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Multiphase Flow Meters Section 1: Introduction Due to the wide range of applications and importance of multiphase flow systems in both natural phenomena and industrial processes, especially in the second half of the 20th century, the rapid development of nuclear power plants and the aerospace industry, the adoption of higher operating parameters in the power and petrochemical industries, as well as the growing emphasis on environmental protection, research in the field of multiphase flow has advanced rapidly. It has now become a cutting-edge discipline that receives significant attention both domestically and internationally. However, due to the complexity and randomness of multiphase flow, in order to understand phenomena, acquire concepts, develop models, and predict, design, and control processes, the first issue that needs to be addressed is the detection of multiphase flow parameters. In many cases, multiphase flow testing techniques have become a limiting factor in current multiphase flow research. Multiphase flow rate is a fundamental parameter among multiphase flow parameters, and it represents a challenge and focus that needs to be addressed urgently in industrial applications. I. Definition and Classification of Multiphase Flow A phase generally refers to a homogeneous portion of a system with the same composition as well as the same physical and chemical properties; there are distinct interfaces separating different phases. Multiphase flow — Macroscopically, matter in nature can generally be divided into three phases, namely the gas phase, the liquid phase, and the solid phase. The flow of a single-phase substance is called single-phase flow. So-called two-phase flow or multiphase flow refers to the flow of two or more different phases of matter existing simultaneously. The common multiphase flows in industry include the following, among which two-phase flow is the most prevalent. (1) Gas-liquid two-phase flow: Industrial examples of gas-liquid two-phase flow can be found in vast numbers of applications, such as in vaporization units like boilers, in the transportation of petroleum, natural gas, and low-boiling-point liquids, as well as in various separation and reaction processes in heat and mass transfer equipment. (2) Gas-solid two-phase flow: Industrial examples of gas-solid two-phase flow can be found in air-drying units such as dryers, in the pneumatic transport of coal powder, cement, grains, table salt, etc., as well as in fluidization technologies such as the bubbling combustion of coal, the catalytic cracking of petroleum, and the fluidized burning of minerals. (3) Liquid-solid two-phase flow: Industrial examples of liquid-solid two-phase flow are widespread in the flow of slurries such as mineral slurries, paper pulp, mud, and glue, in the hydraulic transport of ores and residues, and in sewage treatment and discharge systems. (4) Liquid-liquid two-phase flow: In the extraction process for substance separation, it is mostly a liquid-liquid two-phase (component) flow system in which the substances are immiscible with each other. (5) Gas-liquid-liquid and gas-liquid-solid multiphase flows: Industrial examples of multiphase flow are also common in crude oil systems at wellheads in onshore or offshore oil fields, as well as in trickle-bed and slurry reactors used for oil hydrogenation and refining, and in suspended-bed reactors used for chemical synthesis and biochemical reactions. II. Characteristics and description of multiphase flow parameters In multiphase flow, there are interfacial effects and relative velocities between the different phases. The phase interface is randomly variable in both time and space, which renders its flow properties far more complex than those of single-phase flow systems, and it also has more characteristic parameters than single-phase flow systems. For example, the presence of interphase velocity causes the ratio of phase flows passing through the pipe and the ratio of the pipe cross-sectional area occupied by each phase to be unequal. Therefore, to describe multiphase flow parameters, some new parameters need to be introduced. For the convenience of discussing the issues, the relevant parameters involved in the two-phase flow rates and a brief overview of the calculations are presented below. 1. Flow pattern The flow pattern, also known as flow regime, refers to the form or structure of fluid flow. The randomly variable phase interface existing between the two phases results in a wide variety of flow patterns in these phases, making the situation highly complex. The flow pattern is an important factor affecting the pressure loss and heat transfer characteristics of two-phase flow. On page 185 of two-phase flow, the accurate measurement of various parameters often also depends on an understanding of the flow regime. Although flow pattern research has a history of several decades, there is still no unified classification of flow patterns; even flow patterns with the same name have inconsistent definitions. Table 7.1 is presented below, listing the common flow patterns in horizontal and vertical pipes under unheated conditions for gas-liquid, gas-solid, and liquid-solid two-phase flows.