Current applications of refrigeration

Probably the most widely-used current applications of refrigeration are for the air-conditioning of private homes and public buildings, and the refrigeration of foodstuffs in homes, restaurants and large storage warehouses. The use of refrigerators in our kitchens for the storage of fruits and vegetables has allowed us to add fresh salads to our diets year round, and to store fish and meats safely for long periods. Dairy products are constantly in need of refrigeration, and it was only discovered in the past few decades that eggs needed to be refrigerated during shipment rather than waiting to be refrigerated after arrival at the grocery store. Meats, poultry and fish all must be kept in climate-controlled environments before being sold. Refrigeration also helps keep fruits and vegetables edible longer.

In commerce and manufacturing, there are many uses for refrigeration. Mechanical refrigeration is applied in a number of industries. It is possible to enumerate about 250 branches of technics where cold is applied. Refrigeration is applied in metallurgical operations, in air conditioning, in chemical and fishing industries and in many other branches of industry.

Industrial air conditioning is used in food, chemical, textile and many other industries. It ensures safety by reduction of fatigue and explosion hazard.

In chemical industry refrigeration is used to liquify gases like oxygen, nitrogen, propane and methane for example. For the latter purpose it is the difference of the boiling points of gases that is made use of. For instance, oxygen at the temperature of -183° C is obtained from liquid air by evaporating its nitrogen that has a lower boiling point, -196° C. In compressed air purification, it is used to condense water vapor from compressed air to reduce its moisture content. In oil refineries, chemical plants, and petrochemical plants, refrigeration is used to maintain certain processes at their required low temperatures (for example, in the alkylation of butenes and butane to produce a high octane gasoline component). Metal workers use refrigeration to temper steel and cutlery. In transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes and sea-going vessels, refrigeration is a necessity.

Other applications are made in manufacture of cigars, in making candy, in the production of photographic films and similar celluloid products, in surgical operations and in excavating operations; this process is accomplished by freezing a ring of quicksand so that tunneling can be done in the hard material. By means of cold, chemical reactions are regulated on which the output and quality of the finished products depend.

There is nothing so valuable as cold to man in the manufacture of explosives, aniline, paints, synthetic rubber, in the metal working industry for tempering some especially fine and important parts of machines creating their artificial aging. Such parts will stand moisture and temperature variations and will keep their initial dimensions for a long time.

Artificial cold is also used in aviation and astronautics – when the work of aviation motors is studied under the conditions of great height, at low temperatures, and in rarefied air.

It is especially important for the development of science to study the behaviour of substances under the conditions of extremely low temperatures near the absolute zero when it is easier to study the structure of the invisible world of atoms and molecules.

 

* * *

1. What is the most widely-used application of refrigeration?

2. What does the use of refrigeration allow to do us at home?

3. Where is cold applied?

4. What is used in food and textile industries?

5. What is refrigeration used in chemical industry to?

6. What do metal workers use refrigeration to?

7. Where is it necessary to use refrigeration?

 

VI. Read and translate the text:

 

Refrigeration

Refrigeration is the process of removing heat from an enclosed space, or from a substance, and rejecting it elsewhere for the primary purpose of lowering the temperature of the enclosed space or substance and then maintaining that lower temperature. The term cooling refers generally to any natural or artificial process by which heat is dissipated. The process of artificially producing extreme cold temperatures is referred to as cryogenics.

Cold is the absence of heat, hence in order to reduce a temperature, one does not "add cold", rather one "removes heat." In order to satisfy the Second Law of Thermodynamics, some form of work must be performed to accomplish this. This work is traditionally done by mechanical work but can also be done by magnetism, laser or other means. However, all refrigeration uses the three basic methods of heat transfer: convection, conduction, or radiation.

Methods of refrigeration can be classified as non-cyclic, cyclic and thermoelectric.

Non-cyclic refrigeration: in these methods, refrigeration can be accomplished by melting ice or by subliming dry ice. These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable coolers.

Ice owes its effectiveness as a cooling agent to its constant melting point of 0 °C (32 °F). In order to melt, ice must absorb 333.55 kJ/kg (approx. 144 Btu/lb) of heat. Foodstuffs maintained at this temperature or slightly above have an increased storage life. Solid carbon dioxide, known as dry ice, is used also as a refrigerant. Having no liquid phase at normal atmospheric pressure, it sublimes directly from the solid to vapor phase at a temperature of -78.5 °C (-109.3 °F). Dry ice is effective for maintaining products at low temperatures during the period of sublimation.

Cyclic refrigeration: this consists of a refrigeration cycle, where heat is removed from a low-temperature space or source and rejected to a high-temperature sink with the help of external work, and its inverse, the thermodynamic power cycle. In the power cycle, heat is supplied from a high-temperature source to the engine, part of the heat being used to produce work and the rest being rejected to a low-temperature sink. This satisfies the second law of thermodynamics.

A refrigeration cycle describes the changes that take place in the refrigerant as it alternately absorbs and rejects heat as it circulates through a refrigerator. It is also applied to HVACR work, when describing the "process" of refrigerant flow through an HVACR unit, whether it is a packaged or split system.

Heat naturally flows from hot to cold. Work is applied to cool a living space or storage volume by pumping heat from a lower temperature heat source into a higher temperature heat sink. Insulation is used to reduce the work and energy required to achieve and maintain a lower temperature in the cooled space. The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in 1824 as a heat engine.

The most common types of refrigeration systems use the reverse-Rankine vapor-compression refrigeration cycle although absorption heat pumps are used in a minority of applications.

Cyclic refrigeration can be classified as:

1. Vapor cycle, and

2. Gas cycle

Vapor cycle refrigeration can further be classified as:

1. Vapor compression refrigeration

2. Gas absorption refrigeration

Thermoelectric refrigeration: thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. This effect is commonly used in camping and portable coolers and for cooling electronic components and small instruments.

Magnetic refrigeration (or adiabatic demagnetization) is a cooling technology based on the magnetocaloric effect, an intrinsic property of magnetic solids. The refrigerant is often a paramagnetic salt, such as cerium magnesium nitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms.

A strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. A heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off. This increases the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the heat sink.

Because few materials exhibit the required properties at room temperature, applications have so far been limited to cryogenics and research.

Other methods of refrigeration include the Air cycle machine used in aircraft; the Vortex tube used for spot cooling, when compressed air is available; and Thermoacoustic refrigeration using sound waves in a pressurised gas to drive heat transfer and heat exchange.

 

ACTIVE VOCABULARY

refrigeration – охлаждение; замораживание

to remove – удалять, устранять

heat – теплота

to reject – отбрасывать

cooling – охлаждение

artificial - искусственный

to dissipate – рассеивать

to reduce - ослаблять, понижать, сокращать, уменьшать

to accomplish - совершать, выполнять; достигать

mechanical work - механическая работа

heat transfer - теплообмен; теплоотдача; теплопередача;

convection - конвекция

conduction - проводимость

radiation - излучение

non-cyclic – непериодический, нецикличный

cyclic - циклический, цикличный

thermoelectric - термоэлектрический

dry ice - сухой лёд

melting point - точка плавления

to absorb - абсорбировать; поглощать

refrigerant - охлаждающее вещество, охладитель

vapor - пар; пары; испарения;

to supply - поставлять; доставлять

engine - машина, двигатель; мотор

heat source - источник теплоты, тепловой источник

heat sink - теплоотвод, радиатор

insulation – изоляция, изоляционный материал

heat engine - тепловой двигатель

 

VII. Find the Russian equivalents for the English ones:

Second Law of Thermodynamics, subliming dry ice, a cooling agent, thermodynamic power cycle, HVACR, gas absorption refrigeration, thermoelectric cooling, adiabatic demagnetization, Vortex tube, spot cooling.

 

VIII. Find the English equivalents for the Russian ones:

талая вода, передвижная холодильная камера, точка плавления, атмосферное давление, уменьшать, абсорбционный тепловой насос, компрессионное охлаждение испарением холодильного агента, тепловой поток, парамагнитная соль, магнитное поле, теплоёмкость, теплообмен.

 

IX. Translate the following sentences into Russian:

 

1) The process of artificially producing extreme cold temperatures is referred to as cryogenics.

2) Ice owes its effectiveness as a cooling agent to its constant melting point of 0 °C (32 °F).

3) Dry ice is effective for maintaining products at low temperatures during the period of sublimation.

4) Heat is removed from a low-temperature space or source and rejected to a high-temperature sink with the help of external work.

5) Heat is pumped from a lower temperature heat source into a higher temperature heat sink.

6) The most common types of refrigeration systems use the reverse-Rankine vapor-compression refrigeration cycle.

7) Magnetic refrigeration is a cooling technology based on the magnetocaloric effect, an intrinsic property of magnetic solids.

8) The active magnetic dipoles are those of the electron shells of the paramagnetic atoms.

9) A heat sink absorbs the heat released by the refrigerant due to its loss of entropy.

10) Thermoacoustic refrigeration uses sound waves in a pressurised gas to drive heat transfer and heat exchange.

 

X. Fill in the blanks with appropriate words:

1) The term cooling refers generally to any … process.

2) All refrigeration uses the three basic methods of …: convection, conduction, or radiation.

3) Refrigeration can be accomplished by … or by … in the non-cyclic method.

4) Heat is supplied from a high-temperature … to the ….

5) The operating principle of the refrigeration cycle was described mathematically by … in 1824 as ….

6) Thermoelectric cooling uses the … effect.

7) The paramagnetic salt is often a refrigerant by … refrigeration.

8) Thermal contact with … is broken so that the system is insulated, and … is switched off.

9) … is used for spot cooling, when … air is available.

10) Foodstuffs maintained at low temperature have an increased ….

 

XI. Translate into English, using the active vocabulary:

 

1) Охлаждение – это процесс удаления теплоты из закрытого пространства.

2) Холод – это отсутствие тепла.

3) Методы охлаждения можно систематизировать как нецикличный, цикличный и термоэлектрический.

4) Нецикличные методы используются в лабораториях и мастерских для охлаждения небольших размеров.

5) Твёрдая углекислота, известная как сухой лед, используется в качестве охладителя.

6) Изоляционный материал уменьшает энергию, которая требуется для достижения низкой температуры.

7) Абсорбционный тепловой насос используется в меньшем объеме.

8) Эффект Пельтье как правило используют при охлаждении электронных компонентов и небольшого оборудования.

9) Сильное магнитное поле направляется на охладитель.

10) Когда магнитное поле отключается, это повышает теплоёмкость охладителя.

 

XII. Answer the questions:

 

1) What is refrigeration?

2) What process is cooling? What is cryogenics?

3) What form of work must be performed to reduce a temperature?

4) What methods of heat transfer does refrigeration use?

5) Where is non-cyclic refrigeration used? What is its refrigerant?

6) How does a refrigeration cycle work?

7) What is insulation used to?

8) How can cyclic refrigeration be classified?

9) What kinds of vapor cycle refrigeration do you know?

10) What does thermoelectric refrigeration use? Where is it used?

11) What is magnetic refrigeration based on? How does it work?

12) What other methods of refrigeration do you know?

 

XIII. Fulfill the table using information from the text:

 

Method	Refrigerant	How does it work?	Application

 

XIV. Tell in short about methods of refrigeration.

 

UNIT 2

 

I. Read and translate the text:

Boiling point

The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid. A liquid in a vacuum environment has a lower boiling point than when the liquid is at atmospheric pressure. And a liquid in a high pressure environment has a higher boiling point than when the liquid is at atmospheric pressure. In other words, all liquids have an infinite number of boiling points.

The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the special case at which the vapor pressure of the liquid equals the ambient atmospheric pressure. At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and lift the liquid to form bubbles inside the bulk of the liquid.

The heat of vaporization is the amount of heat required to convert or vaporize a saturated liquid (i.e., a liquid at its boiling point) into a vapor.

Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation. Evaporation is a surface phenomenon in which molecules located near the vapor/liquid surface escape into the vapor phase. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, resulting in the formation of vapor bubbles within the liquid.

A saturated liquid contains as much thermal energy as it can without boiling (or conversely a saturated vapor contains as little thermal energy as it can without condensing).

Saturation temperature means boiling point. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase change.

If the pressure in a system remains constant (isobaric), a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy (heat) is removed. Similarly, a liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied.

The boiling point corresponds to the temperature at which the vapor pressure of the liquid equals the surrounding environmental pressure. Thus, the boiling point is dependent on the pressure. Usually, boiling points are published with respect to atmospheric pressure (101.325 kilopascals or 1 atm). At higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased pressure up to the critical point, where the gas and liquid properties become identical. The boiling point cannot be increased beyond the critical point. Likewise, the boiling point decreases with decreasing pressure until the triple point is reached. The boiling point cannot be reduced below the triple point.

Saturation Pressure, or vapor point, is the pressure for a corresponding saturation temperature at which a liquid boils into its vapor phase. Saturation pressure and saturation temperature have a direct relationship: as saturation pressure is increased so is saturation temperature.

If the temperature in a system remains constant (an isothermal system), vapor at saturation pressure and temperature will begin to condense into its liquid phase as the system pressure is increased. Similarly, a liquid at saturation pressure and temperature will tend to flash into its vapor phase as system pressure is decreased.

Note: The boiling point of water is 100 °C (212 °F) at standard pressure. On top of Mount Everest the pressure is about 260 mbar (26 kPa) so the boiling point of water is 69 °C. (156.2 °F). The normal boiling point of water is 99.97 degrees Celsius at a pressure of 1 atm (i.e., 101.325 kPa).

The element with the lowest boiling point is helium. Both the boiling points of rhenium and tungsten exceed 5000 K at standard pressure. Due to the experimental difficulty of precisely measuring extreme temperatures without bias, there is some discrepancy in the literature as to whether tungsten or rhenium has the higher boiling point.

 

ACTIVE VOCABULARY

boiling point – точка кипения

vapor pressure – давление пара

to equal – быть одинаковым, равным

atmospheric pressure – атмосферное давление

infinite – бесконечный, бесчисленный

sufficient – достаточный

to overcome (overcame, overcome) – побороть, победить

heat of vaporization – теплота испарения, теплота парообразования

to convert – преобразовывать; превращать

to contain – содержать в себе, включать

saturated vapor – насыщенный пар

saturation temperature – температура насыщения

saturation pressure – давление насыщения

vapor phase – паровая фаза

to remain – оставаться

constant – неизменный, устойчивый, константный

to correspond (to) – соответствовать; согласовываться, соотноситься

dependent on – обусловленный, зависящий (от обстоятельств)

with respect to – относительно, по отношению к

identical – такой же, одинаковый, идентичный

to reduce – понижать, уменьшать

isothermal – изотермический, изотермичный, равнотемпературный

helium – гелий

rhenium – рений

tungsten – вольфрам

to exceed – превышать; выходить за пределы

without bias – объективно

 

II. Find the Russian equivalents for the English ones:

saturated liquid, environmental pressure, discrepancy, a phase change, a liquid phase, atmospheric boiling point, the triple point, ambient atmospheric pressure, vapor point

 

III. Find the English equivalents for the Russian ones:

непосредственная связь, парообразная фаза, нормальное давление, точка кипения жидкости, насыщенный пар, бесконечное число, поверхностное явление, критическая точка

 

IV. Say whether these sentences are True or False:

1) A saturated vapor contains as little thermal energy as it can with boiling.

2) A liquid in a high pressure environment has a higher boiling point than when the liquid is at atmospheric pressure.

3) A vapor at saturation temperature and pressure will begin to condense into its liquid phase as thermal energy is removed.

4) At saturation pressure a vapor is converted into its liquid phase.