Sofia Martinez
Plastic viscosity is a non-Newtonian property of fluids that describes the resistance of a fluid to flow. It is one of two types of viscosity, the other being apparent viscosity. Plastic viscosity is important in industrial and chemical applications, particularly when handling thick fluids, as it affects the flow properties of the fluid and has a significant impact on pump selection and performance. It is also a critical parameter in Bingham's plasticity model, where it indicates the viscosity of drilling mud at infinite shear rates. Understanding and controlling plastic viscosity in liquid transfer systems is essential for efficient and reliable operation, as it determines the power requirements and pump efficiency.
| Characteristics | Values |
|---|---|
| Definition | Plastic viscosity is a non-Newtonian property of a fluid and refers to the fact that a fluid does not flow until a shear force is applied. |
| Viscosity | Plastic viscosity is a measure of the viscosity of a fluid, including high-shear-rate viscosity. |
| Measurement | Plastic viscosity can be measured in a laboratory using a viscometer or in the field using a Marsh funnel. |
| Rheological Property | Plastic viscosity is a rheological property that depends on water content, aggregate properties, gradation of aggregates, mixing time, mixing system, and temperature. |
| Resistance | Plastic viscosity is the resistance of a fluid to flow, with high plastic viscosity resulting in increased pump pressures and decreased rate of penetration. |
| Pump Efficiency | Highly plastic viscous fluids require more force to overcome the initial resistance, which may affect pump efficiency and power requirements. |
| Temperature Control | Increasing the temperature of a plastic fluid decreases its viscosity, while lowering the temperature increases its viscosity. |
| Additives | The use of specially designed additives, such as modifiers and rheologists, can adjust the plastic viscosity of a fluid by changing its rheological properties. |
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What You'll Learn
Plastic viscosity is a non-Newtonian property of fluids
Newton's Law of Viscosity, named after Sir Isaac Newton, describes the flow behaviour of fluids with a simple linear relation between shear stress and shear rate. However, non-Newtonian fluids do not follow this law and exhibit variable viscosity dependent on stress and shear rate. For example, ketchup, a non-Newtonian fluid, becomes runnier when shaken.
Plastic viscosity is often used to describe very thick substances like slurries, paints, and other similar fluids that can retain their shape after the application of force is stopped. It is an important parameter in Bingham's plasticity model, along with the yield stress. The yield point is the maximum shear force at which a plastic fluid can retain its shape without flowing. Once the fluid begins to flow, the shear stress and shear rate are linearly related, and plastic viscosity measures the fluid's resistance to flow.
Understanding plastic viscosity is crucial for handling thick fluids in industrial and chemical applications. It impacts pump selection and performance, as highly plastic viscous fluids require more force to initiate flow, which can affect pump efficiency. Additionally, plastic viscosity influences liquid transfer and conveying system design, requiring pipe sizes to be large enough to accommodate the flow of highly plastic viscous liquids.
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It is a measure of the resistance of a fluid to flow
Plastic viscosity is a non-Newtonian property of fluids, referring to the fact that a fluid will not flow until a shear force is applied. Unlike Newtonian fluids, plastic fluids do not begin to flow until enough shear force is applied. Once the fluid begins to flow, the shear stress and shear rate are linearly related.
Plastic viscosity is essentially a measure of the resistance of a fluid to flow. It is used as an indicator of the size, shape, distribution, and quantity of solids, as well as the viscosity of the liquid phase. A fluid with high plastic viscosity is undesirable and could result in increased equivalent circulating density due to increased pump pressures. This, in turn, may lead to an increased amount of energy being required to pump the fluid. A high plastic viscosity can also cause an increase in torque and drag, a low bit penetration rate, and an increase in surge and swab pressures.
The plastic viscosity of a fluid can be adjusted by controlling its temperature. In general, increasing the temperature of a fluid will decrease its viscosity, making it flow more easily. Conversely, lowering the temperature will increase the viscosity of a plastic fluid. This can be useful for ensuring efficient and reliable operation in liquid transfer systems.
Mechanical shear can also be used to reduce the plastic viscosity of a fluid by disrupting its structure. Additionally, the use of specially designed additives, such as modifiers and rheologists, can change the rheological properties of a fluid, thereby adjusting its plastic viscosity.
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It is undesirable to have high plastic viscosity in drilling fluid
Plastic viscosity can be defined as the resistance of a fluid to flow freely. It is a rheological property of drilling fluids and is an important characteristic that affects the properties of drilling fluid.
High plastic viscosity in drilling fluid is undesirable and can cause a number of issues. Firstly, it can lead to an increase in torque and drag, resulting in higher energy requirements for pumping the fluid. This increase in pumping pressure can also cause an increase in equivalent circulating density. Secondly, high plastic viscosity can cause a low bit penetration rate, reducing the efficiency of the drilling process. Additionally, there is a possibility of pipe sticking, which can further complicate the drilling operation.
Furthermore, high plastic viscosity is associated with wellbore problems and can lead to an increase in surge and swab pressures. The viscosity of the drilling fluid is crucial as it can impact the rate of penetration (ROP). Low plastic viscosity at high temperatures indicates that the mud formulations are lubricious and capable of a fast ROP. Therefore, it is important to select mud formulations that retain their rheological properties and have low plastic viscosities, especially at high temperatures, to ensure their suitability for use as drilling fluids.
The plastic viscosity of a drilling fluid is influenced by various factors, including the size and concentration of solids present in the fluid. To reduce plastic viscosity, the solid contents can be decreased by diluting the mud. Additionally, the viscosity of the fluid phase also plays a role, with water-based fluids having lower viscosities than brine or oil-based fluids.
In summary, high plastic viscosity in drilling fluid is undesirable due to the resulting increase in torque and drag, low penetration rate, possibility of pipe sticking, and increased surge and swab pressures. It is important to monitor and control the plastic viscosity of drilling fluids to ensure efficient and safe drilling operations.
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Plastic viscosity affects pump selection and performance
Plastic viscosity is a non-Newtonian property of a fluid, referring to its resistance to flow. It is a measure of how much a fluid resists deformation by shear stress, such as that caused by liquid flow. This resistance is a result of friction between the liquid undergoing deformation and the solids and liquids present in the drilling mud.
In the context of pump selection and performance, plastic viscosity plays a significant role. Firstly, it affects the flow properties of the fluid being pumped. For instance, highly plastic viscous fluids require more force to initiate flow, which may result in higher energy requirements for starting the pump. This can impact pump efficiency, particularly when dealing with highly viscous fluids.
The type of pump selected is also influenced by plastic viscosity. Centrifugal pumps, for example, may not be suitable for highly viscous liquids due to reduced efficiency and increased power requirements. In such cases, PD pumps, including progressive cavity pumps, diaphragm pumps, and piston pumps, may be more appropriate choices as they are designed to handle high-viscosity fluids and provide greater torque.
Additionally, the HI method enables pump users and designers to estimate the performance of a rotodynamic pump on liquids of known viscosity, based on its performance on water. This helps in selecting the suitable pump and driver for the specific application.
Temperature control is another factor to consider when dealing with plastic viscosity. Increasing the temperature generally decreases the viscosity of a plastic fluid, making it flow more easily. Conversely, lowering the temperature increases its viscosity. Therefore, by adjusting the temperature, the plastic viscosity can be modified to suit different process requirements.
In summary, plastic viscosity significantly impacts pump selection and performance. It influences the choice between different types of pumps, the efficiency and power requirements of the pumping system, and the flow properties of the fluid being pumped. Understanding plastic viscosity is crucial for optimizing the handling of thick fluids, paints, slurries, and similar substances in industrial and chemical applications.
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It is a parameter of the Bingham plastic model
Plastic viscosity is a rheological property of fluids that describes their resistance to flow. It is one of two types of viscosity, the other being apparent viscosity. It is an important parameter in drilling engineering and slurry handling, where it is used to optimise the performance of drilling fluids and prevent wellbore problems.
The Bingham plastic model is a mathematical representation of how certain fluids behave under stress. It is named after Eugene C. Bingham, who first proposed the model in 1916. The model describes fluids that behave as rigid bodies at low stresses but flow as viscous fluids at high stresses. A common example is toothpaste, which requires a certain amount of pressure to be applied before it will exit the tube.
Plastic viscosity is indeed a parameter of the Bingham plastic model. In this model, the shear stress must exceed a certain value, known as the yield stress, to break the gelation bonding of the fluid and allow it to flow. This behaviour is described by the equation:
> Shear stress = (Plastic viscosity) x (Shear rate) + Yield stress
The Bingham plastic model is particularly useful for treating drilling fluids and understanding their behaviour. It can be used to estimate pressure loss in turbulent conditions and to identify the nature of any contamination in the drilling fluid. For instance, an increase in plastic viscosity indicates the presence of solid contamination, while an increase in the yield point could suggest chemical contamination.
The Bingham plastic model is a valuable tool in hydraulic analysis, providing a simple and accurate way to understand the flow behaviour of non-Newtonian fluids.
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Frequently asked questions
Plastic viscosity is a non-Newtonian property of a fluid, which refers to its resistance to flow. It is a measure of viscosity or high-shear-rate viscosity.
Plastic viscosity is influenced by factors such as temperature, water content, aggregate properties, and the size, shape, and quantity of solids in the fluid.
Understanding plastic viscosity is crucial for efficient liquid transfer and pump efficiency. It helps in selecting the appropriate pump system and maximising performance in industrial and chemical applications.
Plastic viscosity can be reduced by mechanical shear, which involves using equipment like agitators to disrupt the fluid's structure. It can also be adjusted by using additives that change the rheological properties of the fluid.
