Research On The Theory And Application Of Microwave Heating To Enhance The Flash Evaporation Process

Evaporation is one of the basic process units used in the chemical industry,metallurgy,energy,and water treatment.Flash evaporation is a special process unit used in the evaporation process,which is often combined with multi-effect evaporation and multi-stage evaporation.The high-temperature depletion steam generated by flash evaporation is often used as the secondary heat source.In this way,with the full use of energy,the investment cost of the equipment and the operating cost of the process are reduced.However,this method has the limitations of lengthy equipment,complicated structure,and easy scaling.Since flash evaporation occurs in a low-pressure vacuum environment,neither thermal convection nor heat transfer can rapidly heat the liquid in real time.Therefore,choosing a non-contact heating method to provide real-time in situ replenishment of flash heat loss has certain practical significance for improving the flash evaporation effect.Microwave heating has the characteristics of body heating,fast heating speed,uniform heating,non-contact,etc.,and the medium's absorption of microwaves is performed on the surface and inside at the same time.In the context of flash evaporation,the microwave is used to heat the liquid in the flash chamber,in order to increases the evaporation effect,reduces the process flow,simplifies the equipment configuration,and reduces the investment cost.In this work,the microwave flash test system was designed and developed by ourselves.The system was formed by the combination of microwave generation system,microwave induction system,flash evaporation system,condensation system,data measurement system,control system,vacuum system and connecting pipeline.With the conditions of microwave power 0.81kW-1.35 kW,liquid flow rate 10L/h-40L/h,liquid inlet temperature 40°C-60°C,and system vacuum degree 0.075 MPa.Experimental results were shown by used water as the working fluid.For the microwave flash system,in the optimized conditions of microwave power 1.35 kW,liquid flow 40 L / h,vacuum degree 0.075 MPa,Microwave and conventional conditions of the two experimental results show that under microwave conditions,the evaporation of condensing water is twice the normal operating conditions,single-stage microwave flash can achieve two levels of conventional flash replacement.A real-time comparative study was conducted on the temperature and pressure of the flash chamber.The results showed that the temperature and pressure of the flash chamber under the microwave conditions were higher than those of the normal conditions.The non-dimensional feature numbers NEF,Ja,GOR,etc.were used to characterize the flash evaporation process.It was proved that the thermal change under microwave conditions was more severe than that under normal conditions.At the same time,according to the principle of energy balance and mass balance principle,the heat balance equation of microwave flash evaporation process is established.Based on the equation and experimental data,the thermal efficiency of microwave flash evaporation process under different test conditions is calculated,under the optimal conditions,the electro-thermal conversion efficiency of system is 76.66%?...