Classification of water jet pumps:
Water jet pumps are classified according to injection mode and structure type.
A Classified by injection mode:
1) Continuous injection. The working fluid jet is continuous. At present, most water jet pumps adopt this method.
2) Swirl jet. The working fluid jet is rotating, which can increase the contact area of liquid and gas, and make the jet break up quickly and disperse into droplets, so as to improve the efficiency of the pump. The disadvantage is that the cyclone generator consumes part of the energy.
3) Pulse injection. The working fluid jet is pulsed intermittently. The pulsed jet can make the fluid mix quickly and reduce the length of mixing section. In addition to droplet collision, there are also energy transfer modes similar to piston compressor.
B Classified by structural type
A single stage
1) Single nozzle short throat tube. The single stage short throat water jet pump has small volume and simple structure, but its efficiency is lower than other types of pumps. The length of throat pipe is 5 to 8 times the diameter of throat pipe.
2) Single jet long throat tube. The length of the laryngeal tube is 10 to 60 times the diameter of the laryngeal tube.
3) Multiple nozzles. The number of nozzles ranges from 4 to 19. Because the contact area between working jet and gas is increased, the efficiency is higher.
Most of the multi-stage water jet pumps are two stages. After the first stage is sucked in, the liquid-gas mixture jet is sucked in the second stage. This can make full use of the energy of the jet to achieve the purpose of reducing the limit pressure of the pump.
The structure of water jet pump:
The function of the nozzle of water jet pump is to transform the pressure energy of water into kinetic energy. Its structure has a great influence on the performance of the pump. Common forms are conical contraction nozzle, circular thin-walled orifice nozzle, streamlined nozzle and porous nozzle, etc.
B inhalation room
The suction chamber is connected with the intake pipe. The suction chamber is usually cylindrical, and its cross section is 6-10 times of the nozzle outlet area.
The diffuser consists of three parts. The function of the gradual contraction section is to make the exhausted gas enter the throat smoothly, and its contraction half angle is beta=15 ~30. The throat tube makes liquid and gas mix evenly for mass and energy transfer, and its cross section is circular. The progressive expansion section transforms the kinetic energy of the liquid-gas mixture into the pressure energy, which compresses the extracted gas, and its progressive expansion angle is between 5 and 8 degrees.
Compared with the diffuse jet pump, the pumping capacity and the maximum outlet pressure of the oil diffuse pump are much lower, so the heating power of the pump is also lower. The diameter of the oil diffusion pump boiler is usually equal to (less than) the diameter of the pump mouth. The heat load of oil diffusion pump boiler with pumping speed greater than 500L/S does not exceed 2-2.5W/cm2.
In oil diffusion pumps, the power consumed by oil evaporation is usually 60% to 70% of the total power, and the rest is the power to compensate for various heat losses. In diffusion pump, heat loss mainly includes the following aspects: heat transfer from heater surface to outside through boiler wall (20% - 25%), heat transfer from heater wall to cooling pump body (10% - 15%) along pump wall; radiation from diversion tube surface to pump wall and heat transfer of mixture of gas and steam from diversion tube to pump wall (5% - 10%). If the result of the pump is good, the heat loss can be reduced to 10% - 15% of the total power. For example, insulating the heater of the pump and the boiler can obviously reduce the heat loss. If the closed heater is used, there is no air layer between the bottom of the boiler and the heater, then the heating power can be well utilized.