What Is Two-Phase Flow?
A two-phase substance (at least one of which is a fluid) is a flow system. If there are more than two phase states of a substance in a flow system, it is called multiphase flow. Two-phase or multiphase flow is the most common viscous fluid flow involved in chemical production to complete the interphase mass transfer and reaction process. Heat transfer during phase changes, gas absorption in column equipment, liquid distillation, liquid extraction, and chemical reaction processes in stirred tanks or bubble columns all involve two-phase flow.
- Chinese name
- Two-phase flow
- Foreign name
- two phase flow
- Field
- Nature and other engineering fields
- Category
- Engineering technology
- A two-phase substance (at least one of which is a fluid) is a flow system. If there are more than two phase states of a substance in a flow system, it is called multiphase flow. Two-phase or multiphase flow is the most common viscous fluid flow involved in chemical production to complete the interphase mass transfer and reaction process. Heat transfer during phase changes, gas absorption in column equipment, liquid distillation, liquid extraction, and chemical reaction processes in stirred tanks or bubble columns all involve two-phase flow.
two phase flow Two -phase flow
- Two-phase flow also exists widely in nature and other engineering fields, such as: rain, snow, clouds, and fog, blood circulation in organisms, sediment movement and high-speed aerated water flow in water conservancy projects, and soot and dust in environmental engineering Air pollution, etc.
Two- phase flow type
- Generally, it is divided into gas-liquid system, liquid-liquid system, liquid-solid system, gas-solid system, etc. according to the phase states constituting the system. The gas and liquid phases can appear as continuous phases, such as gas-liquid film systems; they can also occur in discrete forms, such as bubble-liquid systems, droplet-gas systems. The solid phase is usually in a two-phase flow in the form of particles or agglomerates.
- Two-phase flow has various flow patterns. In addition to the distinction between laminar and turbulent flow as in single-phase flow, it can also be based on the relative content of two phases (commonly referred to as phase), the distribution characteristics of the phase interface, the speed of movement, and the geometric conditions of the flow field (inside the tube, perforated plate, edge Wall surface, etc.) to divide the flow pattern. For the gas-liquid system in the tube, with the change of the two-phase velocity, it can produce bubble flow, plug flow, laminar flow, wave flow, impinging flow, ring flow, mist flow and other forms; Generates freely dispersed bubbles, honeycomb foam, movable foam, spray, etc.
Study of two- phase flow
- One of the basic topics of two-phase flow research is to judge the flow patterns and their mutual transformation. Different flow patterns have different mechanisms and influencing factors for heat and mass transfer. For example, when the gas-liquid two-phase in a porous plate is in a bubbling state, the plate efficiency (see grade efficiency) of the positive system mixture (the surface tension decreases when the concentration increases) is higher than that of the negative system mixture (the surface tension increases when the concentration increases); and the spray state It's exactly the opposite. Another basic topic in the study of two-phase flow is the motion of the dispersed phase in the continuous phase and its effect on the transfer and reaction processes. When dispersed phase droplets or bubbles have many characteristics. For example, droplets and bubbles will deform during movement, there will be circulation in the droplets or bubbles, fluctuations on the interface, and surface tension gradients will cause complex surface movements. These will affect the mass transfer flux and thus the performance of the device. The research topics of two-phase flow include frictional resistance, oscillation and stability of the two-phase flow system.
Method for studying two-phase flow
- The theoretical analysis of two-phase flow is much more difficult than single-phase flow. The general differential equations describing two-phase flow have not yet been established. A lot of theoretical work uses two types of simplified models: homogeneous model. The two-phase medium is regarded as a very homogeneous mixture. It is assumed that the concepts and methods for processing single-phase flows are still applicable to two-phase flows, but reasonable assumptions must be made about its physical properties and transmission properties; phase separation model. It is considered that the concept and method of single-phase flow can be applied to each phase of a two-phase system separately, while considering the interaction between the two phases. There are still many difficulties in the application of both models, but there has been considerable progress driven by the development of computing technology.
- The experimental study of two-phase flow is the basic method to master the law of two-phase flow. At present, optical methods (including light absorption, scattering, interference, refraction, etc.), other radiation absorption and scattering methods, tracer methods, and capacitance and conductance methods are widely used to determine important parameters in two-phase flow, such as pressure, porosity, Average film thickness, droplet diameter, and movement speed. In a sense, a deeper understanding of the law of two-phase flow depends on the advancement of experimental technology.