Английский язык. Учебное пособие для студентов направления подготовки бакалавров 151000 «Технологические машины и оборудование» (профиль «Машины и апп

EXERCISES

1. Remember the pronunciation of the following words:

mixture, aperture, temperature, feature, structure, moisture, fracture. Translate them. Why are they placed together?

2. Form the missing words from the following verbs and translate them.

3. Find the correct form of the word on the left so that it can be used on the right.

4. Vocabulary. Translate the following word combinations from Russian into English:

классификация твердых частиц, фракции различного размера, метод просеивания (грохочения), плотность частиц, электромагнитные свойства материала, поверхностные свойства, дырчатая (перфорированная) пластина.

5. Translate the following word combinations into Russian:

liquid overflow, receptacles, to clog in the apertures of the screen, terminal falling velocity, mesh, woven wire cloth, settling tank.

6. Раy attention to the proper translation of the words CAUSE, BECAUSE, BECAUSE OF.

1. Liquid overflow causes the very fine particles to move forward. 2. Large particles collect near the inlet of the settling tank because of their high

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terminal falling velocity. 3. When separating a material into size fractions a sieving method is used, because this process depends primarily on the size of the particles. 4. A small force will cause fracture, provided it is maintained for a sufficient time. 5. Low terminal falling velocity is the cause that makes small particles to settle far from the inlet of the settling tank. 6. A great force will cause the particle to fracture. 7. All particles are separated in a fluid because of the clogging in fine apertures of the screen.

7. Mind the different words: VOLUME, VALVE and VALUE.

1. In a tank there is a relatively large volume of water moving at a low velocity. 2. The frequency of opening the valves is controlled independently. 3. The value of gravity is assumed constant.

8. Look at Fig.7 and try to describe the process.

II. Skim Text 10B and try to understand what is about and what information is known to you.

Text 10B

CURD

Curd is a dairy product obtained by curdling milk with rennet or an edible acidic substance such as lemon juice or vinegar and then draining off the liquid portion (called whey). Milk that has been left to sour will also naturally produces curds, and sour milk cheese is produced this way. The increased acidity causes the milk proteins (casein) to tangle into solid masses, or "curds". The rest, which contains only whey proteins, is the whey. In cow's milk, 80% of the proteins are caseins.

Curd products vary by region and include cottage cheese, quark (both curdled by bacteria and sometimes also rennet) and paneer (curdled with lemon juice).

Cottage cheese is a fresh cheese curd product with a mild flavor. It is drained, but not pressed, so some whey remains and the individual curds remain loose. The curd is usually washed to remove acidity, giving sweet curd cheese. It is not aged or coloured. Different styles of cottage cheese are made from milks with different fat levels and in small-curd or large-curd preparations. Cottage cheese which is pressed becomes hoop cheese, farmer cheese, pot cheese, or queso blanco.

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In Asia, curd is essentially a vegetarian preparation using yeast to ferment the milk. In the Indian subcontinent, buffalo milk is used for curd due to its higher fat content making a thicker curd. The quality of curd depends on the starter used. The time taken to curdle also varies with the seasons taking less than 6 hours in hot weather and up to 16 hours in cold weather. In the industry, an optimal temperature of 43°C for 4-6 hours is used for preparation.

However in India, the word 'curd' is used to mean yoghurt. In South India, it is common practice to finish any meal with few cups of 'curd rice', made by mixing rice and yoghurt. It is generally accepted to cool the body in tropical climates and is nutritious.

Cheese curds are popular in some French-speaking regions of Canada as well as in the United States. They are freshly made morsels of cheddar cheese before being pressed and aged. In Quebec, they are popularly served French files. In some parts of the U.S., they are breaded and fried. Fresh cheese curds squeak against the teeth as they are bitten. There are also many popular varieties besides cheddar, such as white cheeses and flavored cheeses (pepper garlic, butter, lemon, etc). The cheeses themselves are not but rather lightly coated with powdered flavor, natural or not, similar to potato chips.

EXERCISES

1.Identify the topic of each paragraph of Text 10B .

2.Answer the following questions and discuss them with your fellowstudents.

1.What is the manufacturing process of the curd?

2.What types of curd do you know?

3.How is the cottage cheese obtained?

4.Does the curd vary by region ?

5.What is the peculiarity of the curd production in India?

6.In what country is the cheese curd popular?

7.Can curd be produced without milk?

3. Give a brief overview of the structure and contents of Text 10B.

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UNIT 11

I. Read and memorize the active vocabulary to the text. Read and translate Text 11A .

Brownian Movement - броуновское движение centrifugal - центробежный

cluster - скопление

colloid - коллоид, коллоидный раствор consolidation - уплотнение

depth - глубина

dilute - разбавленный, разжиженный draining - осушение

expression - выжимание, отжим flocculation - образование хлопьев layer - слой

pure - чистый sediment - осадок

sedimentation tank - отстойник solute - растворенное вещество

volumetric concentration - объемная концентрация

Text 11A

SEDIMENTATION

Concentrated suspensions may be obtained by the process which is called sedimentation. Sedimentation is settling of solids from a solid/liquid mixture in such a way that two layers are formed (a concentrated suspension of the solids with a clear liquid above it). After settling the two layers can be separated by filtration or draining. Sedimentation is used in food processing to clean liquid from undesirable particles and to recover useful food particles from water suspensions. It is also applied in the expression of juices and oils from fruits, vegetables and oilseeds.

There are two methods of carrying out sedimentation: the gravitational and the centrifugal techniques. If the particle is settling in the gravitational field, it rapidly reaches its terminal falling velocity. In a centrifugal field the particle may reach a very much higher velocity because the centrifugal force may be many thousands of times greater than the gravitational force.

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The rate of sedimentation has been found to depend on the particle diameter and density, the viscosity of the liquid. It also depends on the depth and diameter of the containing vessel and the volumetric concentration. The depth of the sedimentation tank should be sufficient for settling the smallest solid particles, while the diameter should be such that the upward velocity of the clear water is lower than the settling velocity of the particles.

Although the sedimentation rate tends to increase steadily with the concentration of the suspension, the particles in very dilute suspensions settle rather quickly due to the formation of clusters of particles.

The rate of sedimentation of a suspension of fine particles is difficult to predict because of the large number of factors involved. Thus, for instance, the presence of an ionized solute in the liquid and the nature of the surface of the particles will affect the degree of flocculation, and, hence, the formation of sediment. A further factor influencing the sedimentation rate is the degree of agitation of the suspension. Gentle stirring can produce accelerated settling and prevent consolidation (agglomeration) of the final sediment.

The rate of sedimentation of particles in a fluid will be very much greater in a centrifugal field than in the gravitational field. The use of a centrifuge permits much more rapid sedimentation and also provides the possibility of effecting separation which would be quite impossible under gravitational conditions. For example, a colloid or emulsion may be quite stable under ordinary gravitational conditions where the dispersive forces such as those due to Brownian Movement are very much greater than the gravitational force. However, in a centrifuge the colloid or emulsion may break down completely because the vastly greater centrifugal forces will be able to overcome the effects of the dispersive forces.

EXERCISES

1. Give the derivatives of the following words:

centrifuge, gravity, disperse, retain, sediment, suspend, solve.

2. Form the nouns and verbs with the prefix DIS-:

advantage, comfort, charge, solve, cover, integrate, appear, continue.

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3. Translate from Russian:

сила гравитации, центробежная сила, осаждение в гравитационном поле, удельная поверхность, объемная концентрация, броуновское движение, фильтрация, осушение, мелкие поры, влага.

4. Translate from English into Russian:

degree of flocculation, dilute suspension, clusters of particles, degree of agitation, stirring, retention of moisture, flocculation, consolidation, settling, ionized solute, layer, surface tension forces, terminal falling velocity.

5. Remember how DEGREES OF COMPARISON are formed.

When it is necessary to express the intensity of the quality, intensifiers are used, e.g.: longer - much longer, very much longer, vastly longer - far longer or vice versa - rather longer, somewhat longer.

6. Translate the following sentences.

1. It is important to know that suspensions of fine particles tend to behave rather differently from coarse suspensions. 2. In a centrifugal field the particle may reach a very much higher velocity because the centrifugal force may be many thousands of times greater than the gravitational force. 3. It is possible to obtain a very much drier solid by centrifugal action than by draining under gravity. 4. The use of centrifuge permits much more rapid sedimentation.

7. Remember all the possible ways of translating the verbs SHOULD and WOULD into Russian. Translate the following sentences.

1. The 1iquid to be dispersed should be forced through an opening under pressure. 2. If the openings were smaller and if the pressure were constant, the droplets formed would be smaller and more uniform. 3. Using this mill, the engineer had to suppose that the output of the whole plant would be decreased. 4. The mechanical engineer should be able to select the most suitable equipment for a certain purpose. 5. A large difference in density of two substances would make mixing more difficult. 6. Had these two substances differed in only one property, there would have been only one possible method of separation.

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II. Skim Text 11B and try to understand what is about and what information is known to you.

Text 11B

FRUITS PROCESSING PLANTS

A large variety of fruits can be used to obtain by the appropriate technological process different kinds of semi – finished product starting from fresh fruits just harvested from field or stored in controlled atmosphere warehouses. The ripeness degree, the freshness and the cleanness of the raw materials are very important to obtain a high quality juice.

A fruit juice can be considered a suspension of water, sugars (manly: glucose – fructose – sucrose), acids, essences, vitamins, proteins, minerals, pigments and pectin-substances.

The technological cycle has to be developed in order to preserve as much as possible the organoleptic properties, the colour and aromas of the fresh fruit. So especially the thermal treatments, which are necessary either to get a god yield in some steps of the process, either to have microbial stability, must be carefully evaluated just to avoid browning phenomena and vitamins and proteins degradation. This treatment is very depending from the fruit PH.

Pectin substances are also very important. For cloudy juices or fruit puree it is essential that the original content of pectins shall be retained throughout the production. In this case fruit enzymes must be inactivated during processing as soon as possible by an heating process.

For clear, filtered juices a breakdown of pectins is needed to enable a good yield and high degree of juice concentration, and this is done by adding specific pectolytic enzymes which hydrolise the pectic substances. To obtain clear juices the enzymation is not the only steps required, but after that other phases such us sedimentation with fining agents (gelatin – bentonite..), and filtration (by vacuum and ultrafiltration) are required.

With the evaporation process, taking out part of the water from the fruit, the juice concentrates can be considered as concentrated sugar-acid solution. Considering this and the low PH of the fruits the puree and juices concentrates are not a suitable substrates for bacteria potentially dangerous for human health.

To obtain the aromas, the secondary condensates are recovered from the evaporator and sent to the aroma recovery plant.

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The product is sterilized before packaging by a tube in tube heater for puree, and pulpy products ,or plate heat exchanger in case of clear or cloudy juices

After cooling the sterilized product is sent to a dedicated filler at one or two filling heads depending from the needed output to fill in multiple layer bags in a controlled atmosphere of live steam to avoid any contamination from the ambient.

The fruit process obviously depends on the raw material and the required final product .

.

EXERCISES

1.Identify the topic of each paragraph of Text 11B.

2.Answer the following questions and discuss them with your fellowstudents.

1.Is the freshness of the raw materials important to obtain a high quality juice?

2.What does the fruit juice contain?

3.What is the role of the thermal treatment in the technological cycle of the fruit production?

4.Are pectin substances important in the fruit processing?

5.What is the technology of the clear juice production?

6.What is obtained during the evaporation process?

7.What is it necessary to do with ready product before packaging?

8.What does the fruit process depend on?

3.Give a brief overview of the structure and contents of Text 11B using the following expressions.

The aim of the text is...

The text is devoted to...

The text can be divided into … parts The first part is about…

The second part deals with…

The third part describes…

To sum up ..

.

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UNIT 12

I. Read and memorize the active vocabulary to the text. II. Read and translate Text 12A .

build up - нарастать, накапливаться

cake filtration - фильтрация с образованием осадка filter cake - осадок от фильтрования

filtering medium - фильтрующая среда funnel - воронка

pore - пора porous - пористый support - опора

variable - переменная (величина)

Text 12A

FILTRATION

The separation of solids from a suspension in a liquid by means of a porous medium or screen which retains the solids and allows the liquid to pass is termed filtration. In the chemical laboratory filtration is often carried out in a conical funnel fitted with a filter paper. In the industrial scale filtration is accomplished mechanically by using various types of filters because of much larger quantities of suspension and solids. A thicker layer of solids has to form and, in order to achieve a high rate of passage of liquid through the solids, higher pressures will be needed and it will be nесеssагу to provide a far greater area. A typical filtration operation is illustrated in Fig. 6 which shows the filter medium, in this case a cloth, its support and the layer of solids or filter cake, which has already formed.

Fig. 6. Filtration operation

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The volumes of the suspensions to be handled will vary from the extremely large quantities involved, in water purification, for example, to relatively small quantities in the fine chemical industry where the variety of solids will be considerable. In most instances it is the solids that are wanted and their physical size and properties are of great importance.

Filtration is one of the most important operations for solid/liquid separation, a large variety of filtration methods being used.

In the typical operation shown in Fig. 6 the cake gradually builds up on the medium and the resistance to flow progressively increases. During the initial period of flow particles are deposited in the surface layers of the cloth to form the true filtering medium. The type of filtration described above is usually referred to as cake filtration. The proportion of solids in the suspension is large and most of the particles are collected in the filter cake which can subsequently be separated and removed from the medium.

The mechanical details of the equipment, particularly of the flow channel and the support for the medium, influence the way the cake is built up and the ease with which it may be removed. A uniform structure is very desirable for good washing and cakes formed from particles of very mixed sizes and shapes present special problems.

The initial stages in the build-up of the filter cake are important because they may have a large effect on the flow resistance and may seriously affect the useful life of the cloth. The blocking of the pores of the filter medium by particles is an involved phenomenon, partly because of the very complex nature of the surface structure of the usual types of filter media. One of the most important variables affecting the tendency for blocking is the concentration of particles. The greater the concentration, the smaller will be the average distance between the particles, аs a result, suspensions of high concentration generally give rise to cakes of lower resistance than those formed from dilute suspensions.

In the filtration, the resistance of the filter cake progressively increases and consequently, in a constant pressure operation, the rate of filtration falls. If the build-up of solids can be reduced, the effective cake thickness will be less and the rate of flow of filtrate will be increased.

There are many factors to be considered when selecting equipment and operating conditions for filtration.

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