Mixing equipment selection has always been a basic and difficult task, not only need to fully understand the nature of the material (including physical and chemical properties, such as viscosity, consistency, solid content, density, corrosion resistance, etc.), also need to know the purpose of mixing or stirring (for example, dissolved, suspended, aggregation, etc.), also need to know about different stirrer (pusher blade and oblique blade, ribbon, emulsification, dispersion) of the working principle and advantages and disadvantages. Good selection of agitator is the basis of technology realization.
Here are some concepts about stirring:
I. definition, nature and purpose of mixture
The operation of mixing materials uniformly in any state (solid, liquid, gaseous, and semi-liquid) is called "mixing" in theory. However, traditionally the operation of "mixing solid materials or humidifying solid materials" is called "mixing". The operation of mixing "solid, liquid or gaseous material" with "liquid material" is called "stirring".
The essence of the mixing process is a process that causes the non-uniformity of materials in the system to decrease continuously. It is a process that inputs mechanical energy into the stirring tank through the rotation of the agitator, so that the fluid can obtain the appropriate flow field (flow field), and carry out the transfer of momentum, heat and mass or chemical reaction in the flow field.
Stirring can be an independent unit operation in the field of fluid mechanics with the main purpose of promoting mixing, such as solid-liquid suspension, liquid-liquid mixing, gas-liquid dispersion, liquid-liquid dispersion and liquid-liquid emulsification. It is often a necessary means to complete other unit operations, to promote heat transfer, mass transfer, chemical reaction as the main purpose, such as fluid heating, cooling, extraction, absorption, dissolution, crystallization, polymerization and other operations.
II.stirring involves several important terms
Fluid is the general name of liquid and gas. It is composed of a large number of molecules that are in constant thermal motion and have no fixed equilibrium position. Fluid has a certain compressibility, liquid has a small compressibility, while gas has a large compressibility. When the shape of the fluid changes, there is also a certain movement resistance (i.e. viscosity) between the layers of the fluid.
The material will flow under the action of stress, and its rheological behavior has "Newtonian type" and "non-newtonian type", which depends on the structure of the material and its stress state.
Newtonian fluid: fluid in which the shear stress on a fluid is proportional to the shear deformation rate. Non-newtonian fluid: anything different from a Newtonian fluid is called a non-newtonian fluid.
Flow field (flow pattern and flow field)
Flow pattern: only the shape of streamline in the flow field is "qualitatively described", which is called "flow pattern". There are generally three basic flow types: 1. Tangential flow; 2. 2. Axial flow; 3. Radial flow. Three basic flow patterns can usually exist simultaneously, in which "axial flow and radial flow" play a major role in mixing, while tangential flow should be suppressed.
Flow field: generally, the radial and axial velocity distribution in the longitudinal section of the reactor body and the radial and axial velocity distribution in the cross-section of the reactor body are "quantitatively described", which is called "flow field". Flow field is a concept of "three-dimensional flow", which is random and very complicated.
Viscosity is generally expressed in five ways: dynamic viscosity, kinematic viscosity, engler's viscosity, redler's viscosity and saybolt's viscosity, and the latter three are called conditional viscosity (also known as relative viscosity).
Motion viscosity, said liquid under the action of gravity flow inside a measure of the resistance, with symbol υ, said the value of the dynamic viscosity of the liquid at the same temperature and the ratio of the density, in the legal system of units of measurement in m2 / s, said general was commonly used mm2／s. It is customary to use St or cSt as the non-statutory units of measurement. The conversion relation between them is: 1m2 / s = 106mm2 / s = 104St = 106cSt.
Viscosity and consistency are related to the flow and transfer performance of the fluid, and the two affect each other. Viscosity and consistency are different concepts, there are certain differences between the two, "viscous" fluid is not necessarily "thick"; And the consistency fluid is not equal to the viscosity; The greater the viscosity, the worse the fluidity.
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III. Consideration factors of mixed equipment design and selection
Based on RUMI's years of experience and research, we believe that the following elements should be considered in any hybrid device design and selection:
1. Material type: gas, solid and liquid; Phase state: liquid-liquid, solid-liquid, solid-solid and other seven.
2. Properties of the mixed material: viscosity of the fluid; Consistency; The density or specific gravity of the material; Corrosiveness, etc
3. Material quantity.
4. Mixed purpose.
5. Technological requirements or characteristics of the mixing process.
6. Analyze and study the characteristics of various agitators, especially the flow field/flow pattern generated by agitators.
7. Energy consumption or cost expenditure.
8. Other aspects, etc.
RUMI as specialized supplier in fine chemical industry (process industry) of dispersing, mixing, grinding, mixing equipment.,
Rumi has a team of engineers from chemical industry and machinery industry. They are all came from "professional class"and have many years for material mixing and reaction process of design and operation experience,
Rumi people are willing to work with research institute, college, communicate with their peers, the masses of users to learn, explore and research, especially strengthening basic theory research, and closely tracking the world development trend of mixing equipment, on the basis of the solution satisfing the requirement of technology of mixing, to offer better package solutions for users.