Cause analysis of the hottest flocculation power

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Coagulation is the key in the coagulation, sedimentation and filtration processes of water purification and wastewater physicochemical treatment. Practice has proved that the reasonable selection of coagulation process in the design can not only improve the effluent quality, but also achieve the purpose of saving energy and reducing operating costs. It is the key to improve flocculation efficiency to understand the dynamic cause of flocculation, but the dynamic cause of collision of small particles in water flow has not been clear, so it is necessary to conduct in-depth research. 1 flocculation dynamic factor flocculation generally refers to the process that colloids in water contact and collide with each other after adding coagulant for destabilization, and grow into large flocs under the action of attraction. To study the dynamic process of flocculation, that is, to study the change of particle state in the process of flocculation, and how particles gradually evolve from smaller particle size with more quantity to larger particle size with less quantity. The primary condition for flocculation of particles is contact collision. There are three main ways for contact collision of particles in water: Brownian motion of particles; Sedimentation velocity difference between particles; Hydraulic action of flowing water body

in unit volume and unit time, the number of particle contact collisions NB caused by Brownian motion can be expressed as: (1) where k is the Boltzmann constant; T is the absolute temperature; μ Is the dynamic viscosity of water, and N is the number of particles per unit volume

the particle collision rate caused by Brownian motion is proportional to the water temperature and the square of particle wear rate (V) and particle concentration, but independent of particle size. In fact, only small particles have Brownian motion. With the increase of particle size, Brownian motion will gradually weaken. When the particle size is greater than 1 micron, Brownian motion will basically disappear [2]. For the general flocculation tank, the floc particles generally increase from micron to millimeter, so the particle contact collision caused by Brownian motion can be ignored

the number of particle contact and collision NC caused by sedimentation velocity difference in unit volume and unit time can be expressed as: (2) as for particle contact and collision caused by sedimentation velocity difference, it often plays a certain role in the sedimentation tank, while in the flocculation tank, due to the strong turbulence of water flow, the role of sedimentation velocity difference will be relatively small. Especially in the initial stage of flocculation, the particles are still small, and their settling speed is not large. If they are unqualified, the red word "unqualified" will be displayed and an alarm will sound, so the settling speed difference between different particles will be smaller. Therefore, the contact collision caused by the settling speed difference can generally be ignored in the flocculation tank [2]. Based on the above analysis, it can be concluded that the hydraulic effect of flowing water plays a leading role in accelerating particle flocculation. Flocculating kinetic induced turbulence is a random and irregular movement. A true description of this irregular movement is an important way to understand the characteristics of turbulence. However, it is difficult to give a complete description of the complex motion of turbulence, and only an approximate idealized model reflecting the main characteristics can be proposed. At present, Richardson kolmerov has been accepted by everyone Колмогоров) Turbulence image of. The description is as follows: in the fully developed turbulence with very high Reynolds number, there are pulsations or vortices or disturbances of various frequencies, amplitudes and periods, that is, the fully developed turbulence is composed of vortices of various scales. The mean flow loses its stability and decomposes into a first-order vortex, which is powered by the mean flow; The first-order vortex body is decomposed into the second-order vortex body and provided with energy until the minimum scale vortex dissipates the energy consumption first, that is, from mechanical energy to non mechanical energy. From this turbulence image, the turbulent motion can be seen as the result of the superposition of vortex motion with different scales on the average velocity beam, and the shear force and inertial centrifugal force generated by vortex motion are the main dynamic causes of particle contact and collision. 2.1 the vortex motion law in the turbulent motion of vortex shear flocculation

can be expressed by the following formula: (3) in the formula: u is the tangential velocity of the calculation point; 2. It is appropriate to take the tangential velocity of high material temperature and high mold temperature; K is a constant; M is the index, generally M = 0.5 ~ 0.9; R is the distance from the calculation point to the origin, that is, the vortex radius. Then the velocity gradient at radius r, i.e. plastic deformation Sr, is: (4) heisenbery proposed that even turbulent flow can be regarded as mean flow to study its characteristics, which is consistent with cross's view that turbulent flow can be modeled as a combination of some complex laminar motions. With the help of camp's Flocculation equation, the collision times NIJ of I and j particles in unit volume of water per unit time caused by vortex velocity gradient can be expressed as: (5) in the formula, Ni is the concentration of I particles; NJ is J particle concentration; RI is I particle radius; RJ is J particle radius; Other symbols are the same as before& n

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