Classification of High-Pressure Small Homogenizer and Analysis of Homogenization Principle
The small homogenizer is using strength to break the "impossible" and mix materials that could not be evenly mixed easily. Small homogenizer has become indispensable equipment for food finishing. It is often used in combination with mixing, mixing and emulsifying machines. With the progress of science and technology, the variety of equipment used for food homogenization is becoming more and more diverse.
Diversification of Small Homogenizers
In principle, these equipment cause high pressure, extrusion impact and pressure loss through mechanical or hydrodynamic effects, so that the material can be extruded under high pressure, shear under the strong impact, and expand under pressure loss, so as to achieve the goal of refinement and mixing homogenization under the triple action. According to the structure, the homogenizer can be divided into a high-pressure homogenizer, centrifugal homogenizer, mechanical ultrasonic homogenizer, magnetron oscillator homogenizer, piezoelectric crystal oscillator homogenizer, colloid mill homogenizer and so on.
High-Pressure Small Homogenizer
1. Working Principle of High-Pressure Small Homogenizer
The high-pressure small homogenizer is a kind of material passing through very narrow clearance under high pressure (usually less than 0.1 M m), resulting in high flow rate (150-200 m/s), so that the material is subjected to strong shear force. At the same time, due to the high-speed impact between the particles in the material and the parts and the swirl effect of the liquid flow when passing through the droplet homogenizer valve, it makes the material slight. The granules are fragmented to achieve homogeneity.
At present, the mechanism of the working process of the homogenizer can be summarized as the following three theories:
1) Shear theory
According to the shear theory, fluid flows at high speed under high pressure, and through the gap of the homogenizing valve of homogenizer, droplets break up under the action of shear force to achieve homogenization.
When the droplet passes through the entrance of a very small gap under high pressure, the velocity of the droplet is V0 and the pressure is P 0. When passing through the gap, the pressure is P1 and the velocity reaches V2. The velocity of the droplet at the center of the gap is the highest, and the droplet on the wall of the gap is the smallest. The sheer force caused by the large velocity gradient makes the droplet deform and break up, and achieves homogeneity, Effect.
Usually used high-pressure small homogenizer is mainly composed of high-pressure pump and homogenizer valve. The material is sucked into the pump chamber by the plunger reciprocating pump. Under high pressure, the droplets are discharged through the homogeneous valve in the pipeline through the high-pressure pump. The material and liquid flow through the very small gap between the valve core and the valve seat at high speed. The width of the general gap is about 0.1 M m, and the flow rate is as high as 150-200 m/s.
2) Impact Theory
The impact theory holds that under high pressure, droplets in fluid collide with homogeneous valves at high speed so that droplets break up to achieve the homogeneous purpose.
3) Hole theory
According to the theory of cavitation, high-speed flow of liquid through the slit under high pressure results in high-frequency vibration, which causes rapid alternating compression and energy expansion, and causes cavitation phenomena in an instant, which breaks the droplet and achieves the goal of homogenization.
Which of the above three theories is the main one and which is the second one?
2. Structure and working process of high-pressure small homogenizer
In the food industry, the widely used high-pressure homogenizer is based on the reciprocating of three plungers as the main body and installs two-stage homogenizing valve head in the discharge pipeline of the pump. The structure of high-pressure homogenizer is mainly composed of three-plunger reciprocating pump, homogenizing valve, transmission mechanism, and shell. The machine structure combination includes control disc, transmission mechanism, homogenizing head, pump body, high-voltage meter, motor, frame, and shell, etc.
High-Pressure Small Homogenizer
1) Three-plunger reciprocating pump
Pump body structure: The pump body is cuboid with three pump chambers. The piston moves in the pump chamber to make the material suck in summer and flows to the homogeneous valve after pressurization. The pump body and piston are usually made of stainless steel. In order to prevent liquid leakage and air infiltration, filler sealing device is used. The material can be leather, asbestos rope, and polyfluoroethylene.
Each pump chamber of the high-pressure pump is equipped with two valves. The pressure in the chamber is changed by the reciprocating motion of the piston so that the valve can be opened or closed automatically alternately to complete the function of inhaling and discharging liquid. Three plunger pumps have six valves, of which three are suction and discharge valves. The homogeneous valve can adjust the spring pressure on the spool to achieve the purpose of regulating fluid pressure.
Reciprocating pump in the piston to and fro in the process of only inhaling and discharging liquid once each pump is called a single-acting pump. Because the suction valve and discharge valve of the single-acting pump are installed on one side of the piston, it can not drain when sucking, so the drainage is discontinuous. Because the piston is driven by connecting rod and crankshaft, the reciprocating motion of the piston between the left and right points is not equal speed, so the drainage volume also fluctuates with the movement of the piston. In order to improve the non-uniformity of single-acting pumps, double-acting pumps or triple-acting pumps are often used.
Working Principle of Double-acting Reciprocating Pump
Inside the pump body on both sides of the piston is equipped with suction valves and discharge valves. No matter which side the piston moves to, there will always be one suction valve and one discharge valve open. That is to say, in the reciprocating piston, the suction and drainage are carried out twice, so that the suction and discharge pipelines always have liquid flow through, so that the flow curve is continuous, but there is still a flow curve. Volts. In order to keep the discharge fluid continuous and uniform, the triple pump is usually used. The essence of the triple pump is composed of three single-action pumps in parallel, commonly known as triple plunger pump.
2) Homogeneous Valve
The working principle of homogenization valve: In general, there are two-stage homogenization valves in homogenization operation. The first stage is the high-pressure fluid. The pressure of the first stage is as high as 20-25 MPa. The main function of the homogenization valve is to make the droplets uniform and disperse. After the first stage, the fluid pressure decreases to 3.5 MPa. The main function of the second stage is to disperse the droplets. Due to the high-speed flow of high-pressure materials, the wear of valve seat and valve core (also known as valve disc or homogeneous head) is quite serious. Wear-resistant alloy steel containing tungsten, chromium, drill and other elements is commonly used and manufactured by fine grinding.
3. CALCULATION OF PRODUCTIVE CAPACITY OF HIGH-PRESSURE HOMOGENERATOR
The production capacity G of high-pressure homogenizer can be calculated by the following formula: G = 60 PI resin epsilon (m/h). R is the plunger radius, m; s is the plunger stroke, m; Z is the number of plungers; for the number of plunger reciprocating times, times per minute; and for the working volume, the filling coefficient is generally 0.8-0.9.
4. Notes for the operation of small homogenizer
(1) The small homogenizer is not allowed to idle. Before starting, it is necessary to carefully check whether the fasteners and connectors are firm and reliable.
(2) Cooling water should be supplied before starting to ensure the reliable cooling of the plunger during operation.
(3) After the start-up of the operation, the required working pressure should be gradually adjusted. The material discharged during the start-up process should be recirculated into the material chamber, and the product can be discharged only after the pressure reaches the required stable value.
(4) After the equipment is used, it should be cleaned (hot water above 90 degrees C or non-toxic chemicals can be used) and disinfected and sterilized.
(5) The packing of the plunger should be adjusted to an appropriate tightness to ensure reliable sealing.
(6) Parts requiring lubrication shall be filled with suitable lubricating oil on time.
(7) It can not be used for homogenization of high-viscosity materials.