本文選題：高壓脈沖電場 + 數(shù)值模擬　； 參考：《浙江大學(xué)》2013年博士論文

【摘要】：液態(tài)食品的安全問題歷來就受到人們的廣泛關(guān)注,無論新鮮果蔬汁還是奶制品,甚至是酒精飲品,其產(chǎn)品的品質(zhì)和安全很大程度上取決于殺菌工序是否可靠。傳統(tǒng)的熱力殺菌方法在導(dǎo)致微生物失活的過程中,食品受熱會發(fā)生物理和化學(xué)性質(zhì)的變化,使其色、香、味、組織結(jié)構(gòu)發(fā)生改變,營養(yǎng)價(jià)值下降,產(chǎn)生各種反應(yīng),甚至檢測出有毒物質(zhì),不僅降低了產(chǎn)品的新鮮度,還嚴(yán)重影響了食品的質(zhì)量。高壓脈沖電場(Pulsed electric field,PEF)技術(shù)作為最近幾年研究最為熱門的非熱加工技術(shù)之一,不但具有良好的殺菌、鈍酶效果,還能最大限度地保持食品的新鮮度,處理過程時(shí)間短、溫度低,能量消耗少。因而,該技術(shù)以其優(yōu)良的處理效果和低廉的運(yùn)行費(fèi)用在液態(tài)食品加工領(lǐng)域展示了誘人的應(yīng)用前景。 本文綜合利用數(shù)值模擬技術(shù)、計(jì)算流體動(dòng)力學(xué)、微生物計(jì)量學(xué)、化學(xué)計(jì)量學(xué)和熒光光纖傳感技術(shù)等諸多領(lǐng)域的知識,研究高壓脈沖電場處理室結(jié)構(gòu)參數(shù)和處理過程工作參數(shù)對于高壓脈沖電場技術(shù)用于食品中微生物滅活作用的影響。通過建立不同結(jié)構(gòu)的高壓脈沖電場殺菌處理室的多物理場耦合模型,分析處理室結(jié)構(gòu)參數(shù)對于內(nèi)部物理場分布規(guī)律的影響；研究處理介質(zhì)的流量和初始溫度對于準(zhǔn)方波脈沖波形的影響,探索微生物形態(tài)特性對于微生物跨膜電勢的影響,通過建立殺菌動(dòng)力學(xué)模型分析處理過程工作參數(shù)對高壓脈沖電場技術(shù)處理效率的影響,并通過多物理場耦合模型和殺菌動(dòng)力學(xué)模型的融合,構(gòu)建基于處理室結(jié)構(gòu)參數(shù)和處理過程工作參數(shù)的高壓脈沖電場技術(shù)對微生物作用的定量預(yù)測模型,為優(yōu)化處理室結(jié)構(gòu)參數(shù)和優(yōu)選處理工作參數(shù)提供理論依據(jù),為研發(fā)具有自主知識產(chǎn)權(quán)的工業(yè)化大規(guī)模高壓脈沖電場處理系統(tǒng)提供方法依據(jù),為高壓脈沖電場處理技術(shù)的推廣應(yīng)用提供一種新的思路,對于提高處理效率和降低生產(chǎn)成本具有深遠(yuǎn)的現(xiàn)實(shí)意義。 主要研究內(nèi)容、結(jié)果和結(jié)論如下： (1)分析了不同處理室結(jié)構(gòu)對高壓脈沖電場處理室內(nèi)部物理場分布規(guī)律的影響。采用數(shù)值模擬方法構(gòu)建了高壓脈沖電場處理室的多物理場耦合仿真模型,結(jié)果表明：1)平行板型靜態(tài)處理室中電場強(qiáng)度處處相等,溫度隨處理時(shí)間上升很快。2)同軸型連續(xù)式處理室中,電場分布呈現(xiàn)不均勻性,電極間距越小,其電場分布均勻性越好。溫度隨著軸向距離的增加呈現(xiàn)線性升高,在徑向方向上,溫度的波動(dòng)較小。湍流動(dòng)能隨著液體流動(dòng)方向的軸向距離的增加而減弱,隨著電極間距的增加而減弱。3)共場型連續(xù)式處理室中,相對電場強(qiáng)度和相對能量輸入變化趨勢一致,與電極半徑和電極間距的比值(r/d)之間存在線性關(guān)系,隨著r/d值的增大而增大；共場型處理室內(nèi)部的溫度隨著物料的流動(dòng)方向逐漸升高,處理腔二的溫度比處理腔一的溫度高。在每個(gè)處理腔的出口位置,電極和絕緣材料的交界處的物料溫度顯著上升,出現(xiàn)溫度峰值。結(jié)果表明：通過建立多物理場耦合模型,可以對高壓脈沖電場處理室內(nèi)部的物理量進(jìn)行分析,得到電場強(qiáng)度、能量輸入和溫度升高與處理室結(jié)構(gòu)參數(shù)的關(guān)系。 (2)分析了層流和湍流狀態(tài)下優(yōu)化的絕緣環(huán)形狀對共場型連續(xù)式處理室內(nèi)部各物理場分布規(guī)律的影響。對三種不同絕緣環(huán)形狀(矩形內(nèi)嵌式、矩形內(nèi)嵌倒圓角式和圓弧形內(nèi)嵌式)的共場型處理室進(jìn)行仿真,結(jié)果表明：1)在層流狀態(tài)下,絕緣環(huán)的內(nèi)嵌式結(jié)構(gòu)并不能有效地改善處理室內(nèi)部的處理均勻性,反而會導(dǎo)致電場峰值和溫度峰值的產(chǎn)生。2)在湍流狀態(tài)下,改進(jìn)后的處理室中電場分布較之原結(jié)構(gòu)得到改善,峰值電場強(qiáng)度減弱,處理室徑向的流速相比于層流狀態(tài)更為均勻。湍流狀態(tài)對于處理室內(nèi)溫度控制的作用較為明顯,與原結(jié)構(gòu)相比有顯著提高。3)在兩種狀態(tài)下,相對電場強(qiáng)度和相對能量輸入的變化趨勢一致,隨著內(nèi)嵌深度和電極半徑的比值(i/r)的增大而減小,隨著電極半徑和電極間距的比值(r/d)的增大而增大。4)在兩種狀態(tài)下,相對溫升與電極間距(d)、內(nèi)嵌深度和電極半徑的比值(i/r)及電極半徑和電極間距的比值(r/d)都有關(guān)。湍流狀態(tài)下的相對溫升擬合度(0.921R20.943)優(yōu)于層流狀態(tài)。結(jié)果表明：優(yōu)化的絕緣環(huán)結(jié)構(gòu)在湍流狀態(tài)下能改善處理室內(nèi)部的物理場分布,并且通過多物理場耦合模型,得到電場強(qiáng)度、能量輸入及溫度與處理室絕緣環(huán)結(jié)構(gòu)參數(shù)之間關(guān)系。 (3)分析了處理介質(zhì)的流量和初始溫度對于準(zhǔn)方波脈沖波形的影響。結(jié)果表明：1)通過數(shù)值模擬方法得到處理介質(zhì)的電導(dǎo)率和處理室截面電流值變化趨勢一致,隨著初始溫度的升高,二者逐漸上升,而隨著處理介質(zhì)的流量增大,二者逐漸下降；而脈沖的下降時(shí)間隨著初始溫度的升高而減小,隨著處理介質(zhì)流量的增大而增大。2)建立了處理室等效電阻關(guān)于流量和初始溫度的函數(shù)關(guān)系,無論是對單個(gè)處理腔的等效電阻還是對兩個(gè)處理腔的等效并聯(lián)電阻進(jìn)行擬合,其決定系數(shù)R2均達(dá)到0.980以上,RMSE值均小于0.003。3)通過示波器和NI Labview SignalExpress軟件采集真實(shí)波形與仿真所得結(jié)果進(jìn)行比較。仿真所得的脈沖波形的下降時(shí)間與實(shí)驗(yàn)所得變化趨勢一致,但是,脈沖波形的真實(shí)下降時(shí)間大于仿真結(jié)果。結(jié)果表明：通過數(shù)值模擬方法,可以建立準(zhǔn)方波脈沖波形的下降時(shí)間與處理介質(zhì)流量和初始溫度之間的相關(guān)性。 (4)分析了不同微生物細(xì)胞的形態(tài)特性對于高壓脈沖電場技術(shù)殺菌效果的影響。1)通過數(shù)值模擬方法分析了三種微生物細(xì)胞(金黃色葡萄球菌、大腸桿菌DH5α和釀酒酵母菌)在高壓脈沖電場作用下的跨膜電勢,比較其對高強(qiáng)度電場的抵抗能力。結(jié)果表明,在同一電場強(qiáng)度下,釀酒酵母菌比大腸桿菌DH5a擁有更大的跨膜電勢,金黃色葡萄球菌的跨膜電勢最小。2)通過高壓脈沖電場技術(shù)對三種微生物殺菌實(shí)驗(yàn)表明,釀酒酵母菌對高壓脈沖電場處理過程的抵抗力最弱,大腸桿菌DH5α次之,金黃色葡萄球菌最強(qiáng),與跨膜電勢的仿真結(jié)果一致。3)較大的細(xì)胞尺寸可以增加跨膜電勢和細(xì)胞膜的電場強(qiáng)度,使細(xì)胞對于高壓脈沖電場處理更為敏感。4)不同的細(xì)胞形態(tài)對于跨膜電勢也有較大影響。桿形細(xì)胞的跨膜電勢和電場強(qiáng)度均大于擁有相同長徑和短徑的橢球形細(xì)胞。5)隨著細(xì)胞膜厚度增加,跨膜電勢增大非常微小,但是細(xì)胞膜的電場強(qiáng)度下降十分明顯。結(jié)果表明：通過數(shù)值模擬方法,可以對不同微生物的跨膜電勢進(jìn)行分析,比較不同微生物對高壓脈沖電場處理過程的抵抗力。 (5)分析了高壓脈沖電場技術(shù)的不同處理工作參數(shù)對微生物的致死規(guī)律。1)在一定范圍的處理強(qiáng)度(電場強(qiáng)度為12-21kV/cm,處理時(shí)間為30-180μs)和初始溫度(25-35℃)下,研究高壓脈沖電場技術(shù)對黃酒中釀酒酵母菌的致死作用,得到最大的殺菌效果為5.5個(gè)對數(shù)級。2)從AFM成像的結(jié)果可以看出,經(jīng)過處理后微生物細(xì)胞的數(shù)量減少,圖像呈現(xiàn)模糊的邊界,細(xì)胞邊緣塌陷,表明高壓脈沖電場技術(shù)引起了酵母菌細(xì)胞膜的破壞。3)采用Log-linear模型、Weibull模型和多元回歸模型分別對實(shí)驗(yàn)數(shù)據(jù)進(jìn)行擬合,通過另一組獨(dú)立實(shí)驗(yàn)分別對根據(jù)模型預(yù)測得到的殺菌數(shù)量和5-D值進(jìn)行驗(yàn)證,對于殺菌數(shù)量的預(yù)測,Weibull模型的Af和Bf值分別為1.082和1.019,多元回歸模型的Af和Bf值分別為1.152和0.961。對于5-D值的預(yù)測,Weibull模型的Af和Bf值分別為1.169和0.996,Log-linear模型的Af和Bf值分別為1.773和1.773。結(jié)果表明,Weibull模型和多元回歸模型都可用于預(yù)測高壓脈沖電場技術(shù)對黃酒中釀酒酵母的殺菌效果。 (7)探索了將多物理場耦合模型和殺菌動(dòng)力學(xué)模型相結(jié)合,構(gòu)建基于處理室結(jié)構(gòu)參數(shù)和處理過程工作參數(shù)的高壓脈沖電場技術(shù)的殺菌效果預(yù)測模型的可行性。結(jié)果表明：將殺菌物理場和前文所述的多物理場相結(jié)合,得到殺菌效果的預(yù)測模型,所得到的結(jié)果與真實(shí)測量所得到的酵母菌的存活數(shù)量基本一致。通過所構(gòu)建的殺菌效果預(yù)測模型,提出針對處理室結(jié)構(gòu)參數(shù)和處理過程工作參數(shù)的優(yōu)化方法。結(jié)果表明：構(gòu)建基于處理室結(jié)構(gòu)參數(shù)和處理過程工作參數(shù)的高壓脈沖電場技術(shù)的殺菌效果預(yù)測模型是可行的。
[Abstract]:The safety of liquid food has always been widely concerned. Whether fresh fruit, vegetable, dairy, or even alcoholic beverages, the quality and safety of their products depend largely on the reliability of the sterilization process. The change in nature makes its color, fragrance, taste, structure and structure change, the value of nutrition is reduced, the reaction is produced, and even the toxic substances are detected, which not only reduces the freshness of the products, but also seriously affects the quality of food. The high voltage pulsed electric field (Pulsed electric field, PEF) technology is the most popular non hot processing technology in recent years. One of the techniques, not only has good sterilization, blunt enzyme effect, but also maintains the freshness of food, the processing time is short, the temperature is low, and the energy consumption is low. Therefore, the technology shows the attractive application prospect in the field of liquid food processing with its good treatment effect and low operating cost.
In this paper, the numerical simulation technology is used to calculate the knowledge of fluid dynamics, microbiometrics, chemometrics and fluorescent fiber sensing technology. The effects of the structure parameters and processing parameters of the high voltage pulsed electric field on the inactivation of microbes in food are studied. The multi physical field coupling model of a high voltage pulsed electric field with different structures was established. The influence of the structure parameters on the distribution of the internal physical field was analyzed. The influence of the flow rate and initial temperature of the medium on the quasi square wave pulse waveform was studied, and the influence of the microbiological characteristics on the transmembrane potential of the microorganism was explored. By establishing a germicidal kinetic model to analyze the effect of the working parameters of the processing process on the efficiency of the high voltage pulsed electric field, and through the fusion of the multi physical field coupling model and the germicidal kinetic model, the quantitative prediction of the action of the high pressure pulse electric field based on the structure parameters of the processing chamber and the working parameters of the processing process is constructed. The model provides a theoretical basis for optimizing the structural parameters of the processing chamber and optimizing the processing parameters. It provides a basis for the research and development of the industrial large-scale high voltage pulsed electric field processing system with independent intellectual property rights. It provides a new idea for the popularization and application of high voltage pulsed electric field processing technology, which can improve the processing efficiency and reduce production. The cost has far-reaching practical significance.
The main research contents, results and conclusions are as follows:
(1) the influence of different processing chamber structure on the physical field distribution of high voltage pulsed electric field is analyzed. A multi physical field coupling simulation model of high voltage pulsed electric field processing room is constructed by numerical simulation. The results show that 1) the electric field intensity in the parallel plate static processing chamber is all equal and the temperature rises rapidly with the processing time. .2) the distribution of electric field appears inhomogeneous in a coaxial continuous processing chamber. The smaller the distance of the electrode is, the better the distribution of the electric field is better. The temperature increases linearly with the increase of the axial distance. In the radial direction, the fluctuation of the temperature is smaller. The turbulent kinetic energy decreases with the increase of the axial distance of the liquid flow direction, with the electrode spacing. In the continuous treatment chamber, the relative electric field intensity and the relative energy input change in the continuous treatment chamber, and there is a linear relationship between the ratio of the electrode radius and the ratio of the electrode distance (r/d), which increases with the increase of the r/d value; the temperature of the common field treatment increases with the flow direction of the material, and the treatment cavity is two. The temperature of the cavity is higher than that of the cavity. At the exit position of each processing chamber, the temperature of the material at the junction of the electrode and the insulating material rises significantly, and the temperature peak appears. The results show that the physical and physical amount of the electric field can be analyzed, the intensity of the electric field and the input of the energy can be obtained by the establishment of a multi physical field coupling model. And the relationship between the temperature increase and the structure parameters of the treatment room.
(2) the influence of the shape of the insulated ring under laminar and turbulent flow on the distribution of the physical fields in the interior of the chamber is analyzed. The simulation of the common field processing chamber of three different insulation ring shapes (rectangle inlay, rectangle and arc inlay) is carried out. The results show that 1) in the laminar flow state, the insulation is insulated. The embedded structure of the ring can not effectively improve the treatment uniformity in the treatment of the interior. Instead, it will lead to the generation of the peak and temperature peak of the electric field.2). In the turbulent state, the electric field distribution in the improved treatment room is better than the original structure, the peak electric field intensity is weakened, and the flow velocity in the chamber is more uniform than that of the laminar flow. The effect of the turbulent state on the temperature control is more obvious. Compared with the original structure, it has a significant increase of.3). In the two states, the relative electric field intensity and the relative energy input are in the same trend. With the increase of the ratio of the embedded depth and the radius of the electrode (i/r), the ratio of the electrode radius to the electrode spacing (r/d) increases. In two states, the relative temperature rise and the electrode spacing (d), the ratio of the embedded depth to the electrode radius (i/r) and the ratio of the electrode radius to the electrode spacing (r/d) are all related. The relative temperature rise fitting (0.921R20.943) in the turbulent state (0.921R20.943) is superior to the laminar flow state. The results show that the optimized insulation ring structure can be improved in the turbulent state. The physical field distribution in the interior is dealt with, and the relationship between the electric field strength, the energy input and the temperature of the insulation ring of the treatment chamber is obtained through the multi physical field coupling model.
(3) the influence of the flow rate and initial temperature of the medium on the quasi square wave pulse waveform is analyzed. The results show that: 1) the conductivity of the medium is obtained by the numerical simulation method and the current value of the section of the treatment chamber is the same. With the increase of the initial temperature, the two gradually rises, and with the increase of the flow rate of the treatment medium, the two are gradually increasing. The drop time of the pulse decreases with the increase of the initial temperature. With the increase of the flow rate of the treatment medium, the function of the equivalent resistance of the processing chamber is established on the flow and the initial temperature, which is determined by the equivalent resistance of the single processing chamber or the equivalent resistance of the two lumen. The coefficient R2 is above 0.980 and the RMSE value is less than 0.003.3). The actual waveform obtained by the oscillograph and the NI Labview SignalExpress software is compared with the simulation results. The simulation results are in accordance with the experimental results, but the real descent time of the pulse wave shape is larger than the simulation result. Ming: through numerical simulation, we can establish the correlation between the falling time of quasi square wave pulse and the treatment of medium flow and initial temperature.
(4) the influence of the morphological characteristics of different microorganism cells on the bactericidal effect of high voltage pulsed electric field (.1) was analyzed. Through numerical simulation, the transmembrane potential of three microorganism cells (Staphylococcus aureus, Escherichia coli DH5 alpha and Saccharomyces cerevisiae) under the action of high voltage pulsed electric field was analyzed, and the resistance to high intensity electric field was compared. The results showed that the Saccharomyces cerevisiae had greater transmembrane potential than the Escherichia coli DH5a at the same electric field intensity, and the transmembrane potential of Staphylococcus aureus was least.2). The resistance of Saccharomyces cerevisiae to the treatment of high pressure pulsed electric field was the weakest by high voltage pulsed electric field technique to three microorganism sterilization experiments, and the Escherichia coli D H5 alpha, Staphylococcus aureus is the strongest, which is consistent with the simulation results of the transmembrane potential.3) the larger cell size can increase the transmembrane potential and the electric field intensity of the cell membrane, and make the cells more sensitive to the high voltage pulsed electric field treatment. The different cell morphology also has a greater influence on the transmembrane potential. The transmembrane potential and electric field of the rod shaped cells The strength of the ellipsoidal cell.5 with the same length diameter and short diameter increased with the increase of the thickness of the cell membrane. The increase of the electric potential of the membrane was very small, but the electric field intensity of the cell membrane decreased very obviously. The results showed that the transmembrane potential of different microbes could be analyzed by the numerical simulation method and the high pressure pulse was compared with the different microbes. Resistance in the process of electric field treatment.
(5) the lethal effect of high voltage pulsed electric field technology on Saccharomyces cerevisiae in yellow wine was studied under a certain range of treatment intensity (electric field intensity is 12-21kV/cm, treatment time 30-180 s) and initial temperature (25-35 degrees C), and the maximum sterilization was obtained. The effect is 5.5 logarithmic level.2) from the results of AFM imaging, it can be seen that after processing, the number of microorganism cells is reduced, the image presents a fuzzy boundary, the edge of the cell collapses, indicating that the high voltage pulsed electric field technique causes the destruction of the yeast cell membrane.3) using the Log-linear model, the Weibull model and the multiple regression model respectively. According to the fitting, the number of bactericidal and 5-D values predicted by the model were verified by another group of independent experiments. The Af and Bf values of the Weibull model were 1.082 and 1.019 respectively. The Af and Bf values of the multiple regression models were 1.152 and 0.961., respectively, and the Af and Bf values of the Weibull model respectively. For 1.169 and 0.996, the Af and Bf values of the Log-linear model are 1.773 and 1.773. respectively. The Weibull model and multiple regression model can be used to predict the bactericidal effect of high voltage pulsed electric field technology on the Saccharomyces cerevisiae in yellow wine.
(7) the feasibility of combining the multi physical field coupling model with the germicidal kinetic model is explored to construct the bactericidal effect prediction model of the high voltage pulsed electric field based on the structure parameters of the processing chamber and the working parameters of the processing process. The results show that the bactericidal physical field and the multi physical field described in the previous article are combined to obtain the pre sterilization effect. The results obtained are in accordance with the survival number of the yeast obtained by the real measurement. The optimization method for the structure parameters of the treatment room and the working parameters of the processing process is proposed through the prediction model of the bactericidal effect. The results show that the high pressure pulse based on the parameters of the processing chamber structure and the processing parameters of the process is constructed. It is feasible to predict the germicidal efficacy of the electric field technology.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2013
【分類號】：TS201.3

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