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Unit operations in chemical engineering
The individual processes used by chemical engineers (e.g. distillation or chlorination) are called unit operations and consist of chemical reaction, mass-, heat- and momentum- transfer operations.
In chemical engineering and related fields, a unit operation is a basic step in a process. A process may have many unit operations to obtain the desired product.
In 1923 William H. Walker, Warren K. Lewis and William H. McAdams wrote the book “The Principles of Chemical Engineering” and explained the variety of chemical industries have processes which follow the same physical laws. They summed-up these similar processes into unit operations. Each unit operation follows the same physical laws and may be used in all chemical industries. The unit operations form the fundamental principles of chemical engineering. Most unit operations are based mechanistically upon the fundamental transport processes of mass transfer, heat transfer, and fluid flow (momentum transfer). Unit operations based on fluid mechanics include fluid transport (such as pumping), mixing/agitation, filtration, clarification, thickening or sedimentation, classification, and centrifugation. Operations based on heat transfer include heat exchange, condensation, evaporation, furnaces or kilns, drying, cooling towers, and freezing or thawing. Operations that are based on mass transfer include distillation, solvent extraction, leaching, absorption or desorption, adsorption, ion exchange, humidification or dehumidification, gaseous diffusion, crystallization, and thermal diffusion. Operations that are based on mechanical principles include screening, solids handling, size reduction, flotation, magnetic separation, and electrostatic precipitation.
Therefore, chemical engineering unit operations consist of five classes:
1. Fluid flow processes, including fluids transportation, filtration, solids fluidization
2. Heat transfer processes, including evaporation, condensation
3. Mass transfer processes, including gas absorption, distillation, extraction, adsorption, drying
4. Thermodynamic processes, including gas liquefaction, refrigeration
5. Mechanical processes, including solids transportation, crushing and pulverization, screening and sieving
Chemical engineering unit operations also fall in the categories such as combination (mixing); separation (distillation); reaction (chemical reaction). Chemical engineering unit operations and chemical engineering unit processing form the main principles of all kinds of chemical industries and are the foundation of designs of chemical plants, factories and equipment used.
4. Answer the questions to the text:
1. What is a unit operation in chemical engineering and related fields?
2. What did William H. Walker et al explain in the book “The Principles of Chemical Engineering”?
3. What fundamental transport processes are most unit operations based upon?
4. What classes do chemical engineering unit operations consist of?
5. What do chemical engineering unit operations and chemical engineering unit processing form?
5. Form derivatives from the following words and translate them into Ukrainian:
6. Fill in the gaps using the terms denoting unit operations from the table below:
1. _____ is a physical water treatment process used to settle out suspended solids in water under the influence of gravity.
2. _____ is a type of phase transition; it is the process by which molecules in a liquid state (e.g., water) spontaneously become gaseous
3. _____ is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture.
4. _____ is commonly the mechanical or physical operation which is used for the separation of solids from fluids (liquids or gases) by interposing a medium through which only the fluid can pass.
5. _____ is the incorporation of a substance in one state into another of a different state
6. _____ is the practice of taking granulated ore material and separating it into multiple grades by particle size.
7. Match the columns to make up word combinations and translate them into Ukrainian:
8. Translate into English using a technical dictionary:
1. При хімічній абсорбції компонент, який абсорбується, зв'язується в рідкій фазі у вигляді хімічної сполуки.
2. Ректифікацію застосовують у хімічній, нафтовій, спиртовій промисловості, а також для розділення ізотопів, виділення індивідуальних речовин тощо.
3. До теплообмінного апарату належать випарники, економайзери, льодогенератори, парогенератори, повітронагрівачі, градирні тощо.
4. Застосовують теплообмінні апарати у теплоенергетиці, промисловості, сільському господарстві, системах вентиляції та опалення тощо.
5. Простим типом лабораторного холодильника є повітряний, що представляє собою зазвичай просто скляну трубку, яка охолоджується навколишнім повітрям.
6. Екструзія — процес отримання виробів шляхом екструдування розплаву матеріалу через формуючий отвір.
Pick up the key words from the text “Unit operations in chemical engineering”. Make up your own sentences with them.
10. Write an abstract to the text “Unit operations in chemical engineering”.
Get ready for presenting the topic “Unit operations in chemical engineering” at the conference ”Innovations in Science and Engineering” based on the following questions of Task 4.
1. Read and memorize the following words:
2. Read and memorize the following word combinations:
3. Read and translate the text into Ukrainian:
Drying is one of the most frequently encountered chemical engineering operations. Drying generally signifies the removal of liquid from a solid by evaporation, although gases are also dried.
Industrial dryers are used for removing moisture from substances, products or materials in a business or manufacturing capacity. The term "industrial dryer" is a general reference that applies to dryers no matter what their particular method of drying is: air, infrared or spray drying. Because of the variety, there is no single design or model of industrial dryer, though there are some shared characteristics.
Many dryers are made from stainless steel because it is strong, sanitary and corrosion resistant. They are often cylindrical tanks or rectangular boxes with multiple intake and output valves, connections, openings, gauges and controls. Some may be continuous-able to dry a constant flow of materials and utilize a conveyor belt while others work in batches. The capacity depends on the kind of dryer and the material that will be dried. Certain dryers can dry over 25,000 pounds an hour while others can be built to hold only one cubic foot. Dryers are essential for the pharmaceutical, food processing, manufacturing, agricultural, pollution control, water treatment and paper industries and have multiple functions when working with chemicals, dairy products, fertilizers, grains, minerals, paper, plastics, refuse and more.
Most industrial dryers are bolted or welded together, depending on the importance of the seams, the anticipated product and any motion the dryer will endure. The three main methods of drying encompass a variety of models that carry out the task in different ways.
Air dryers are the most common industrial dryers. They bring materials into direct contact with hot air which causes moisture to evaporate and diffuse into the air, leaving behind a dry product.
Flash dryers, freeze dryers, fluid bed dryersand rotary dryers all fit in this category though their designs vary. Flash dryers use a short intense burst of heat to dry materials almost instantly while freeze drying uses cold air and vacuums to freeze moisture and sublime it away.
Fluid bed dryers shoot steam up through a perforated plate in order to cause the solid material to behave like a fluid; rotary dryers are large drums that dry products as they turn and tumble the material through the hot air contained inside.
Infrared dryers rely on electromagnetic radiation from a certain segment of the wavelength to dry solid materials quickly and without overheating them because the wavelength can be matched to the absorption rate of the product to maximize energy and resources.
Spray drying introduces the material to jets of hot steam which causes the moisture to flash dry and evaporate. Spray drying is highly suited for the continuous production of dry solids in either powder, granulate or agglomerate form from liquid feedstocks as solutions, emulsions and pumpable suspensions. Therefore, spray drying is an ideal process where the end-product must comply to precise quality standards regarding particle size distribution, residual moisture content, bulk density, and particle shape.
4. Answer the questions to the text:
1. What does drying signify?
2. What are main methods of drying?
3. What shared characteristics do industrial dryers have?
4. What are dryers essential for?
5. What is the principle of action of air dryers?
6. What do flash dryers use to dry materials?
7. What dryers rely on electromagnetic radiation from a certain segment of the wavelength?
8. What is spray drying highly suited for?
5. Complete the word combinations according to the context and translate them into Ukrainian:
6. Match the words from the text with their synonyms on the right:
7. Point out the sentences containing information directly from the text:
1. Because of the variety, there is no single design or model of industrial dryer, though there are some shared characteristics.
2. Fluidized spray dryers are operationally flexible and enable production of a wide range of physical properties and optimum thermal efficiency because of the drying at the low temperature.
3. Flash dryers are extensively used for drying powders and granules, crystalline material.
4. Many dryers are made from stainless steel because it is strong, sanitary and corrosion resistant.
5. All spray dryers use some type of atomizer or spray nozzle to disperse the liquid or slurry into a controlled drop size spray.
6. The three main methods of drying encompass a variety of models that carry out the task in different ways.
7. In chemical synthesis, products are often freeze-dried to make them more stable, or easier to dissolve in water for subsequent use.
8. Spray drying introduces the material to jets of hot steam which causes the moisture to flash dry and evaporate.
9. Air heating increases the driving force for heat transfer and accelerates drying.
10. Every spray dryer consists of feed pump, atomizer, air heater, air disperser, drying chamber, and systems for exhaust air cleaning and powder recovery.
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