What Is Polyphagia?

Polyphase has several AC electromotive forces in AC power lines with the same frequency but different primary phases. There are more than two connectors for external power supply.

What we mean by polyphase is generally three phases. A three-phase generator is used as a power source, which is called a three-phase power supply; a circuit powered by a three-phase power source is called a three-phase circuit; U, V, and W are called three phases, and the voltage between the phases is the line voltage. It is 380V. Generators with the same amplitude, frequency, and phase difference of 120 ° are called three-phase generators;

The three-phase power is mainly used as the power source of the motor, that is, the load that needs to rotate. Because the three phases of the three-phase power are all 120 degrees, the rotor will not jam.

Imagine: one pedal of the bicycle is stopped at the bottom and the other is at the highest position. At this time, the foot force of stepping on the bicycle is downward, and it may be "stuck" (when the direction of the foot force is consistent with the connection of the two pedals), Turning backwards does not necessarily ensure that you turn forward first, and you need to change the angle of the pedal with your feet.

Three-phase power is to form this "angle", otherwise, people do not need to engage in such complicated three-phase power.

Three-phase electricity has only one more wire than two-phase electricity, but the energy transmitted is three times the original. In addition, three-phase electricity is the minimum number of phases that can directly generate a rotating magnetic field with "directional determination and a starting torque."

Three-phase electricity 380 volts. Single-phase electricity 220 volts. The so-called three-phase power refers to the three-phase live line, and the voltage between adjacent live lines is 380V. There is no neutral line. Therefore, the three-phase power can only be applied under the same situation of three-phase load (for example, three-phase motor). The sum of the current vectors of the phase power is 0 (the three-phase power forms a 120-degree angle with each other, so the sum is 0). At this time, the neutral line (equivalent to the neutral line) is not required.

The power generated by the generator is three-phase. Each phase of the three-phase power and its neutral point can form a single-phase loop to provide users with electrical energy. Note that the AC circuit cannot be called positive or negative in this circuit. It should be called line end (fire line in civil power) and neutral line (neutral line in civil power).

Three-phase power can provide a more reasonable power source. As a motor energy source, there is no need for other things. As long as the three-phase power is directly connected to the motor, the motor can run. If it is a one-way motor, you need to add a complicated thing to the motor to ensure that the motor runs.

The three-phase asynchronous motor consists of a stator and a rotor, and its stator winding is a three-phase symmetrical winding, which uses a symmetrical power supply.

A two-phase motor designator has a two-phase motor. Two-phase motors are divided into two categories: drive and servo. (Single-phase) asynchronous motors used in most home appliances and small appliances are two-phase drive motors. Two-phase servo motors for control. The two-phase windings of the stator are the excitation winding and the control winding, respectively. The electrical phase difference is 90 degrees in space.

A discipline that studies the mixed flow of gaseous, liquid, and solid materials. "Phase" refers to different physical states or different physical or mechanical states of the same physical state. In the energy, water conservancy, chemical, metallurgical and other industrial sectors, as well as in the fields of meteorology, biology, and aerospace, there are problems with multiphase flow.

Multiphase flow is common in two phases of various forms. (1) gas-liquid two-phase flow, such as: aerated water flow in leaking buildings; (2) gas-solid two-phase flow, such as air transport (injection) powder, dust-containing atmospheric flow, etc .; 3) Liquid-solid two-phase flow, such as sandy water flow in natural river channels.

The history of the development of multiphase flow can be traced back to the 1870s, until the 1940s the term two-phase flow began to appear in the literature; the 1974 issue of the International Journal of Multiphase Flow; the publication of the Multiphase Flow Manual in 1982; gradually formed An independent discipline-multiphase flow. [1]

Multiphase flow discipline studies multiphase fluid flow dynamics, thermodynamics, heat and mass transfer, combustion, chemical and biological reactions, and related industrial processes with coexistence of two or more different phases or components The common scientific problem in China is an emerging cross-science that has gradually developed from the field of traditional energy conversion and utilization. It is energy, power, nuclear reactor, chemical industry, petroleum, refrigeration, low temperature, renewable energy development and utilization, aerospace, environment The important theories and key technical foundations for modernization in many fields, such as protection and life sciences, play an irreplaceable role in the foundation of the national economy and pillar industries, as well as in the development of national defense science and technology. Also in the natural world and cosmic space, the human body and other biological processes also exist a variety of complex multiphase flows. Such as the wind and cloud meeting, wind and sand storms, snow and rain, earth and earth, and cavitation waterfalls common on the surface of the earth and the atmosphere; the formation and migration of geology and mineral deposits; the origin of life and the healthy development of humans; the changes and protection of ecology and the environment And sustainable development and utilization, all generally follow the basic theories and laws of multiphase flow science. Therefore, the development and progress of multiphase flow science is of great significance to the development of national economy and national defense science and technology, human health, ecological, environmental changes, protection, sustainable development and utilization. [2]

The discipline of multiphase flow is not only as important as basic science such as purely mathematical and physical sciences such as material structure and elementary particles, chemistry, and life sciences, but also a discipline with special advantages in ordering and ordering human activities. Multiphase flow and its heat and mass transfer belong to the technical basic science category, which aims to solve the general thermophysical problems of engineering and is a bridge connecting engineering and basic theory. The development of multiphase flow disciplines will be based on the current status and development trends of natural sciences and engineering, and will foresight select advanced research topics, open up new fields, and arm the industry with new concepts, theories, technologies, and methods to drive it forward. [2]

Energy is the material foundation on which human beings depend for survival and development. The level of energy consumption and utilization is an important indicator of a country's national economic development and people's living standards. Ensuring the security of energy supply is an important goal of governments around the world. Many processes of efficient energy extraction, cleansing, and renewable transformation and utilization are typical multiphase flows and their transfer processes. There are a large number of basic scientific problems such as multiphase flows, heat transfer, mass transfer, chemical and biological reactions, such as Phase distribution and phase motion of multiphase flow, dynamics of discrete phase particles and deformed particles, laws and limits of flow heat transfer in ultra-high parameters and complex geometric flow channels, flow heat transfer and critical and supercritical effects in transient processes, Thermodynamics and micro-multiphase flow dynamics of heterogeneous continuous reaction systems, heterogeneous multiphase flow photochemistry and thermochemistry, etc. Although people have carried out a lot of research in the above fields and obtained many meaningful results, so far, they have not fundamentally grasped the basic laws of multiphase flow and its transfer process and their mathematical description methods, and carried out the above basic scientific problems. Research is necessary. [2]

(1) Establish a multiphase flow model and basic equations, analyze the pressure, velocity, temperature, apparent density, volume fraction, size and distribution of suspended solids, etc. in each phase; study the pressure drop, stability, and criticality of multiphase flow States, and phase interactions. In the 1970s, Drew (1971), Ishii (1975), etc. derived the basic equations of two-phase flow through strict mathematical deduction from the basic conservation principles, but they were not widely accepted. The common methods at this stage are: Two-fluid model. For the cases where the two comparative examples are equivalent, the respective mathematical and physical equations of the single phase are established, which take into account physical factors such as resistance, relative displacement, momentum and heat exchange (transfer) between the phases; homogeneous model. For two-phase blended uniform flow, it can be generalized into a homogeneous (continuous medium) model and a diffusion model, and analysis is carried out using classical hydraulic methods; statistical group model. For particle (bubble, droplet, and solid particles collectively referred to as particles) suspension two-phase flow, a random analysis is used to establish a statistical group (particle group) model.

(2) The experimental measurement is performed with the help of physical models. The measurement technology is very important. Many new instruments and technologies have been applied in multiphase flow testing. For example: Observing flow patterns, high-speed photography of flow patterns, holography, flow display technology, etc .; laser velocity meter (LDV), particle image velocimetry technology (PIV), etc. for measuring velocity; fiber optic sensors ( Probe), the Bp neural network system is used to measure the concentration of solid particles in the air stream, the radioisotope method is used to measure the average concentration of the section, and so on. The China Metrology and Testing Society established the "Multiphase Flow Testing Professional Committee" in October 1992, and has held several academic conferences to promote the development of multiphase flow testing technology ^[1] .