Simulational And Experimental Study On The Ultrasound Of Transmission Characteristics In Urban Waste Activated Sludge

When the ultrasonic cavitation effect occurring in the sludge suspension it will generate the high temperature (5000K), high pressure (50MPa) and a strong shock wave with the high-intensity shear force and bring in extreme physical environment. High-intensity shear stress can damage the structure of the sludge characteristics and to accelerate the anaerobic digestion speed of sludge subsequent treatment. Thus, ultrasonic crack sludge is a promising pretreatment method of sludge, but its high energy consumption bottleneck restricting the rapid development of the technology. In order to break the energy consumption bottleneck and to promote the ultrasonic crack sludge of technology large-scale application in China. This paper from the perspective of engineering thermophysics, using the urban concentration waste activated sludge as the research object, around the ultrasound transmission characteristics in the sludge, a serial correlation of the theoretical derivation, numerical computation, numerical simulation and experimental research have been done. The main research contents and conclusions are as follows.â‘ The ultrasonic propagation model of spherical particles of sludge has been built and derived viscosity wave absorption coefficient and thermal wave absorption coefficient, and based on the rheological properties of waste activated sludge suspensions, the viscous absorption coefficient of sludge has been deduced when ultrasound propagation in the sludge, which are the first innovation of this article.Viscous wave absorption coefficient and thermal wave absorption coefficient are both connection with the volume percentage concentration of sludge particles in the media of waste activated sludge suspensions. According to the sludge and water-related physical parameters, we can find the viscous wave absorption coefficient and thermal wave absorption coefficient. When the viscous wave length and roughly equal to the sludge particle size, the viscosity absorption loss are maximum. At low frequencies, the temperature difference between the sludge particles and the water will reach equilibrium during in the sound waves time. At high frequencies, only the surface of particles in the sludge is partly involved in the process of heat conduction. When the heat wave lengths close to the sludge floc size, the entire sludge suspended particles are involved in the heat transfer loss mechanism. The viscous absorption coefficient is relating with the sludge of plastic viscosity when ultrasonic wave propagation in the sludge, but because of the plastic viscosity changes with the sludge concentration which lead the viscous absorption coefficient has the uncertain.â‘¡According to the Engineering Thermophysics, based on the energy balance basis, the cavitation bubble energy characteristics were studied in detail by numerical calculation at the end of the first collapse. The description of the cavitation bubble collapse process is proposed in a different thermodynamic state with a different thermal physical model bubbles at the first time. During the first collapse process of cavitation bubble, the defined criteria and the location of the demarcation point of isothermal process and adiabatic process of different thermodynamic state are give out in the first time, which is the second innovation in this paper.The energy conversion characteristics of cavitation bubbles during the end of collapse are shown that the combined force power, kinetic energy, temperature, pressure, temperature difference heat transfer between inside and outside of the bubble and minimum radius values are all increased to the maximum or minimum at the same time and at the cavitation bubble collapse point. It is for the combined force power together with the kinetic energy reduced to the minimum at the cavitation bubble collapse point that provides the enough energy for the temperature difference heat transfer, temperature and pressure are all increased to the maximum and also embodies the energy transmission and conversion. Cavitation bubble is compressed to the initial radius point, which point is demarcation point between of isothermal process and adiabatic process. The point of the process before is thermodynamic isothermal process, after that point to the minimum radius value point of cavitation bubble is dynamics adiabatic process. Therefore, cavitation bubbles under different thermodynamic state using different thermalophysics models to describe the collapse process of cavitation bubbles is more suitable.â‘¢To use the numerical simulation software COMSOL Multiphysics, the propagation characteristics of sound intensity has been simulated in a variety of simulation conditions because of the propagation characteristics of sound intensity is the most representative of the energy characteristics of ultrasonic propagation in the waste activated sludge.The simulation results can provide a theoretical reference for the ultrasonic treatment sludge of sound chemical reaction container of design and optimization, which is the third innovation of this article.For cylindrical and square shape of container, the spatial distribution of sound intensity showing a similar "cylinder" shape, which shows the spatial distribution of sound intensity with a certain concentration. Ultrasonic wave emitting surface area size has a direct impact on the spatial distribution of sound intensity. Power increases only increase the overall sound intensity values of each point in the sound field. For a single probe, when the cylindrical container radius and the rectangular containers'length and width change, the sound intensity of the two containers with a similar change trend and the sound intensity spatial distribution is similar to cylinder shape. When the height is constant,with the container radius (or length and width) to reduce, the increase of cylinder height of sound intensity distribution space area is reflected in the distance increases of the attenuation of sound intensity. The high sound intensity values spatial distribution area increase gradually and farther away from the emitting surface and the sound intensity of unit distance decay rate decrease gradually. By comparison we can see, when the relevant parameters are equal or similar,for a single probe sonochemical reactor, cylindrical container is more suitable than the rectangular container for sound chemical reaction vessels, spherical container does not suitable for chemical containers. When layout of multi-probe ultrasonic transmitter, the sound intensity of the coverage area in the sound field and the effective role of ultrasound area are need to be considered.â‘£Ultrasonic sound intensity propagation characteristics in the concentration of waste activated sludge has been done by experimental study. By using the ultrasonic thermal probe method based on the principle of conservation of energy conversion, by measuring the temperature in ultrasonic field to indicate sound intensity value of ultrasound propagation in the waste activated sludge.By changing the position of ultrasound probe emitting surface, changing the ultrasonic frequency, changing the input power and the changing the ultrasonic continuing time and other ultrasonic parameters, the ultrasound propagation experiment in the waste activated sludge have been done in various experimental conditions. Experimental results indicated that, in a certain frequency and power, sound intensity near the probe in the launched surface is sharp decline, after that the trend of the sound intensity curve is relatively flat around becoming more and more certain value. This is because near the ultrasound emitting surface taking places a strong ultrasonic cavitation resulting of ultrasonic cavitation intensity values decrease very quickly.There exists an optimum power under the same frequency makes each point on the axis of the sound intensity values is up to the point of maximum. Under the other same parameters, the power is greater not must means that the sound intensity value is higher. The ultrasonic frequency and power are important to the sound intensity values and there exists a most optimal frequency and power value. With the increasing of ultrasonic continuing time, the trend of most sound intensity curves similar to the sine curve, and the all sound intensity value of the overall change trend is increasing.