Enhanced Mixing By Artificially Induced Internal Waves In Stratified Water Environments

Aiming at the present status of lacking the study on the relative strength between internal waves and water upwelling around the world,a new method of quantitatively determining the relative contribution to mixing by the internal waves and water upwelling was proposed to calculate the contribution rates of the internal waves under various conditions.The potassium permanganate solution was used as tracer to observe the waveform and propagation law of the internal waves induced by aeration in laboratory.Under water depth of 1 m,temperature gradients of 0.235~0.4?/cm?aeration flow rats of 62.5~125 L/(h·m3),internal waves could not be induced 10 cm away from the aerator because of the upwelling,while stable internal waves could be generated 50 cm away from the aerator causing by the constant disturbance from aeration.The amplitude and energy of internal waves decreased as the waves traveled horizontally,The generated internal waves were overlaid with newly-generated ones,the formation of stable internal waves is the result of superposition of energy in the direction of propagation.The ranges of amplitude of internal waves induced by aeration were 2~5cm,the periods were 40~70s,and the wave velocities were 0.01~0.02m/s.The waveform of internal waves is similar to that of simple harmonic waves in the propagation process.At the same conditions of temperature gradient,thickness of the thermocline and aerator outlet position,when the aeration flow rate increased from 62.5L/(h·m3)to 125L/(h·m3),the contribution rate of the internal waves to the artificial mixing dropped from 82% to 50%.At the same conditions of temperature gradient,aeration rate and aerator outlet position,with the increase of thermocline thickness,the contribution rate of the internal waves to the artificial mixing increased from 78.5% to 83.5%.Compared with the case without the wave dissipation device,the effective power rates for mixing were increased by more than 40%.When the initial temperature gradients were 0.235?/cm,0.28?/cm and 0.4?/cm,the temperature gradient had little effect on A/T,energy density,wave energy and other parameters of internal waves.The effective power rate of water mixing gradually increased with the temperature gradient.Experimental results indicate that A/T is the most fundamental factor which influences the mixing by the internal waves,the internal waves could induce strong mixing with very little energy input,but on the contrary,water upwelling induced by aeration could induce weak mixing with high enormous energy input,namely the mixing by internal waves were more efficient in energy consumption.There are broad prospects of applying the internal waves to destroy stratification and to improve water quality in stratified source water reservoirs.