Study Of Line Pressure Characteristics And Piston Dynamic Response Characteristics Of A Pulsating Energy Exchanger

Reverse osmosis desalination technology is one of the methods to solve the freshwater crisis,which requires the use of high-pressure piston pumps to pressurize seawater to 6-7 MPa to overcome the osmotic pressure of seawater.And the flow pulsation caused by the discrete annular distribution and periodic movement of the piston is the inherent characteristic of the piston pump,which will cause pressure pulsation after interacting with the downstream load component.Therefore,the seawater pressurized by the high-pressure piston pump has the characteristic of pressure pulsation,which will cause damage to the performance of the reverse osmosis membrane module and the stability of the entire desalination system.On the other hand,reverse osmosis desalination will produce a large amount of concentrated brine,the flow rate of which can reach about 40% of the inlet water flow.Traditional methods of concentrated brine treatment have a negative impact on the environment.For example,the discharge of concentrated brine usually causes a local increase in seawater temperature,a decrease in seawater dissolved oxygen concentration,disrupts the ecological balance of the water body,and increases the corrosiveness of seawater.In order to eliminate the pressure pulsation in the pipeline,protect the reverse osmosis membrane system while solving the problem of concentrated brine discharge in the desalination process and reduce the cost of fresh water production,and achieve the effect of double-effect energy saving,the group has designed the first pulsation energy exchanger to couple the desalination system and the spray evaporation salt production system,and transfer the unfavorable pulsation caused by the high-pressure piston pump on the seawater side to the spray evaporation salt production system to create the favorable pulsation airflow required for salt production on the air side.The pulsating airflow required for the air-side salt production is favored.In order to study the characteristics of pressure pulsation in the pipeline and explore the best pulsation conditions,this paper studies the working principle of the pulsation energy exchanger by using numerical simulation method,and explores the conversion law of converting high pressure water pulsation energy into piston mechanical energy and then into air pulsation energy,to set the stage for the utilization of pulsation energy and the inverter design of the pulsation energy exchanger.The main research contents and conclusions of this paper are as follows:1.For the high-pressure sinusoidal pulsation condition of the internal pipeline of the pulsating energy exchanger,the high-pressure pipeline model of the internal pulsating energy exchanger under this condition is established,and the pulsating energy transfer characteristics under this condition are studied by numerical simulation method.The results show that under the high pressure sinusoidal pulsation condition,the pulsation energy exchanger can convert the pulsation energy into mechanical energy and has a good attenuation effect on the pressure pulsation in the pipeline.At K = 100 N/mm pulsation energy conversion effect is best.When the relative amplitude of pulsation is 0.8 and the pulsation frequency is 0.4 Hz,the pulsation energy conversion and the attenuation effect of pressure pulsation in the pipeline are the best.2.For the sinusoidal pulsation condition in which the inlet pressure of the high-pressure line gradually increases,a dynamic grid UDF program is written and the pulsation energy conversion characteristics under this condition are studied by numerical simulation.The results show that the pulsation energy can be effectively converted into piston mechanical energy under the inlet pressure increasing sinusoidal pulsation condition,and the pulsation energy conversion effect is better under the condition of low spring elasticity coefficient,high pressure,high amplitude and high frequency.3.The process of creating pulsating airflow by piston motion was studied using numerical simulation,and a model of the piston action on the airflow in the tube was established.The disturbance law of uniform airflow by different inlet speed,piston motion amplitude and frequency was analyzed.The results show that the piston reciprocating motion can effectively pulsate the uniform airflow in the pipeline.The amplitude and frequency of airflow pulsation in the pipeline are not affected by its inlet speed.The piston motion amplitude and airflow pulsation amplitude are linearly related,and the pulsation conduction efficiency is up to 99.20%,which decreases with increasing piston amplitude.The airflow pulsation varies with the same frequency as the piston motion.