Mechanisms Of Enhanced Plant Permeation By Ultrasound And Process Optimization

Ultrasound,as a form of energy,can cause cavitation,mechanical and thermal effects in liquid media.These effects have shown very broad prospects in basic research and application technology of physics,chemistry,biology and medicine.The application of ultrasound in botanical fields such as plant straw fermentation and extraction of active substances from plant medicines is a new hotspot in the application of ultrasound in recent years.Standing wave,which is easily produced by single-frequency ultrasound propagation in the medium,makes the energy uneven and reduces the effect of ultrasound irradiation.In order to solve this problem,the mechanism of dual-frequency ultrasound propagation in medium was studied,and the influence of dual-frequency ultrasound and its parameters on cavitation was investigated,and the reason why dual-frequency ultrasound has higher energy effect was explained.Based on the study of the mechanism of dual-frequency ultrasound,a new technology of corn straw fermentation by dual-frequency ultrasound combined with alkali was put forward,and the technological parameters were optimized.Aiming at the problem of small sample size,the virtual sample generation technology based on experimental design was studied,which enlarged the application scope of the virtual sample generation technology.The main contents of this paper are as follows:(1)Dynamic study of dual-frequency ultrasonic cavitation.In this paper,the mechanism of ultrasound-enhanced infiltration was analyzed,and ultrasonic cavitation as the active mechanism of ultrasound was studied.The acoustic field under dual-frequency ultrasound was studied and the acoustic field was modeled.The dynamic model of cavitation bubble under this acoustic field was investigated.Cavitation bubble radius was simulated numerically under the action of single-frequency and dual-frequency ultrasound.The simulation results showed that the cavitation effect of dual-frequency ultrasound was stronger than that of single-frequency ultrasound.Under the same sound intensity,the cavitation effect of dual-frequency ultrasound is four times that of single-frequency ultrasound,so the energy efficiency of dual-frequency ultrasound is higher.The effects of dual-frequency ultrasound parameters such as acoustic pressure amplitude,frequency,frequency difference and initial radius of cavitation bubble on cavitation was analyzed.The design of dual-frequency ultrasound device was guided by theoretical analysis.(2)Pretreatment of corn straw by dual-frequency ultrasound combined with alkali.In order to solve the problems of standing wave generated by single-frequency ultrasound propagation in the medium and the uneven energy of ultrasound,a pretreatment process of corn straw using dual-frequency ultrasound combined with alkali was proposed.Compared with single-frequency ultrasound combined with alkali pretreatment,alkali pretreatment and untreated corn straw,dual-frequency ultrasound combined with alkali pretreatment was superior to the above three methods in the micro-structure,cumulative biogas yield,gas production rate and net energy.(3)Orthogonal experimental design(OED)and least squares support vector machine(LS-SVM)were combined to optimize the process parameters of anaerobic fermentation.In order to improve the gas production and gas production efficiency of anaerobic fermentation of corn straw,a model of cumulative gas production was established by combining OED with LS-SVM,and the parameters were optimized by using the model.The weight of corn straw,duration of ultrasound,alkali pretreatment time(2%NaOH)and single/dual frequency ultrasound were selected as the experimental factors for OED.LS-SVM combined with OED were used to establish the prediction model between cumulative gas production and pretreatment process parameters.The model was used to analyze the influence of each factor on gas production and the constraints of each factor.The genetic algorithm was used to optimize the optimal pretreatment process parameters of anaerobic fermentation biogas production.Under these parameters,the experiment validated the effectiveness of the method.(4)Virtual sample generation based on experimental design.Adding virtual samples to small sample training set can improve the machine learning ability of the sample set and solve the problem of small sample.However,virtual samples are usually generated according to prior knowledge,which limits the adaptability of virtual samples.To solve the problem of low adaptability of existing methods for generating virtual samples,a method of generating virtual samples by full factor diffusion based on experimental design was proposed.The applicability of this method was the same as that of the experimental design method,which effectively enlarged the application scope of the virtual sample generation method.The effectiveness of this method in improving the accuracy of modeling was proved by the literature data.(5)Process parameters optimization of dual-frequency ultrasound extraction based on virtual samples generated by response surface methodology(BBD-RSM).The extraction of chlorogenic acid and Luteolin from honeysuckle by dual-frequency ultrasound was studied.The experimental factors and levels of BBD-RSM were determined according to single factor experiments.The experiment was designed according to BBD-RSM and the test samples were obtained.According to the design results,the virtual samples were generated by all-factor diffusion.The virtual samples and the test samples together constitute the synthetic samples.LS-SVM was used to establish the prediction model of extraction rate for synthetic samples,and the model was used to analyze the influence of various factors on extraction rate and the relationship between them,and the optimal constraints were obtained..The improved adaptive particle swarm optimization algorithm was used to optimize the model under constraints,and the highest prediction extraction rate and the best process parameters were obtained.The experimental results showed that a higher extraction rate can be obtained under this parameter.