Abstract:
Because they can reduce fluid flow energy consumption, drag reducing agents are widely used and promoted as important energy-saving tools. In particular, polyethylene oxide is used as a good drag reducing agent. Focusing on the drag reduction effect of polyethylene oxide, here is mainly discusses and analyzes the change law of the drag reduction rate of polyethylene oxide under the influence of some factors. These influencing factors include concentration, temperature, molecular weight, solubility, Reynolds number, injection method of drag reducing agents in the pipeline, actual equipment along the pipeline, etc.
This article mainly explains the current representative theory of drag reduction. A preliminary explanation of the drag reduction mechanism of polyethylene oxide is made. Later, we will elaborate on the application of DRAs in the fields of oil and gas, coal mining and transportation, and the energy-saving benefits they bring.
The performance optimization of polyethylene oxide and the drag reducing agent encapsulation technology have become hot topics in applied research. This DRA is expected to be applied in more fields and more complex environments in the future. In order to achieve a better energy-saving effect.
Content Table:
Overview:
According to big data, the demand for global energy will increase by 25% to 40% from current levels by 2050. Use existing technology to achieve energy conservation and improve energy utilization, in order to delay the expansion of energy demand. This has become an important direction for nowadays research and exploration.
In the fields of oil and gas, many companies often use various types of drag-reducing agents to reduce energy loss during fluid flow. Drag reducers are divided into oil-soluble DRA and water-soluble DRA. The oil-soluble drag reducing agents widely used at present include polyisobutylene, olefin copolymers, poly long-chain α-olefins, polymethacrylates, and the like. The water-soluble drag reducing agents include polyethylene oxide, polyacrylamide, xanthan gum, guar gum, saponin powder, Tianqing powder locust bean, and so on. Polyethylene oxide has great application potential due to its superior drag reduction ability, stable properties, and low cost.
In order to master the change rule of resistance reduction performance of polyethylene oxide more comprehensively. Grasp the current direction of its applied research. IRO will analyze in detail the influence of various influencing factors on the drag reduction performance of polyethylene oxide and the change law of its drag reduction rate. Summarize its drag reduction mechanism and current drag reduction and energy-saving applications. Prospect the development direction and trend of polyethylene oxide research.
Drag Reduction Theory
Since Toms discovered the drag reduction phenomenon, people have begun a lot of experimental research and theoretical analysis on the drag reduction phenomenon and mechanism of polymer DRA. At present, there is no accepted theory that can reasonably explain all the drag reduction phenomena. The following will introduce several representative drag reduction mechanisms.
1. Pseudoplastic Theory
Toms’ earliest point of view on the drag reduction mechanism of polymers. Toms believes that the polymer solution is a shear-thinning fluid with pseudoplastic properties. Its surface viscosity will decrease with the increase of shear rate, resulting in a drag reduction effect. This increases the drag reduction rate. Eventually, this theory was overturned. Because of its large calculation error, and Walsh study found that dilatant fluid also has a good drag reduction effect under alkaline conditions.
2. Viscoelastic Theory
The viscoelasticity of the polymer drag-reducing agents solution interacts with the turbulent vortex to produce drag reduction. Polyoxyethylene is enriched in the tube wall to form an elastic bottom layer. The elastic layer absorbs most of the kinetic energy of turbulent vortices and converts it into elastic energy for storage. This greatly reduces the energy loss caused by turbulent vortices.
3. Effective Slip Theory
The fluid flows in the tube and forms a viscous bottom layer, an elastic layer, and a turbulent core layer. Through experimental research, Virk found that the velocity distribution curve of the turbulent core area shifted upward, and the phenomenon of “effective slip” appeared. And when the thickness of the elastic layer expands to the center of the tube as the concentration of the drag reducing agent increases, the drag reduction rate reaches the maximum value. However, this theory cannot explain the problem of resistance rise when the concentration of DRA exceeds the concentration where the maximum drag reduction occurs.
4. Turbulence Suppression Theory
Polymer molecules can rely on their own viscoelasticity to make molecular chains extend naturally in the direction of tube flow. However, the turbulent fluid micro-elements have violent axial and radial pulsations and migration in the pipeline. Thereby forming a turbulent vortex. The fierce interaction between fluid microelements increases flows resistance and energy consumption. Radial irregular migration and pulsation of turbulent fluid are used on DRA molecules. Distorts its molecular chain. The molecular force of the drag-reducing agent reacts to the turbulent micro-elements, which generates an elastic force that hinders the pulsation of the fluid micelles. This causes the radial velocity of the fluid micelle to decrease and axializes part of its radial force. It greatly reduces the turbulent energy dissipation of the fluid and achieves a macroscopic drag reduction effect.
5. Decoupling hypothesis of turbulent pulsation
Polymer drag reducing agents have the ability to weaken the correlation between radial and axial pulsations of turbulent fluids. This ability is called “decoupling” by scholars. The decoupling effect of DRA reduces the turbulent pulsating Reynolds shear stress. The FIK formula derived from Fukagata is known. The reduction of Reynolds shear stress will reduce the friction coefficient. This produces a drag reduction phenomenon. Subsequent experiments confirmed that the reduction of Reynolds stress was caused by the suppression and decoupling of turbulent pulsation.
Conclusion
Based on the latest research and application achievements and progress, the changes of polyethylene oxide drag reduction performance under the influence of various factors were analyzed in detail. Looking forward to the research and development direction and trend of polyethylene oxide.
(1) In the current research of many drag reducing agent theories, the turbulent drag reduction mechanism represented by the theory of turbulence suppression and turbulent pulsation decoupling is still more recognized by the public. Both of these theories hold the view that the DRA achieves the drag reduction effect by changing the turbulent structure.
(2) At present, polyethylene oxide has been widely used in drag reduction in the fields of oil and gas and mining. And brought considerable economic and social benefits.
(3) Polyoxyethylene has the disadvantage of being vulnerable to shear damage. This requires performance optimization. Its resistance to mechanical shear can be improved by grafting polyethylene oxide with a shear-resistant substance or adding surface-active drag reducers. At the same time, the development and preparation of microcapsule polyethylene oxide DRA are one of its new research and development directions.