Tiểu luận 25 trang, cỡ chữ 13 1 trang 3 hình Bố cục Bìa Lời cám ơn Mục lục Danh sách hình Danh sách bảng Từ viết tắt Chapter 1 Outverview Chapter 2 Định nghĩa, phân loại, cấu tạo, nguyên lí hoạt động,[.]
Tiểu luận 25 trang, cỡ chữ 13 trang hình Bố cục: - Bìa - Lời cám ơn - Mục lục - Danh sách hình - Danh sách bảng - Từ viết tắt Chapter 1: Outverview Chapter 2: Định nghĩa, phân loại, cấu tạo, nguyên lí hoạt động, ứng dụng, thông số, ưu nhược điểm Chapter 5: kết luận tài liệu tham khảo THEO THỨ TỰ SÁCH TÀI LIỆU WEB NÊN CÓ MẤY NGUỒN CHƯA ĐÁNH SỐ DO LÀ WEB NHỚ CHECK XEM YB DỊCH GG DỊCH ĐÚNG KO KHƠNG THÌ HỎI LẠI YB OUTVERVIEW 1.1 Introduction to microwave drying technology Food and agricultural products, after being processed, are always subject to pathogens such as fungi, bacteria, viruses, spore forms, etc available in food, agricultural products, packaging materials or in the air These agents can damage the product before reaching the user, can cause toxins, diseases, etc Therefore, these products need preservation and sterilization measures to ensure quality This is considered a big challenge for the post-harvest preservation and agricultural and food processing industry In the past, people and small businesses often used heat drying methods such as sun drying and boiler drying in preserving and processing products However, this method takes a long time, makes it difficult to retain all the nutrients available in agricultural products, and carries the potential risk of harmful bacteria such as E.coli and mold entering Applying microwave technology can help people and small businesses find new directions in processing and preserving agricultural products and food The advantage of microwave drying technology is that heat is penetrated by microscopic waves, causing all ingredients in the product to be dried in a very short time This method not only saves electricity but also retains most of the nutrients and original color of agricultural products and foods Microwaves (ultra-high-frequency waves - microwaves) are a form of non-ionizing electromagnetic radiation, with frequencies ranging from 300 MHz to 300 GHZ (wavelength λ ranging from 1m to mm), located in the middle of the radio wave range, (RF) and infrared + visible light regions In the microwave range, the frequencies 915 MHz and 2.45 GHz are commonly used for microwave ovens Residential microwave ovens often use a frequency of 2.45 GHz, a wavelength of 12.2 cm (4.80 inches), and the ability to penetrate the physical environment from - cm Large industrial/commercial microwaves often use 915 MHz frequency, 32.8 cm (12.9 inch) wavelength, higher penetration ability from - 22 cm Microwaves, when transmitted through food, heat them Water, fat, and substances in food absorb energy from microwaves in a process called dielectric heating Microwave energy is provided at the molecular level through the molecular interaction of matter with the electromagnetic field, in particular, through molecular friction, which results from the rotation of the electric dipole of the molecule along fluctuations of the electromagnetic field The main mechanism of microwave heating is rotation electric dipole and ionic polarization (Dipolar polarization Mechanism) In addition, there is also an auxiliary heating mechanism, when under the effect of an electric field, ions in a solution will move throughout the solution and collide with each other and convert kinetic energy into heat (conduction mechanism - Conduction mechanism) Thus, only materials with large enough polarity will have the expected results for microwave heating Water in food is the main component of the electric dipole, which plays a huge role in dielectric heating With an electric dipole structure, there are positive and negative charges at both ends, so the water molecules will rotate parallel to the external electric field The alternating electric field oscillation reverses the rotation of the molecules, colliding with other molecules and forcing them into motion, leading to the conversion of this scattered energy into thermal energy At ultrahigh frequencies, the molecules continuously reverse, creating high energy conversion, leading to very rapid heating The volumetric heating rate (Q) of microwaves at a location is proportional to the electric field intensity according to the expression: Q 2f o " E Where f is the frequency of the microwave, E is the electric field strength of the wave at the observation site, o is the vacuum dielectric " constant, and is the energy loss factor in the representative dielectric material for the material's ability to absorb microwaves 1.2 Development history and research needs to be promoted 1.2.1 Development history The application of microwaves to heat food dates back more than 70 years, beginning as a product of radar technology developments during World War II Later, Percy Spencer is considered the inventor of the modern microwave oven from radar technology developed during the war The product was named "Radarange" and was first sold in 1946 A home microwave oven built by Tappan in 1955 provided an innovative patent However, due to its large size and high price, the development of this product on the market is limited It was not until 1967 that Amana Corporation's Countertop microwave ovens began to be used in households 1.2.2 Research needs to be promoted Developing microwave technology for food sterilization requires promoting the following research: 1) Scientific and technological research to provide a stable, evenly distributed electromagnetic field model with high energy efficiency 2) Meet the criteria, including: - Stability of systems and processes - Scientific basis/means to develop the treatment process - Food safety (These criteria are approved by the US Food and Drug Administration FDA (USA Food & Drug Administration).) 3) Ensure high quality food 4) Bring economic efficiency Thus, microwaves have the ability to quickly and strongly heat food, especially products that contain moisture or water, and have been used successfully to heat, dry, and sterilize many types of products food The microwave drying and sterilization system includes a microwave generation system, guiding the waves to the location where the food is placed and using heat in the food for sterilization Microwave drying and sterilization are similar to many other heat methods, including: - The method of using temperatures higher than the maximum temperature of microorganisms to denature the molecules (structure, function) of microbial cells to destroy them Common equipment for autoclaving/sterilization is autoclave, boiling device, hot air chamber The characteristics of this method are the requirement to maintain the temperature and time necessary to kill each type of bacteria Boiling liquid (100 0C for 30 minutes) can kill most microbial cells, except for some species in spore form In addition, using saturated steam under high pressure (pressure cooker up to 1210C) can destroy heat-resistant endospores - The method of using moderate heat (Pasteu pasteurization method) is also a widely used method This method does not kill all microbial cells, but rather controls them and slows down the growth their growth and development in the product For example, to pasteurize milk, the temperature is usually around 710C for 15 seconds, allowing to kill disease-causing bacteria such as Tuberculosis, Brucellosis, Q fever, typhoid fever, etc This method is simple and quite effective However, when sterilizing large equipment and the heat exchange process is long, this solution is not effective Microwave sterilization usually uses high temperature methods, up to 1210C 1.3 Status of research and application of microwave drying technology in the world and in Vietnam Microwave equipment for continuous liquid flow can be used for milk and juice processing (Figure 1) Microwaves for ready meals were also commercially successful in European countries, although American industry remained reluctant to adopt the technology Figure 1: Microwave sterilization system for continuous flow of liquid food [1] It cannot be simple to replace conventional heating with microwave energy To solve this problem we need to fully understand the heating process for the actual product type and the inactivation mechanism, temperature distribution in laminated foods and other important factors The qualitative and significant variation in the heating zone must be taken into consideration in the calculations of the efficiency noted by the electromagnetic connection with energy transfer in ultrahigh frequency sterilization Currently, drying and sterilization using microwave energy are being focused on solid foods Micro device Commercial size corrugated iron is now ready for applications for drying or pasteurizing and sterilizing products according to human needs Microwave technology - for drying, sterilization, or a combination of both - is an advanced technology that does not use chemicals, saves energy, productivity, high efficiency and protects the environment 1.3.1 Research situation of microwave drying technology in Vietnam In fact, microwave sterilization method has not yet been widely applied in practice in Vietnam The main reason is that equipment and technology depend on foreign countries, expensive imported equipment increases production costs Microwave sterilization technology is a new, advanced technology that can sterilize many different products, so it needs to be thoroughly researched in Vietnam To be usable, the equipment must be uncomplicated, automatic, easy to manufacture, operate safely, and be able to sterilize processed foods for export Through surveying the research situation on the application of ultra-high frequency waves in the country, it can be observed that ultra-high frequency wave applications focus on heat processing processes in industrial production: - Van Thanh Company has invested in production technology in a closed, fully automated line in all stages of steaming, vulcanizing, rubber shaping, rainwater cleaning, microwave drying and sterilization , to drying the finished product - Minh Du Information Company Limited (70Bis Tran Dinh Xu, Co Giang Ward, District 1, Ho Chi Minh City) has just researched and successfully manufactured the Gosaviba 20 fresh wood dryer This is the first type of wood dryer to be manufactured A domestic company manufactures on the principle of using microwaves to break water particles out of wood - Topic (Ho Chi Minh City Department of Science and Technology 2012) by Dr Le Anh Duc (HCM City University of Agriculture and Forestry) researches technology and equipment for drying pollen in batches using microwaves In the field of sterilization, on the domestic market there are small machines that sterilize milk bottles for children for family use In the field of industrial production, there are currently no studies using ultrahigh frequency waves for sterilization 1.3.2 Research status of microwave treatment technology in the world Abroad, ultra-high frequency waves are researched and applied very strongly Microwave ovens were proposed in 1940 and are now commonly used all over the world In addition, there are many small machines that use ultra-high frequency waves such as nylon gluing machines, stoves, etc In the field of food processing on an industrial scale, research and applications are very rich We can mention a few highlights as follows: - Hossein Ameri Mahabadi and other authors from the Department of Bioprocess Engineering at Teknologi University in Malaysia used 2.45 GHz ultrahigh frequency waves to control insects in wheat - European Patent No 88110896 dated July 7, 1988 proposes a way to reduce ultrahigh frequency furnace leakage during processing - D Martin and other authors of IEEE magazine addressed the problem of controlling magnetron lamp power for ultrahigh frequency furnaces - Abderraouf Methlouthi and other authors of the COMSOL conference in Paris in 2010 presented research on ultrahigh frequency furnaces with passing product lines - Panya Daungvilailux of the 2011 TSME conference on mechanical engineering presented on drying cashews on a continuous conveyor belt - APV Baker Company (UK) presented the ultra-high frequency cake drying system Figure 2: Ultra-high frequency cake drying system of APV Baker Company (UK) [1] - Microwave Heating Company presents the application of ultrahigh frequency furnaces in rubber vulcanization - Research works by Washington State University (WSU) showed results when treating packaged foods in pressurized hot water and simultaneously heating the product with ultrahigh-frequency waves at a frequency of 915 MHz At this frequency, the waves penetrate deeper into the product than the 2.45 GHz waves of a home microwave Processing time is to minutes and product quality is kept higher than with processed food processing methods Since 2012, research results have been transferred to equipment manufacturing enterprises Figure 3: WSU's microwave sterilization system for ready-to-eat meals [1] Đoạn ghi lấy tên tài liệu là: Nguyễn Đình Uyên, Trần Văn Sư Đào Quốc Hưng, “Hướng ứng dụng cơng nghệ sấy vi sóng bảo quản, chế biến nông sản thực phẩm.” Báo cáo phân tích xu hướng cơng nghệ, 2019 Ảnh có [1] lấy tài liệu [1] CHAPTER 2: 2.1 Definitions 2.1.1 Electromagnetic waves Also known as electromagnetic radiation, it is a combination of electric and magnetic fields oscillating perpendicular to each other Characteristics of electromagnetic waves: - Spread in environments: Electromagnetic waves can propagate in liquid, solid, gas and vacuum media They are the only type of wave that can propagate in a vacuum environment - Has the properties of mechanical waves: Electromagnetic waves have properties similar to mechanical waves such as refraction, reflection, And comply with the laws of straight transmission, refraction, interference, - Electromagnetic waves are transverse waves: Electromagnetic waves are parallel, which can be understood as the propagation of oscillations related to the directional properties of particles whose direction of vibration is perpendicular to the direction of wave propagation - Electromagnetic waves from the energy network: Electromagnetic hc waves carry energy and the energy of a photon with wavelength is , where h is Planck's constant and c is the speed of light in a vacuum environment Therefore, the longer the wavelength, the smaller the photon energy will be DO LÀ TRÌNH BÀY THEO THỨ TỰ (SÁCH -TÀI LIỆU- WEB) NÊN GHI SAU THỨ TỰ MẤY TÀI LIỆU YB ĐÃ ĐÁNH NHÁ: [ ] “Sóng điện từ gì”- vuihoc.vn 2.1.2 Microwaves Microwaves (or microwaves / shortwaves) are electromagnetic waves with wavelengths longer than infrared rays, but shorter than radio waves (with wavelengths from 1mm to 1m) The nature of microwaves is that electromagnetic waves propagate at the speed of light Microwaves lie in the electromagnetic spectrum between the infrared and radio waves They have a wavelength between 0.01 and 1m and are typically effective in the range between 0.3 and 30 GHz However, we usually use 2.45 GHz Fig 4: Schematic illustration of the electromagnetic spectrum 2.2 Classification Below is the classification of industrial microwave ovens according to their functions: - Continuous conveyor dryer: divided into many types of machines serving different industries such as: drying system used to defrost meat by microwave, system for inflating food by microwave, wood dryer microwave dryer, microwave chemical material dryer, microwave paper dryer, microwave pharmaceutical dryer - Rotary dryer: mainly used for the ceramic industry, heating ceramic products without affecting the product such as cracking or breaking the product Including many types of machines such as microwave vacuum dryers, microwave ceramic sintering furnaces, microwave high temperature furnaces - Microwave liquid dryer: mainly used for liquid sterilization - Heat pump dryer: mainly used for fields such as drying wood, food and processing agricultural by-products such as seafood and fruit dryers, incense dryers Other products [ ] “Lị vi sóng cơng nghiệp”-visong.vn 2.3 Operating Principles The material to be dried is moved by the conveyor belt into the furnace chamber Microwave energy interacts with the polar molecules and ions of the material When the field reverses, it relaxes and allows the molecules to return to their random orientation This interaction of the alternating field with the ions causes collisions This impact energy is also converted into heat The heat generated inside the material causes the moisture to evaporate and then diffuse to the solid surface Thus, rapid mass transfer is achieved At the same time, a stream of hot air is also passed through the dryer so that moisture is swept away from the solid surface Fig 5: Operating Principles 2.4 Application 2.4.1 Application of microwave drying For the Food Industry: The characteristic of drying the product is to remove all the moisture in the ingredients to be dried while still ensuring the color, flavor and nutrients in the food are retained Microwave technology not only helps dry but also has the ability to sterilize, deodorize the product, roast it and retain the delicious flavor of the finished product after it comes out of the oven Applications of microwaves in the food technology industry can include applications in the production of cereal powder, instant packaged products, teas, cakes, snacks, and protective foods health and beauty care Wood processing industry: Drying paper or wood products helps destroy termite and termite eggs in the wood fibers, helping to weld the seams of laminated wood correctly In particular, wood drying time is fast, can dry wood types from - cm thick, dried wood products not crack, break or warp Fig 6: Microwave drying in the wood processing industry [ ] SỐ Ở LINK DƯỚI Rubber production industry: Industrial drying systems are often used in the process of heating and vulcanizing rubber (this is the name of the technique of increasing rubber hardness by heating, and giving rubber combined with sulfur - vulcanized) often used in the production of tires, and rubber tools with high requirements for durability Microwave technology allows the product to absorb a uniform layer of heat, creating a product with even surface durability and a relatively short rubber vulcanization time, reducing costs and increasing the competitiveness of businesses on the market Figure 7: Microwave drying in rubber vulcanization The main application of microwave technology in the pharmaceutical chemistry industry is drying and sterilizing powder, tablet, granular or liquid products In particular, herbal products and Oriental medicine drugs that need to be dried and sterilized are very suitable when done with microwave drying equipment Other industries: Coal production industry, ceramic industry, chemical industry and other industries [ ] “Lị vi sóng cơng nghiệp”-visong.vn 2.4.2 Drying technology using radio waves RF waves have operating frequencies in the range from MHz to 300 MHz There are three operating frequency values used in industry: 13 MHz, 27 MHz and 40 MHz (Electron Code Fed.Regul (ECFR), 2017) The RF heating mechanism is a volumetric heating mechanism on the entire drying material that will help increase the heating speed, the temperature is evenly distributed over the entire material volume, helping the moisture diffusion process take place quickly during the drying process helps shorten drying time (Yang et al., 2018) Author Balakrishnan and collaborators (2004) Yunyang Wang and collaborators (2012) Yunyang Wang and collaborators (2013) Wang and collaborators (2014) Zhou and collaborators (2018) Material Drying synthetic leather Drying with RF or combining RF with other Drying macadamia nuts drying methods helps Drying almonds with hot increase heating speed, temperature and moisture air and RF waves Drying Macadamia nuts evenly distributed over the with hot air and RF waves volume of dried material Drying walnuts Drying cereal grains using fluidized bed and RF waves Drying rice by convection Piyachat (2012) of hot air with RF waves Drying peanuts with hot Jiao and collaborators air combined with RF (2016) waves Jumah (2005) Result Drying with RF or combining RF with other drying methods helps improve speed and enhance the quality of dried products in both nutrition and sensory aspects Table Radio waves in drying technology [2] [2] Nguyễn Hay, Lê Anh Đức, Phạm Văn Kiên, “Nghiên cứu kĩ thuật sấy nấm linh chi Việt Nam”, luận án tiến sĩ năm 2020 2.5 Technical parameters 2.5.1 8kW Aroma dryer - Name: Vegetable/fruit/food dehydrator - Type: Box type - Model: X8 - Microwave frequency: 2450±50 MHz - Input voltage: 380V±5% - Microwave power: 8kw - Color of the oven: Silver-white - Material of the oven: Industrial stainless steel Figure 8: 8kW Aroma dryer 2.5.2 12kW microwave drying Cabinet - Model: EVS/12KW - Microwave frequency: 2450 ± 50 MHz - Input voltage: 380V ± 5% - Capacity: 12KW - Material: industrial stainless steel - Temperature: 60 -120°C - Weight: 200 kg - Dimensions: 1600mm x 1550mm x 1100mm - Installation area: ≤ 3m2 Figure 9: 12kW microwave drying Cabinet 2.5.3 Microwave coveyor dryer 20kW - Power supply: phase 380V, 50 Hz, neutral wire must be as large as phase wire - Rated input power: 25 KVA - Microwave output power: 20KW - Microwave frequency: 2450 MHz ± 50 MH - Device size: 8600 x 825 x 1750 (mm) - Microwave effect area size: 4600 x 665 x 520 (mm) - Transmission belt width: 500 mm - Transport belt height above ground: According to customer requirements - Transmission speed: m/min (adjustable) - Electromechanical drive: 0.75KW (adjustable) - Ambient temperature: -10 - 40 ℃ (relative humidity ≤ 80%) (relative humidity ≤ 80%) - Working environment requirements: no excessively corrosive gases around, no flammable or explosive gases - Number of microwave chambers: groups (2300 x 665 x 520* 2) (mm) - Microwave loading method: Feed source above the machine - Pressure unit opening height: 60 mm - Magnetron cooling method: Air cooling - Temperature measurement range: - 300 oC - Accuracy: ± oC (equipped with infrared temperature sensor) - Control method: Equipped with PLC automatic controller, HMI touch screen and LCD screen for direct observation of the furnace Figure 10: Microwave coveyor dryer 2.6 Advantages and disadvantages 2.6.1 Advantages - Ultra-high frequency waves penetrate deeply into food ingredients, so the heating process occurs over the entire volume of food to be processed and takes place evenly and quickly, significantly reducing processing time and energy consumption; - Because the heat transfer process takes place quickly, the nutrients, vitamins as well as the taste, feel, and color of the food are well preserved; - Pasteurization or ultra-fast sterilization of liquids minimizes loss of nutrients, color and flavor; - Minimizes residue and precipitation by eliminating heat transfer through the surface - High thermal efficiency (80% or more); - Microwave shape facilitates cleaning in place (CIP); - Suitable for heat-sensitive, highly viscous and multi-phase fluids; - Low system maintenance costs; - The system makes no noise and does not produce emissions; - The radial temperature profile is similar for most products; - Can be combined with other technologies such as regenerative heat exchange and infrared heating to create better processing functions 2.6.1 Disdvantages a) Microwave sterilization has been widely studied both academically and industrially However, the commercialization of this process has been a great success in the form of home microwave ovens The biggest limitation in industrial microwave drying and sterilization is that the actual temperature profiles of the products are not available, so research is needed to determine these characteristics In addition, the nature of microwave ovens is that heat is not evenly distributed, so mass-dried or sterilized products may not have high uniformity b) If the microwave heating process is not carried out under optimal conditions, it will not ensure better quality of the food after processing Previously, Swiss scientist Hans Hertel was the first to study the risks that microwaves pose to nutrition When microwave radiation destroys and deforms food molecules, new harmful compounds (radilytic compounds) are formed These compounds harm the body in many ways The deterioration of quality, sensitization, and nutrition depends on many factors such as the nature of the food, geometrical configuration, dielectric properties, and the design of the heating furnace compared to the treatment method normal heat The dielectric properties of foods vary significantly during heat treatment and especially above 800C for proteins and starches, and at the same time heat absorption occurs Changes in dielectric properties can affect the quality of the heating zones, while in conventional heat treatment these factors are not important The connection of heat transfer and electromagnetic fields can serve to account for changes in dielectric properties upon heat treatment The above limitations have been focused on by many scientists, technologists and technicians As a result, microwave ovens are now commonly used in food and food preparation