Pilot Study On Destratification By Aeration-induced Internal Wave In A Reservoir

As the development of social economy, urban population becomes more and more,in order to meet the increase of water requirement demand, the reservoir is graduallybecome the main source of water supply. Aiming at the present situation of stratifiedreservoir pollution， and the common problem of conventional destratificationtechnologies such as high energy consumption and low efficiency, we propose a newmethod which is the aeration induced internal waves, and make full use of the hugeenergy potential of internal waves in the water to destroy existing stratification, toachieve the goal of high efficiency, energy saving. A pilot model reservoir with athermal structure evolved from the natural convection was designed and constructed,the feasibility of develop internal waves induced by aeration was explored, the processefficiency of destratification by internal waves were analyzed as well. This research willuse isothermal layer aeration induce wave mixing technology to improve the waterquality of a stratified water reservoirs cost-effectively and provide a theoretical basisand direct support of scientific theories.The main content of this paper are as follows:（1）Developed a pilot model reservoir to simulate the temperature stratificationbased on the natural, using cooling system of air conditioning condenser constituted tocooling bottom waters, achieved with the actual reservoir water temperaturestratification structure based on similar natural convection. Under different roomtemperature conditions, the formation temperature stratification is stable. And it has the same horizontal plane uniform temperature, cooling speed, low power consumption,simple devices and so on.（2）According to the external perturbations of two different density interface cangenerate internal waves conclusions, periodic outflow from the water-lifting aeratorcould act as a disturbing source and could be used to generate internal waves instratified water environments. Using50、75、100、125、150、175、200L/h as theexperimental tests data to be aeration conditions, the feasibility of developing internalwaves induced by aeration was explored, and the process of destratification by internalwaves were analyzed. When the air flowrates were about100L/h, relatively regularinternal waves can be developed, the wave period was similar to the period of air piston,and wave length and wave height were relatively big.（3）The position of the aerator outlet was found to affect the formation of internalwaves. When the aerator outlet was located in the top layer of the hypolimnion, betweenthe hypolimnion and thermocline boundaries, aeration can induce the formation ofinternal waves; when the aerator outlet was located in epilimnion, aeration cannotinduce the formation of internal waves. The destratification process was mainlycharacterized by reducing the temperature difference between the epilimnion andhypolimnion, by impelling the thermocline downwards and thinning the hypolimnion，the speed of destratification by internal waves increased with the air flowrate.（4）In the test, distance aerator export at different distances from the verticaltemperature profile at the same time difference, described the internal waves have widecoverage,destroy the stratification effect is relatively uniform.（5）Compared with the conventional destratification by circulated flow, in thehypolimnion water temperature is5℃, temperature gradient of thermocline is about0.565-0.410℃/cm and the hypolimnion water temperature is10℃, temperature gradientof thermocline is about0.327-0.265℃/cm conditions, when the air flowrate wasincreased from50L/h to200L/h, the efficiencies of destratification by internal wavescould be increased by25.0%～40.0%and41.2%～60.0%, respectively.