Transducer Design And Experimental Study Based On Ultrasonic Reactor For Food Waste Pretreatment

Anaerobic fermentation of kitchen waste is a process that involves microbial decomposition and transformation of kitchen waste under anaerobic conditions.To accelerate the process of anaerobic fermentation,reaction can be accelerated through pre-treatment techniques.Ultrasonic waves can generate cavitation,effectively destroying the cell structure in kitchen waste,increasing the leaching of organic matter,reducing particle size,and making it more easily decomposed and transformed by microorganisms.This study numerically simulates the motion of individual cavitation bubbles to investigate the effects of ultrasonic parameters,medium properties,and initial cavitation bubble radius on bubble wall motion.The numerical simulation results indicate that the cavitation bubble radius varies more significantly when the ultrasonic power is 100 W and the ultrasonic frequency is 28 k Hz.Higher ultrasonic power and lower ultrasonic frequency result in better cavitation effects.The density and viscosity of the medium also affect the cavitation effect of the bubbles.When the density of the medium is 0.8×103 kg/m~3 and the viscosity is 0.1 m Pa·s,the movement of the cavitation bubbles becomes more intense.Higher density hinders the formation of cavitation.Increased viscosity impedes the transfer of ultrasonic energy and also hampers cavitation formation.Simulation results with different initial cavitation bubble radii demonstrate that the strongest cavitation effect occurs when the bubble radius is around105 um at an ultrasonic frequency of 28 k Hz.Experimental verification showed that the highest aluminum foil corrosion rate was 12.8%at an ultrasonic power of 100 W,indicating the maximum cavitation intensity.This article discusses the different installation methods of single transducer and dual transducers on the ultrasonic reactor.According to the simulation results,when the single transducer is installed on the bottom surface,the cavitation ratio reaches a maximum of 17.6%.Experimental verification showed that under the condition of a single transducer,the best ultrasonic pretreatment effect is achieved when the transducer is installed on the largest radiating surface.Kitchen waste organic slurry subjected to ultrasonic excitation on the bottom surface exhibited the lowest average particle size(10.39μm)and dissolved oxygen(DO)value(9.2 mg/L).When the dual transducers are installed on the front and bottom surfaces,the average sound pressure and cavitation ratio reach their highest values,which are 1.05×10~5 Pa and 22.5%,respectively.The results of acoustic field simulation indicate that installing a single transducer on a larger radiating surface effectively enhances the cavitation effect of the reactor.When using two transducers,the optimal combination is to place them at different center points and both install on larger radiating surfaces.If the dual transducers are placed on the same surface,the distance between the centers of the transducers needs to be reduced to achieve a larger cavitation effect..The effects of ultrasonic cavitation on anaerobic fermentation of kitchen waste were investigated through experiments.After a ultrasonic treatment time of 20 minutes,there was almost no further change in the particle size and dissolved oxygen(DO)value of the kitchen waste organic slurry,while the soluble chemical oxygen demand(SCOD)increased by nearly twofold.The research results indicate that appropriately increasing the ultrasonic treatment time can effectively enhance the hydrolysis degree of organic matter in kitchen waste,but the effect becomes limited with further increase in treatment time.The use of ultrasonic pretreatment significantly improves the hydrolysis efficiency of soluble proteins.The experimental results from response surface analysis indicate that ultrasonic treatment time is the most significant influencing factor,and there is also a strong interaction among the three independent variables.Based on the analysis results,the optimal ultrasonic pretreatment conditions were determined as follows:ultrasonic treatment time of 25 minutes,ultrasonic power of 107 W/L,and ultrasonic temperature of 44°C.This paper clarifies the effects of ultrasonic parameters and medium properties on ultrasonic cavitation,systematically investigates the effects of transducer distribution mode on the cavitation intensity of the reactor,and discusses the effects of ultrasonic pretreatment on anaerobic fermentation of food waste,and the research results can provide a reference for the ultrasonic pretreatment technology of anaerobic fermentation of food waste.