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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Electrohydrodynamic Manipulation Of Liquid Droplet Emulsions In A Microfluidic Channel

Wehking, Jonathan 01 January 2013 (has links)
This work specifically aims to provide a fundamental framework, with some experimental validation, for understanding droplet emulsion dynamics in a microfluidic channel with an applied electric field. Electrification of fluids can result in several different modes of electrohydrodynamics (EHD). Several studies to date have provided theoretical, experimental, and numerical results for stationary droplet deformations and some flowing droplet configurations, but none have reported a method by which droplets of different diameters can be separated, binned and routed through the use of electric fields. It is therefore the goal of this work to fill that void and report a comprehensive understanding of how the electric field can affect flowing droplet dynamics. This work deals with two primary models used in electrohydrodynamics: the leaky dielectric model and the perfect dielectric model. The perfect dielectric model assumes that fluids with low conductivities do not react to any effects from the small amount of free charge they contain, and can be assumed as dielectrics, or electrical insulators. The leaky dielectric model suggests that even though the free charge is minimal in fluids with low conductivities, it is still is enough to affect droplet deformations. Finite element numerical results of stationary droplet deformations, implemented using the level set method, compare well both qualitatively (prolate/oblate and vortex directions), and quantitatively with results published by other researchers. Errors of less than 7.5% are found when comparing three-dimensional (3D) numerical results of this study to results predicted by the 3D leaky dielectric model, for a stationary high conductivity drop suspended in a slightly lower conductivity suspending medium. Droplet formations in a T-junction with no applied electric field are adequately predicted numerically using the level set finite element technique, as demonstrated by other researchers and verified in this study. For 3D models, droplet size is within 6%, and droplet production frequency is within 2.4% of experimental values found in the microfluidic Tjunction device. In order to reduce computational complexity, a larger scale model was solved first iii to obtain electrical potential distributions localized at the channel walls for the electrode placement configurations. Droplet deceleration and pinning is demonstrated, both experimentally and numerically, by applying steep gradients of electrical potential to the microchannel walls. As droplets flow over these electrical potential “steps,” they are pinned to the channel walls if the resulting electric forces are large enough to overcome the hydrodynamic forces. A balance between four dimensionless force ratios, the electric Euler number (Eue – ratio of inertial to electric forces), Mason number (M a – ratio of viscous to electric forces), electric pressure (P s – ratio of upstream pressure forces to electric forces), and the electric capillary number (Cae – ratio of electric to capillary forces) are used to quantify the magnitudes of each of these forces required to pin a droplet, and is consistent with a cubic dependency on the drop diameter. For larger drop diameters, effects of hydrodynamic forces become more prominent, and for smaller droplets, a greater electric forces is required due to the proximity of the droplet boundary with reference to the electrified channel wall. Droplet deceleration and pinning can be exploited to route droplets into different branches of a microfluidic T-junction. In addition, using steep electrical potential gradients placed strategically along a microchannel, droplets can even be passively binned by size into separate branches of the microfluidic device. These characteristics have been identified and demonstrated in this work.
42

Performance of EHD assisted convective boiling heat exchangers utilizing dielectric fluids

Nangle-Smith, Sarah 02 August 2018 (has links)
Electrohydrodynamics in convective boiling heat exchangers has been studied since the early 1990’s and has been shown to result in a large variation in the average performance enhancement of these systems. The behaviour of EHD assisted convective boiling heat exchangers, is still largely unpredictable owing to a number of conflicting parameters which are rarely kept constant in empirical studies, i.e. flow pattern and heat flux. In this thesis, it is hypothesised that by reducing the number of confounding variables in the experimental test conditions, and understanding the behaviour of EHD in convective boiling systems from a flow pattern dependent point of view, this can allow for the development of flow pattern dependent experimental correlations & numerical models to develop a methodology for performance prediction, control strategies and system integration for an EHD assisted convective boiling heat exchange device. A 30 cm long, smooth, concentric, annular test section is used to analyse the effect of EHD on convective boiling performance under constant flow pattern, constant, low heat flux, and negligible free charge conditions. Saturated boiling conditions for flow-rates between 60 kg/m2s and 180 kg/m2s and thermodynamic quality range of 0.25 - 0.55 were tested. Heat transfer enhancement ranged from 0.95 to 2.3 fold and pressure drop penalty varied from 1.4-3 fold over these test conditions. The local EHD behaviour was found to be more consistent along the axial length of the test section compared to empirical data in the literature, which uses much longer test section lengths, where flow pattern can vary. An experimental database of EHD convective boiling data for horizontal annular electrode geometries was compiled to be used for analysis purposes. The performance of the heat exchanger in both free-field and high voltage conditions could be explained by looking at the flow patterns in each case. Electrostatic modelling was used to determine electric field strength distributions and interfacial stress due to the dielectrophoretic and electrostriction forces on the liquid vapour interface, which induce liquid extraction based flow pattern re-distribution in two phase dielectric flows. A fully coupled 2D, adiabatic numerical model for the effect of the electric body force on two phase flow pattern distribution was developed. Charge was neglected in this model. Two different models for the interface migration were used and compared; a moving mesh (MM) interface tracking model and a volume of fluid (VOF) interface tracking mode. Both were verified against published experimental data. For the liquid extraction verification case, the VOF model suffers interface stretching up to 300% resulting in a 42% slower extraction time and underestimated forces. However, it is useful to use the VOF model when simulating complex flow patterns which are subject to topological changes like bubble detachment or droplet coalescence as these cannot be simulated with the moving mesh model. The moving mesh model can be used to determine the error in forces and phase velocities when using the VOF model. A methodology for generating two-phase EHD flow pattern maps was developed by incorporating the electric Froude number into each of the flow pattern transition equations. A semi-analytical model was developed to determine the maximum interfacial stress due to EHD for stratified flows to reduce the requirement of numerical modeling, and thus the flow pattern map generation methodology is fully equation based. Although transition equations developed by multiple researchers were used and compared, it is recommended that the Steiner transitions equations be used for EHD two-phase flow pattern mapping, until more fundamental experimental data can be gathered to modify the semi-empirical transition equations used in more state-of-the-art maps. EHD was found to significantly affect the “stratified-stratified wavy (SSW)” and “stratified wavy – intermittent/annular (SWIA)” transitions for concentric horizontal geometries, with minimal effect on the transition to dryout and no effect on the “intermittent dispersed bubbly (IB)” transition. The EHD flow pattern maps were generated and compared against data from the present study and a database of experimental EHD convective boiling studies. The regions where maximum enhancement were seen in the literature correlate well with those regions predicted by the maps. Performance correlations for the EHD convective boiling heat transfer and pressure drop were developed. They are based on the free-field Kandlikar correlation [1] for two-phase heat transfer and the Chisholm-Laird [2] correlations for two-phase pressure drop, respectively. The EHD flow pattern map is used to determine what the flow pattern for a given applied voltage will be, and flow pattern based enhancement linear multipliers are then used to determine the EHD performance above the free-field case. EHD is a form of active enhancement, i.e. it requires power. Thus, it would be used in systems that require performance control or regulation, in addition to some niche applications like space where it can be used instead of gravity. A method for EHD controller design was established and an EHD control algorithm was designed and implemented on the test section for the flow pattern and applied waveforms that were determined to be optimal to maximize enhancement in this geometry. System identification was performed empirically to determine the transfer function between EHD voltage and heat load to be controlled for. This resulted in a 1st order plus dead-time model to which proportional-integral controller constants were tuned. Two controllers were developed; a PID control system and a Smith model predictive control system and these were compared based on their ability to regulate the output quality of the heat exchanger when subject to dynamic heat loading. Regulation was achieved for a dynamic heat load within ±25% bound from the designed steady state load. These controllers operate on one flow pattern as the test section is 30 cm long. Flow pattern dependent controller design would be required for a full length convective boiling heat exchanger. / Thesis / Doctor of Philosophy (PhD) / Control of boiling heat transfer using electric fields is hard to predict. This thesis presents a set a design guidelines based on how the electric field enhances the flow pattern.
43

Aumento da eficiência de um dispositivo eletro-hidrodinâmico através da alteração das características geométricas do eletrodo ativo / Increased efficiency of an electro-hydrodynamic device by changing the geometric characteristics of the active electrode

Croce, José Antonio Garcia 31 October 2014 (has links)
Forças eletro-hidrodinâmicas apresentam boas qualidades para a utilização como meio de produzir e manipular escoamentos. Um de seus grandes méritos consiste na falta de partes móveis para a introdução de quantidade de movimento em escoamentos. Foi realizado um estudo experimental para a investigação e comparação de três diferentes configurações dos eletrodos usados para a produção de dispositivos eletro-hidrodinâmicos gerados por descarga de barreira dielétrica. Uma configuração é composta de eletrodos retangulares planos e a outra de um fio e um eletrodo retangular plano. A outra configuração usa uma nova configuração com um eletrodo plano de borda serrilhada, como eletrodo ativo, e um eletrodo retangular plano isolado. Todas as configurações foram investigados para entender o comportamento na produção de escoamento. Medições de tubo Pitot dos perfis de velocidade dos jatos de parede foram feitas em várias distâncias a partir da região da descarga elétrica. Na sequência, a medição do escoamento ao longo do eletrodo serrilhado foi realizada. Assim, pretende-se determinar as características de escoamento tridimensionais produzidas por esta configuração. Os resultados mostram melhores características da configuração serrilhado para ser utilizado na produção de escoamento mais intensos. / Electro-hydrodynamic forces have good qualities to be used to produce and manipulate flows. One of its great merits is the lack of moving parts to introduce momentum in flows. An experimental study for measure and comparing three different configurations of electrodes used for the production of electro-hydrodynamic devices generated by dielectric barrier discharge was performed. One configuration is composed of rectangular at electrodes and the other of a wire electrode and a rectangular at electrode. The other uses a new configuration with a serrated edge flat plane electrode, as the active electrode and an isolated rectangular flat. All configurations are investigated to understand the behavior in the production of the flow. Pitot tube measurements of velocity profiles of the wall jets are made at various distances away from the electrical discharge region. Further, the measurement of the flow along the serrated electrod is performed. Thus, it is intended to determine the three-dimensional flow characteristics produced by this configuration. The results show the best features of serrated configuration to be used in the production of more intense flow.
44

Modulating Electro-osmotic Flow with Polymer Coatings

Hickey, Owen 12 January 2012 (has links)
Micro- and nano-fluidic devices represent an exciting field with a wide range of possible applications. These devices, typically made of either silica or glass, ionize when placed in contact with water. Upon the application of an electric field parallel to the wall, a flow is produced by the charged walls called the electro-osmotic flow (EOF). Since electric fields are so often used as the driving force in these devices, EOF is an extremely common phenomenon. For this reason it is highly desirable to be able to control EOF in order to optimize the functioning of these devices. One method which is quite common experimentally is the modification of the surface using polymer coatings. These coatings can be either adsorbed or grafted, and charged or neutral. The first part of this thesis looks at the role of neutral adsorbed polymer coatings for the modulation of EOF. Specifically our simulation results show that for adsorbed coatings made from a dilute polymer solution the strongest quenching of EOF is found for an adsorption strength at the phase transition for adsorption of the polymers. Further evidence is presented that shows that by using a high density of polymer solution and a polymer which has a strong attraction to the surface a very thick polymer layer can be created. Next the case of charged grafted polymer coatings is examined. The variation of the EOF with respect to several key parameters which characterize the polymer coating is investigated and compared to theory. The prediction that the electrophoretic velocity of the polymers is the same as the EOF generated by a coating made up of the same polymers is found to be false though the two values are quite close. The last section presents results which show how hydrodynamic interactions in charged polymer systems can be modeled mesoscopically without the use of explicit charges by forcing a slip between monomers and the surrounding fluid. This model is validated by simulating some surprising predictions made in the literature such as an object with no net charge having a non-zero force when subjected to an electric field, and how the velocity can even be perpendicular to the applied electric field. The thesis can be roughly divided into two topics: using polymer coatings to modulate EOF, and the free solution electrophoresis of polyelectrolytes. While EOF and free solution electrophoresis might seem unrelated it will be shown that the concepts are the same in both cases. In fact while not investigated in this thesis, the mesoscopic simulation methods for electrophoresis could be applied to the modulation of EOF with polymer coatings allowing for the simulation of longer length and time scales or more complex systems such as heterogeneously grafted colloids.
45

Modulating Electro-osmotic Flow with Polymer Coatings

Hickey, Owen 12 January 2012 (has links)
Micro- and nano-fluidic devices represent an exciting field with a wide range of possible applications. These devices, typically made of either silica or glass, ionize when placed in contact with water. Upon the application of an electric field parallel to the wall, a flow is produced by the charged walls called the electro-osmotic flow (EOF). Since electric fields are so often used as the driving force in these devices, EOF is an extremely common phenomenon. For this reason it is highly desirable to be able to control EOF in order to optimize the functioning of these devices. One method which is quite common experimentally is the modification of the surface using polymer coatings. These coatings can be either adsorbed or grafted, and charged or neutral. The first part of this thesis looks at the role of neutral adsorbed polymer coatings for the modulation of EOF. Specifically our simulation results show that for adsorbed coatings made from a dilute polymer solution the strongest quenching of EOF is found for an adsorption strength at the phase transition for adsorption of the polymers. Further evidence is presented that shows that by using a high density of polymer solution and a polymer which has a strong attraction to the surface a very thick polymer layer can be created. Next the case of charged grafted polymer coatings is examined. The variation of the EOF with respect to several key parameters which characterize the polymer coating is investigated and compared to theory. The prediction that the electrophoretic velocity of the polymers is the same as the EOF generated by a coating made up of the same polymers is found to be false though the two values are quite close. The last section presents results which show how hydrodynamic interactions in charged polymer systems can be modeled mesoscopically without the use of explicit charges by forcing a slip between monomers and the surrounding fluid. This model is validated by simulating some surprising predictions made in the literature such as an object with no net charge having a non-zero force when subjected to an electric field, and how the velocity can even be perpendicular to the applied electric field. The thesis can be roughly divided into two topics: using polymer coatings to modulate EOF, and the free solution electrophoresis of polyelectrolytes. While EOF and free solution electrophoresis might seem unrelated it will be shown that the concepts are the same in both cases. In fact while not investigated in this thesis, the mesoscopic simulation methods for electrophoresis could be applied to the modulation of EOF with polymer coatings allowing for the simulation of longer length and time scales or more complex systems such as heterogeneously grafted colloids.
46

Modulating Electro-osmotic Flow with Polymer Coatings

Hickey, Owen 12 January 2012 (has links)
Micro- and nano-fluidic devices represent an exciting field with a wide range of possible applications. These devices, typically made of either silica or glass, ionize when placed in contact with water. Upon the application of an electric field parallel to the wall, a flow is produced by the charged walls called the electro-osmotic flow (EOF). Since electric fields are so often used as the driving force in these devices, EOF is an extremely common phenomenon. For this reason it is highly desirable to be able to control EOF in order to optimize the functioning of these devices. One method which is quite common experimentally is the modification of the surface using polymer coatings. These coatings can be either adsorbed or grafted, and charged or neutral. The first part of this thesis looks at the role of neutral adsorbed polymer coatings for the modulation of EOF. Specifically our simulation results show that for adsorbed coatings made from a dilute polymer solution the strongest quenching of EOF is found for an adsorption strength at the phase transition for adsorption of the polymers. Further evidence is presented that shows that by using a high density of polymer solution and a polymer which has a strong attraction to the surface a very thick polymer layer can be created. Next the case of charged grafted polymer coatings is examined. The variation of the EOF with respect to several key parameters which characterize the polymer coating is investigated and compared to theory. The prediction that the electrophoretic velocity of the polymers is the same as the EOF generated by a coating made up of the same polymers is found to be false though the two values are quite close. The last section presents results which show how hydrodynamic interactions in charged polymer systems can be modeled mesoscopically without the use of explicit charges by forcing a slip between monomers and the surrounding fluid. This model is validated by simulating some surprising predictions made in the literature such as an object with no net charge having a non-zero force when subjected to an electric field, and how the velocity can even be perpendicular to the applied electric field. The thesis can be roughly divided into two topics: using polymer coatings to modulate EOF, and the free solution electrophoresis of polyelectrolytes. While EOF and free solution electrophoresis might seem unrelated it will be shown that the concepts are the same in both cases. In fact while not investigated in this thesis, the mesoscopic simulation methods for electrophoresis could be applied to the modulation of EOF with polymer coatings allowing for the simulation of longer length and time scales or more complex systems such as heterogeneously grafted colloids.
47

Aumento da eficiência de um dispositivo eletro-hidrodinâmico através da alteração das características geométricas do eletrodo ativo / Increased efficiency of an electro-hydrodynamic device by changing the geometric characteristics of the active electrode

José Antonio Garcia Croce 31 October 2014 (has links)
Forças eletro-hidrodinâmicas apresentam boas qualidades para a utilização como meio de produzir e manipular escoamentos. Um de seus grandes méritos consiste na falta de partes móveis para a introdução de quantidade de movimento em escoamentos. Foi realizado um estudo experimental para a investigação e comparação de três diferentes configurações dos eletrodos usados para a produção de dispositivos eletro-hidrodinâmicos gerados por descarga de barreira dielétrica. Uma configuração é composta de eletrodos retangulares planos e a outra de um fio e um eletrodo retangular plano. A outra configuração usa uma nova configuração com um eletrodo plano de borda serrilhada, como eletrodo ativo, e um eletrodo retangular plano isolado. Todas as configurações foram investigados para entender o comportamento na produção de escoamento. Medições de tubo Pitot dos perfis de velocidade dos jatos de parede foram feitas em várias distâncias a partir da região da descarga elétrica. Na sequência, a medição do escoamento ao longo do eletrodo serrilhado foi realizada. Assim, pretende-se determinar as características de escoamento tridimensionais produzidas por esta configuração. Os resultados mostram melhores características da configuração serrilhado para ser utilizado na produção de escoamento mais intensos. / Electro-hydrodynamic forces have good qualities to be used to produce and manipulate flows. One of its great merits is the lack of moving parts to introduce momentum in flows. An experimental study for measure and comparing three different configurations of electrodes used for the production of electro-hydrodynamic devices generated by dielectric barrier discharge was performed. One configuration is composed of rectangular at electrodes and the other of a wire electrode and a rectangular at electrode. The other uses a new configuration with a serrated edge flat plane electrode, as the active electrode and an isolated rectangular flat. All configurations are investigated to understand the behavior in the production of the flow. Pitot tube measurements of velocity profiles of the wall jets are made at various distances away from the electrical discharge region. Further, the measurement of the flow along the serrated electrod is performed. Thus, it is intended to determine the three-dimensional flow characteristics produced by this configuration. The results show the best features of serrated configuration to be used in the production of more intense flow.
48

Étude des panaches électrohydrodynamiques plans / Study of electrohydrodynamic plane plumes

Yan, Zelu 18 September 2014 (has links)
Ce travail est une analyse de la structure des panaches Électrohydrodynamiques plans également appelés jets Électrohydrodynamiques en géométrie plane. Il a pour objectif de proposer une description la plus précise possible de l'écoulement, d'apporter une meilleure compréhension des phénomènes physiques notamment à l'aide de modèles simples et de quantifier la force électrique. Le chapitre I est une étude bibliographique qui propose un résumé des principales connaissances sur la structure de deux écoulements très similaires aux jets EHD : les jets classiques et les panaches thermiques. Le chapitre II est consacré à la présentation du montage expérimental, ainsi qu'à la méthodologie expérimentale utilisée dans cette étude. La qualité des mesures obtenues grâce à la méthode de vélocimétrie par images de particule y est discutée ; les problèmes de non corrélation, de convergence statistique des résultats y sont par exemple abordés. L'analyse des champs de vitesse permet de mettre en évidence la structure des panaches et de proposer une classification des jets EHD. Le chapitre III est consacré à l'étude de la force électrique dans les panaches EHD. L'actionneur utilisé pour produire le jet plan est de type lame-plan. Trois méthodes indirectes ont été utilisées pour estimer la force à partir du champ de vitesse. La première méthode appelée méthode intégrale classique calcule la force par intégration volumique de l'équation de Navier-Stokes. La deuxième méthode appelée méthode RANS intégrale estime la force à partir de chacun des termes de l'équation RANS en utilisant une décomposition de la vitesse en valeur moyenne et fluctuation. Enfin, la force est également calculée selon une troisième méthode basée sur une modélisation simplifiée de l'écoulement inspirée des travaux de Malraison et Atten. Dans le dernier chapitre, l'étude est étendue à un écoulement électroconvectif de type jet de paroi électrique. Il est généré par un actionneur à barrière diélectrique. L'étude est faite avec deux types des liquides diélectriques différents. Comme pour le jet plan, l'analyse des champs de vitesse permet de définir les structures de l'écoulement mais également de calculer l'intensité de la force produite. / This work is related to the analysis of the structure of electrohydrodynamic plane plumes also called electrohydrodynamic jets in plane geometry. The aim of this work is to provide a more precise description and a better understanding of its physical phenomenon and to quantify the electric force using the simple models. Chapter I is a literature review which provides a summary of two flows with the structure very similar to EHD jets: classic jets and thermal plumes. Chapter II is devoted to the presentation of the experimental setup and method used in this study. The quality of the measurements obtained by the method of Particle Image Velocimetry is discussed; problems of non correlation and statistical convergence of the results are also discussed. The analysis of velocity fields allows us to identify the structure and propose a classification of the EHD plumes. Chapter III is devoted to the study of the electric force in the EHD plumes. The actuator used to produce the plane jet is a blade plane device. Three indirect methods were used to estimate the force from the velocity field. The first classical method called integral method calculates the force by volumetric integration of Navier-Stokes equations. The second method called RANS integral method estimates the force from each term of RANS equation using the average and fluctuating velocity components. Finally, the force is also calculated using a third approach with a simplified flow model based on the work of Malraison and Atten. In the last chapter, the study is extended to one type of électroconvectif flow: the electrical wall jet. It is generated by a dielectric barrier actuator. The study is carried out with two different dielectric liquids. As is the case with plane jet, the analysis of velocity fields is used to define the flow structures and calculate the force produced.
49

Modulating Electro-osmotic Flow with Polymer Coatings

Hickey, Owen January 2012 (has links)
Micro- and nano-fluidic devices represent an exciting field with a wide range of possible applications. These devices, typically made of either silica or glass, ionize when placed in contact with water. Upon the application of an electric field parallel to the wall, a flow is produced by the charged walls called the electro-osmotic flow (EOF). Since electric fields are so often used as the driving force in these devices, EOF is an extremely common phenomenon. For this reason it is highly desirable to be able to control EOF in order to optimize the functioning of these devices. One method which is quite common experimentally is the modification of the surface using polymer coatings. These coatings can be either adsorbed or grafted, and charged or neutral. The first part of this thesis looks at the role of neutral adsorbed polymer coatings for the modulation of EOF. Specifically our simulation results show that for adsorbed coatings made from a dilute polymer solution the strongest quenching of EOF is found for an adsorption strength at the phase transition for adsorption of the polymers. Further evidence is presented that shows that by using a high density of polymer solution and a polymer which has a strong attraction to the surface a very thick polymer layer can be created. Next the case of charged grafted polymer coatings is examined. The variation of the EOF with respect to several key parameters which characterize the polymer coating is investigated and compared to theory. The prediction that the electrophoretic velocity of the polymers is the same as the EOF generated by a coating made up of the same polymers is found to be false though the two values are quite close. The last section presents results which show how hydrodynamic interactions in charged polymer systems can be modeled mesoscopically without the use of explicit charges by forcing a slip between monomers and the surrounding fluid. This model is validated by simulating some surprising predictions made in the literature such as an object with no net charge having a non-zero force when subjected to an electric field, and how the velocity can even be perpendicular to the applied electric field. The thesis can be roughly divided into two topics: using polymer coatings to modulate EOF, and the free solution electrophoresis of polyelectrolytes. While EOF and free solution electrophoresis might seem unrelated it will be shown that the concepts are the same in both cases. In fact while not investigated in this thesis, the mesoscopic simulation methods for electrophoresis could be applied to the modulation of EOF with polymer coatings allowing for the simulation of longer length and time scales or more complex systems such as heterogeneously grafted colloids.
50

Application of EHD-enhanced drying technology: a sustainable approach for Vietnam’s agricultural product processing in the future / Ứng dụng công nghệ sấy cải tiến EHD nhằm phát triển bền vững các quá trình sấy khô nông sản tại Việt Nam trong tương lai

Vu, Anh Tuan, Do, Thi Tam, Vu, Anh Ngoc, Pham, Van Lang, Feng, Feng Chyuan 08 December 2015 (has links) (PDF)
Drying contributes a significantly important role in processing of agricultural products in Vietnam, particularly for high-value agricultural exports. Conventionally thermal-based drying techniques have remained critical disadvantages in term of enhancing product quality and process efficiency. The typical disadvantages include deterioration of organoleptic and nutritional properties, highenergy consumption, expensive costs yet low efficiency and hazards to environment change due to the consumption of fossil fuel sources. Electrohydrodynamics (EHD) drying technology has been demonstrated as an innovative solution for drying enhancement in various applications. This paper aims at an overview of the state-of-the-art EHD drying technology to enhance heat and mass transfer in agricultural drying processes. A case study is then presented to demonstrate an even better process efficiency, compared to the state-of-the-art EHD drying technology, and to shorten the gap “research-to-market”. Finally, this study shows obviously potential applications of this innovative technology in sustainable development of food and post-harvesting agricultural processing for Vietnam in the future. / Sấy khô đóng một vai trò quan trọng trong việc chế biến và bảo quản nông sản sau thu hoạch tại Việt Nam, đặc biệt đối với các mặt hàng nông sản cao cấp phục vụ xuất khẩu. Các phương pháp sấy khô bằng nhiệt truyền thống tồn tại nhiều nhược điểm trong việc nâng cao hiệu quả sấy và bảo đảm chất lượng nông sản. Những nhược điểm nổi bật bao gồm: biến đổi thành phần hóa học và giảm giá trị dinh dưỡng của nông sản sau sấy do sử dụng nhiệt trong quá trình sấy, tiêu hao nhiên liệu lớn, chi phí nhiên liệu, lắp đặt và duy trì hệ thống sấy cao nhưng hiệu suất thấp và đặc biệt ảnh hưởng tới môi trường do sử dụng các nguồn nhiên liệu hóa thạch. Công nghệ sấy cải tiến khíđiện động lực học (EHD) hiện tại đã cho thấy tiềm năng thay thế các phương pháp sấy truyền thống. Bài báo tập trung giới thiệu cơ chế sấy các sản phẩm nông sản bằng công nghệ EHD; qua đó tác giả giới thiệu một mô hình sấy đã chế tạo thành công cho hiệu quả thậm chí còn cao hơn các mô hình hiện tại, đồng thời dễ dàng triển khai trong ngành công nghiệp sấy khô nông sản. Nghiên cứu này chỉ ra tiềm năng ứng dụng to lớn của công nghệ EHD trong phát triển bền vững các quá trình sấy khô nông sản cao cấp tại Việt Nam trong tương lai.

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