Investigations On The Low Pressure And Mass Flow Atomizer For Spray Icing

The effervescent atomizer is widely used in combustion,spray cooling,spraying and fire extinguishing because of its simple structure,high atomizing quality,and low energy consumption.In order to further expand the application field of effervescent atomization,a low-pressure and small-flow effervescent atomizer is investigated in this thesis for spray freezing.Firstly,an effervescent atomizer with an internal swirl and wire mesh bubble cutting structure coupling was designed in this thesis.After the initial mixing of gas and water in the primary mixing chamber,the gas and water entered the secondary mixing chamber through multiple swirling channels.Then,the gas-liquid two-phase fluid was cut into uniform bubble flow by a metal wire mesh,and was ejected through a special-shaped atomizer.Secondly,the flow characteristics of the effervescent atomizer were experimentally studied in this thesis.The working pressure,gas liquid mass flow ratio(ALR)and atomizer cross-sectional area are main factors for affecting the spray flow.The spray flow increases with the increase of working pressure and the atomizer cross-section area.However,the increase of the gas liquid mass flow ratio(ALR)has an opposite influence.The flow gradually decreases with the increase of ALR,when the flow coefficient of the effervescent atomizer was about 0.1.Thirdly,the atomization characteristics of the inner swirling effervescent atomizer were diagnosed and analyzed by Malvern laser particle size analyzer.The main factors were working pressure,ALR and nozzle orifice shape for affecting the atomization quality.The increase of ALR would help improve the atomization quality and reduce the average diameter of atomized particles in the same working pressure.The increase of the working pressure could significantly improve the atomization quality in the same ALR.The special-shaped atomizers,especially square atomizer and scaled atomizer could achieve better atomization than circular atomizer in the same working conditions.The results show that strengthening the atomizer disturbance can help promote the bubbles breakup.Then,the internal flow characteristics and external spray characteristics of the effervescent atomizer were investigated by the high-speed camera and the laser phase Doppler interferometer(PDI).The visual images showed that the wire mesh helps to transform the slug flow into a bubbly flow.The spray diagnosis results showed that the atomization quality was improved after coupling the bubble cutter and the average particle diameter D₅₀ was reduced by about 2?m.Finally,the energy consumption of the effervescent atomization was theoretically analyzed in this thesis.The gas expansion and the viscous dissipation were the important energy consumption,which account for 46%and 30%,respectively.Therefore,the improvement of the atomizer should focus on the decrease of the expansion consumption.The research results in this thesis have satisfied the various technical requirements for the project commissioner,and the relevant data provide guidance for the design and application of the effervescent atomizer.