic viscosity. Molasses, with its high internal resistance, has a much higher dynamic viscosity.

Real-world example: Engine oil's dynamic viscosity is crucial. A low viscosity oil flows easily at low temperatures, ensuring quick engine lubrication during cold starts. However, too low a viscosity means insufficient lubrication at high temperatures and operating speeds, leading to engine wear. Conversely, too high a viscosity hinders efficient engine operation.

2. Apparent Viscosity: A Trick of the Eye (and the Shear Rate)

Now, things get interesting. While dynamic viscosity reflects the inherent resistance of a fluid, apparent viscosity (η) is a measure of the viscosity under specific flow conditions. The key difference lies in the shear rate, which describes how quickly the fluid is being deformed. Many fluids, especially non-Newtonian fluids, don't behave consistently across different shear rates.

Think of ketchup: it resists flow from the bottle (low shear rate), giving the impression of high viscosity. But once you start stirring vigorously (high shear rate), it flows much more readily, exhibiting a lower apparent viscosity. This is because the internal structure of ketchup changes under shear stress. Apparent viscosity is also measured in Pa·s or cP, but it's crucial to remember its context-dependent nature.

Real-world example: Polymer solutions used in 3D printing often display shear-thinning behavior. At low shear rates (during dispensing), they have a high apparent viscosity to maintain their shape. However, at high shear rates (during nozzle extrusion), their apparent viscosity decreases, allowing for smooth flow and precise deposition.

3. The Newtonian vs. Non-Newtonian Divide

The distinction between dynamic and apparent viscosity is especially important when dealing with non-Newtonian fluids. Newtonian fluids, like water and many oils, have a constant dynamic viscosity that is independent of the shear rate. Their apparent viscosity equals their dynamic viscosity.

Non-Newtonian fluids, on the other hand, exhibit shear-thinning (pseudoplastic), shear-thickening (dilatant), or thixotropic behavior. Their apparent viscosity changes with the shear rate. Ketchup, blood, and many polymer solutions are classic examples of non-Newtonian fluids.

Real-world example: Blood, a non-Newtonian fluid, behaves differently in large and small blood vessels. In larger vessels, the shear rate is high, and blood exhibits a lower apparent viscosity, ensuring efficient flow. In smaller vessels, the shear rate is lower, leading to a higher apparent viscosity. This adaptability is crucial for efficient blood circulation throughout the body.

4. Measurement Techniques: Seeing the Viscosity

Measuring dynamic viscosity often involves techniques like capillary viscometry or rotational rheometry. For apparent viscosity, rotational rheometers are more commonly used, as they allow for controlled variation of the shear rate, providing a complete viscosity profile.

Real-world example: Quality control in the food industry relies heavily on viscosity measurements. Determining the apparent viscosity of yogurt at different shear rates ensures consistent texture and flow properties across batches. Similarly, measuring the dynamic viscosity of chocolate helps maintain the desired fluidity for processing and consumer experience.

Conclusion: A Clearer Picture

While dynamic viscosity provides a fundamental measure of a fluid's internal resistance, apparent viscosity offers a more practical perspective, considering the influence of shear rate. Understanding the difference, particularly in the context of Newtonian versus non-Newtonian fluids, is vital for a wide range of applications – from designing efficient industrial processes to developing innovative consumer products. This distinction isn't just an academic exercise; it's the key to understanding the behavior of fluids in the real world.

Expert FAQs:

1. Can a fluid have a negative apparent viscosity? No. Viscosity represents resistance to flow; negative viscosity would imply a fluid flows with the application of no force or even accelerates backward, which is physically impossible.

2. How does temperature affect apparent and dynamic viscosity? Both are typically temperature-dependent. Increased temperature usually lowers viscosity for liquids, as increased molecular kinetic energy reduces intermolecular forces. However, the relationship can be complex and material-specific.

3. What are some advanced techniques for measuring viscosity in complex fluids? Advanced techniques include oscillatory rheometry (for studying viscoelasticity), microfluidic rheometry (for small sample volumes), and nuclear magnetic resonance (NMR) techniques.

4. How does pressure influence viscosity? The effect of pressure on viscosity is generally small for liquids, but can be significant for gases. Increased pressure generally increases the viscosity of liquids and gases.

5. Can we use apparent viscosity to predict dynamic viscosity? Only for Newtonian fluids, where they are equal. For non-Newtonian fluids, you would need to measure the apparent viscosity at multiple shear rates and potentially model the data to extract information about the underlying dynamic viscosity. A single apparent viscosity measurement at one shear rate does not fully define the fluid’s viscosity.

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What are the Differences between Dynamic and Kinematic 26 Sep 2015 · Simply put, dynamic viscosity gives you information on the force needed to make the fluid flow at a certain rate, while kinematic viscosity tells how fast the fluid is moving when …

What is Viscosity? | Computational Fluid Dynamics | SimScale 11 Aug 2023 · The most commonly used in the field of fluid dynamics is the shear — or dynamic viscosity — represented here as μ. However, depending on the flow physics, different viscosities play corresponding important roles.

Apparent Viscosity - an overview | ScienceDirect Topics The apparent viscosity of a fluid is the viscosity that fluid appears to have on a given instrument at a stated rate of shear. Apparent viscosity is another expression of effective viscosity (Huang et …

3.8: The Relative or Apparent Viscosity - Engineering LibreTexts Einstein (1905) published an analysis for the viscosity of dilute suspensions. The result of this analysis is an equation giving the relation between the apparent dynamic viscosity and the volumetric concentration of the solids. The concentrations however …

2.2: Viscosity Theory - Chemistry LibreTexts Viscosity is the result of frictional interactions within a given liquid and is commonly expressed in two different ways. The first is dynamic viscosity, also known as absolute viscosity, which measures a fluid’s resistance to flow.

Basics of viscometry | Anton Paar Wiki The kinematic viscosity v (ny) is the dynamic viscosity divided by density ρ ( rho) when both parameters of the material are taken at the same temperature and pressure.

Types of Viscosity (Dynamic, Kinematic, Apparent) in context of … 10 Aug 2024 · In this article, we will delve into the concepts of dynamic, kinematic, and apparent viscosity, exploring their definitions, formulas, and practical implications.

Different viscosities (fluid mechanics, rheology, polymer physics ... Apparent viscosity refers to the viscosity instant, i.e. the viscosity value at time t as measured in a device intended for this purpose. This notion takes into account the fact that for most products, the viscosity measured depends on the shear stresses applied to it.

012_ViscosityAndViscousForces_LectureNotes - Purdue University The apparent viscosity, μapp, is the viscosity at the local conditions as shown in the plot below (for a Newtonian fluid the apparent viscosity remains constant).

Apparent viscosity - Wikipedia The apparent viscosity of a fluid depends on the shear rate at which it is measured. The apparent viscosity of a dilatant fluid is higher when measured at a higher shear rate (η4 is higher than η3), while the apparent viscosity of a Bingham plastic is lower (η2 is lower than η1).

Viscosity - Absolute (Dynamic) vs. Kinematic - The Engineering ToolBox Vicosity is a fluid's resistance to flow and can be valued as dynamic (absolute) or kinematic. Viscosity is an important fluid property when analyzing liquid behavior and fluid motion near solid boundaries. The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress.

General Chapters: <911> VISCOSITY - uspbpep.com Many substances, such as the gums employed in pharmacy, have variable viscosity, and most of them are less resistant to flow at higher flow rates. In such cases, a given set of conditions is selected for measurement, and the measurement obtained is considered to …

NotesOnThermodynamicsFluidMechanicsAndGasDynamics_Was… In shear thickening (aka dilatant) fluids, the apparent viscosity increases as the shear stress increases. An example of a shear thickening fluid is quicksand or a thick cornstarch-water mixture.

Notes on Thermodynamics, Fluid Mechanics, and Gas Dynamics 6 Sep 2023 · pparent viscosity increases as the shear stress increases. An example of a shear thickening fluid is q ly dependent on pressure, but is sensitive to temperature. For liquids, the viscosity generally decreases as the

So many different types of viscosity! Why and what do they Why are there different viscosities? 1 st – various types of deformation • Viscosity versus concentration or volume fraction • Dilute • Semi-dilute • Full range • Scaled viscosity parameters • Relative – 𝜂𝜂

What is the Difference Between Dynamic and Kinematic Viscosity? Dynamic Viscosity: viscosity related to the external force applied to non-Newtonian fluids. Kinematic Viscosity: inherent viscosity of Newtonian fluids, that does not change with a change in applied force.

Learn about Viscosity and Viscometry | AMETEK Brookfield This measured viscosity is called the apparent viscosity of the fluid and is accurate only when explicit experimental parameters are furnished and adhered to. Non-Newtonian flow can be envisioned by thinking of any fluid as a mixture of molecules with different shapes and sizes.

Types of Viscosity & When to Apply Them - RheoSense 30 Mar 2021 · Steady shear (apparent) viscosity – refers to the relationship between viscosity and shear rate, more specifically the shear stress applied to a fluid divided by the shear rate. So, we have the different viscosities defined, but what does it all really mean?

Microsoft Word - Viscosity Definitions.doc - University of Utah In the case of non-Newtonian fluids, the ratio varies with the shearing stress, and viscosities of such fluids are called apparent viscosities. In the new SI system, it is proposed that values for the Poise be stated as Pascal seconds, the conversion factor being 1 Poise equal to 1 × 10-1 Pa·s.

Chapter 5: Viscosity - Engineering LibreTexts Intrinsic Viscosity Measurements Clearly viscosity and molecular weight are critical parameters and we can measure intrinsic viscosity which will then reveal other important polymer properties like solvent conditions and viscosity-average molecular weight.

A comparison between apparent viscosity and dynamic complex viscosity ... 1 Jan 1997 · To observe further relationships and differences between the two viscosity terms, we present this paper, in which we report apparent shear and dynamic complex viscosity data at 200 [degrees] C and 230 [degrees] C for both homopolypropylene (PPVC)/ maleic anhydride grafted polypropylene (PP-g-MA) and ethylene-propylene copolymer (PPSC)/PP-g-MA ...

Apparent Viscosity Vs Dynamic Viscosity

The Sticky Situation: Unraveling the Mystery of Apparent vs. Dynamic Viscosity

1. Dynamic Viscosity: The True Measure of Resistance

2. Apparent Viscosity: A Trick of the Eye (and the Shear Rate)

3. The Newtonian vs. Non-Newtonian Divide

4. Measurement Techniques: Seeing the Viscosity

Conclusion: A Clearer Picture

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