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Министерство образования и науки Российской Федерации
Государственное образовательное учреждение
высшего профессионального образования
Санкт-Петербургский государственный университет
низкотемпературных и пищевых технологий
Кафедра иностранных языков
АНГЛИЙСКИЙ ЯЗЫК
Методические указания
по подготовке к контрольным работам 5 и 6
для студентов 2-го курса всех специальностей
заочной формы обучения
Санкт-Петербург
2010
УДК 811.111
Васильева Л.А., Домбровская А.В. Английский язык: Метод. указания по подготовке к контрольным работам 5 и 6 для студентов 2-го курса всех специальностей заочной формы обучения. – СПб.: СПбГУНиПТ, 2010. – 41 с.
Приведены технические тексты для чтения студентами 2-го курса всех специальностей с целью расширения словарного запаса и подготовки к выпол-нению контрольных работ по английскому языку.
Рецензент
Канд. пед. наук, проф. Н.А. Дмитренко
Рекомендованы к изданию редакционно-издательским советом уни-верситета
Санкт-Петербургский государственный
университет низкотемпературных
и пищевых технологий, 2010
Методические указания предназначены для студентов-заоч-ников 2-го курса, изучающих английский язык, и состоят из технических текстов для чтения студентами специальностей 140500, 140400, 140504, 190600, 190603, 240300, 240902, 260200, 260202, 260204, 260300, 260301, 260302, 260303, 260500, 260504.
Студентам рекомендуется прочитать и устно перевести тексты с помощью англо-русского словаря и словаря терминов, следующего за текстами.
Незнакомые слова следует выписывать в специальную тетрадь и стараться их запомнить. За полный курс обучения активный словарный запас студента должен составлять 900–1000 лексических единиц.
Контрольная работа № 5 выполняется после перевода текстов по специальности широкого профиля (с. 4–14 настоящих методических указаний).
Контрольная работа № 6 – после перевода текстов на с. 15– 20 для студентов специальнос ти 140500, 140400, 140504, 190600, 190603, а на с. 21–25 – для студентов специальностей 240300, 240902, 260200, 260202, 260204, 260300, 260301, 260302, 260303, 260500, 260504.
Для расширения словарного запаса студентам всех специальностей рекомендуется прочитать Приложение, содержащее дополнительные тексты по истории искусственного охлаждения.
Heat
Heat is a form of energy. This is evident from the fact that heat can be converted into other forms of energy and that other forms of energy can be converted into heat.
Matter and Molecules
Everything that has mass or occupies space – all matter – is composed of molecules. The molecule is the smallest stable particle of matter into which a particular substance can be subdivided and still retain the identity of the original substance. For example, a grain of table salt (NaCl) may be broken down into individual molecules, and each molecule will be a molecule of salt, the original substance. However, all molecules are made up of atoms, so that it is possible to further subdivide a molecule of salt into its component atoms. A molecule of salt is made up of one atom of sodium and one atom of chlorine. Therefore, if a molecule of salt is divided into its atoms, the atoms will not be atoms of salt, the original substance, but atoms of two entirely different substances, one of sodium and one of chlorine. It is assumed that the molecules that make up a substance are held together by forces of mutual attraction known as cohesion. These forces of attraction that the molecules have for each other may be likened to the attraction that exists between unlike electrical charges or between unlike magnetic poles. However, despite the mutual attraction that exists between the molecules and the resulting influence that each molecule has upon the others, the molecules are not tightly packed together. There is a certain amount of space between them, and they are relatively free to move about. The molecules are further assumed to be in a state of rapid and constant vibration or motion, the rate and extent of the vibration or movement being determined by the amount of energy they possess.
Internal Energy
A body has external mechanical energy because of its velocity and/or its position or configuration. A body also has internal energy resulting from the velocity and position or configuration of the molecules that make up the body.
The molecules of any material may possess both kinetic and potential energy. The total internal energy of a material is the sum of its internal kinetic and potential energy.
Internal Kinetic Energy
Internal kinetic energy is the energy of molecular motion or velocity. When energy passing into a substance increases the motion or velocity of the molecules, the internal kinetic energy of the substance is increased, and this increase is reflected by an increase in the temperature of the substance. Conversely, if the internal kinetic energy of the substance is diminished by the loss of energy, the motion of the molecules will decrease, and the temperature will decrease accordingly.
It is evident from the foregoing that the temperature of a body is an index of the average velocity of the molecules that make up the body. According to the kinetic theory, if the loss of energy from a body continued until the internal kinetic energy was reduced to zero, the temperature of the body would drop to absolute zero (– 459.7 ºF), and the molecules would be come completely motionless.
States of Matter
Matter is known to exist in three different phases or states of aggregation: as a solid, as a liquid, or as a vapor or gas. For example, water is a liquid, but this same substance can exist аs ice, which is a solid, or as steam, which is a vapor or a gas.
The Effect of Heat on the State of Aggregation
Many materials, under the proper conditions of pressure and temperature, can exist in any and all of the three physical states of matter. It will be shown presently that the amount of energy that molecules of a material have determines not only the temperature of the material but also which of the three physical states the material will assume at any parti cular time. In other words, the addition or removal of energy can bring about a change in the physical state of the material as well as a change in its temperature.
That energy can bring about a change in the physical state of a material is evident from the fact that many materials, such as metals, will become molten if sufficient heat is applied. The phenomenon of melting ice and boiling water is familiar to everyone. Each of these changes in the physical state is brought about by the addition of energy.
Internal Potential Energy
Internal potential energy is the energy of molecular separation or configuration. It is the energy that molecules have as a result of their position in relation to one another. The greater the degree of molecular separation, the greater is the internal potential energy.
When a material expands or changes its physical state with the addition of energy, a rearrangement of the molecules takes place which increases the distance between them. Inasmuch as the molecules are attracted to one another by forces that tend to pull them together, internal work must be done in order to further separate the molecules against these attractive forces. An amount of energy equal to the amount of internal work done must be supplied to the material. This energy is set up in the material as an increase in the internal poten tial energy, and it is this "stored" energy that is accounted for by the increase in the mean distance between the molecules.
It is important to understand that in this instance the energy passing into the material has no effect on molecular velocity (internal kinetic energy); only the degree of molecular separation (the internal potential energy) is affected.
The Solid Phase
A material in the solid phase has a relatively small amount of internal potential energy. The molecules of the material are rather closely bound together by each other's attractive forces and by the force of gravity. Material in the solid phase has a rather rigid molecular structure in which the position of each molecule is more or less fixed, and the mo tion of the molecules is limited to a vibratory type of movement which, depending on the amount of internal kinetic energy the molecules possess, may be either slow or rapid.
Because of its rigid molecular structure, a solid tends to retain both its size and its shape. A solid is practically non-compressible and will offer considerable resistance to any effort to change its shape.
The Liquid Phase
The molecules of a material in the liquid phase have more energy than those of a material in the solid phase, and they are not as closely bound together. Their greater energy allows them to overcome each other's attractive forces to some extent and to have more freedom to move about. They are free to move over and around one another in such a way that the material is said to "flow". Although a liquid is practically non-compressible and will retain its size, because of its fluid molecular structure, it will not retain its shape but will assume the shape of any containing vessel.
The Vapor or Gaseous Phase
The molecules of a material in the gaseous phase have an even greater amount of energy than those in the liquid phase. They have sufficient energy to overcome all restraining forces. They are no longer bound by each other's attractive forces, nor are they bound by the force of gravity. Consequently, they fly about at high velocities, continually colliding with each other and with the walls of the container. For this reason, a gas will retain neither its size nor its shape. It is readily compressible and completely fills any containing vessel. Furthermore, if the gas is not stored in a sealed container, it will escape from the container and be diffused into the surrounding air.
Temperature
Temperature is a property of matter. It is a measure of the level of the thermal pressure of a body. A high temperature indicates a high level of thermal pressure, and the body is said to be hot. Likewise, a low temperature indicates a low level of thermal pressure, and the body is said to be cold. It has already been shown that temperature is a function of the internal kinetic energy and, as such, is an index of the average molecular velocity.
Thermometers
The most frequently used instrument for measuring temperature is the thermometer. The operation of most thermometers depends upon the property of a liquid to expand or contract as its temperature is increased or decreased respectively. Because of their low freezing temperatures and relatively constant coefficients of expansion, alcohol and mercury are the liquids most frequently used in thermometers. The mercury thermometer is the more accurate of the two because its coefficient of expansion is more constant through a greater temperature range than is that of alcohol. However, mercury thermometers have the disadvantage of being more expensive and more difficult to read. Alcohol is cheaper and can be colored for easy visibility.
Temperature scales in common use today are the Celsius and Fahrenheit scales. The point at which water freezes under standard barometric pressure is taken as the arbitrary zero point of the Celsius scale, and the point at which water boils under standard barometric pressure is designated as 100. The distance on the scale between these two points is divided into 100 equal units called degrees, so that the difference between the freezing and boiling points of water on the Celsius scale is 100. Water freezes at 0 o C and boils at 100 o C.
Although there is some disagreement as to the actual method used by Fahrenheit in designing the first temperature scale, he arrived at it by means similar to those described for the Celsius scale. On the Fahrenheit scale, the point at which water freezes is marked as 32, and the point at which water boils is 212. Thus, there are 180 units between the freezing and boiling points of water.
The zero or reference point on the Fahrenheit scale is placed 32 units or degrees below the freezing point of water.
It is assumed to represent the lowest temperature Fahrenheit could achieve with a mixture of ammonium chloride and snow.
Temperature readings on one scale can be conveyed to readings on the other scale by using the following equations:
oF = 9/5 (oC + 32)
oC = 5/9 (oF – 32)
It should be noted that the difference between the freezing and boiling points of water on the Fahrenheit scale is 180 degrees, whereas the difference between these two points on the Celsius scale is 100 degrees which are equivalent to 180 Fahrenheit degrees. This estab lishes a relationship such that 1oC equals 9/5 oF (1.8 oF) and 1 oF equals 5/9 oC (0.555 oC ). Since 0 on the Fahrenheit scale is 32 oF below the freezing point of water, it is necessary to add 32 oF to the Fahrenheit equivalent after converting from Celsius. Likewise, it is necessary to subtract 32 oF from a Fahrenheit reading before converting it to Celsius.
Absolute Temperature
Temperature readings taken from either the Fahrenheit or Celsius scales are based on arbitrarily selected zero points that, as has been shown, are not even the same for the two scales. When it is desired to know only the change in tem perature that occurs during a process or the temperature of a substance in relation to some known reference point, such readings are adequate. However, when temperature readings are to be applied in equations dealing with certain fundamental laws, it is necessary to use temperature readings whose reference point is the true or absolute zero of temperature. Experiment has indicated that such a point, known as absolute zero, exists at approximately –460 ºF which is equal to –273 ºC.
Temperature readings determined from absolute zero are designated as absolute temperatures and may be in either Fahrenheit or Celsius degrees. A temperature reading on the Fahrenheit scale can be converted to absolute temperature by adding 460 ºF to the Fahrenheit reading. The resulting temperature is in degrees Rankine (ºR).
Likewise, Celsius temperature can be converted to absolute temperatures by adding 273 ºC to the Celsius reading. The resulting temperature is stated in degrees Kelvin (K).
In converting to and from absolute temperatures, the following relationships are used:
oR = oF + 460
oF = oR – 460
K = oC +273
oC = K – 273
Direction and Rate of Heat Transfer
Heat will pass from one body to another when and only when a difference in temperature exists between the two bodies. When a body is in thermal equilibrium with (i.e., at the same temperature as) its surroundings, there can be no transfer of energy as heat between the body and its surroun dings.
Heat transfer is always from a region of high tempe rature to a region of lower temperature (from a warm body to a colder body) and never in the opposite direction. Since heat is energy and consequently is not destroyed or used up in any process, the heat energy that leaves one body must раss into and be absorbed by another body whose temperature is lower than that of the body losing the energy. The rate of heat transfer is always proportional to the difference in temperature causing transfer.
Methods of Heat Transfer
The transfer of energy as heat is known to occur in three ways:
(1) by conduction, (2) by convection, and (3) by radiation.
Conduction
Heat transfer by conduction occurs when energy is transmitted by direct contact between the molecules of a single body or between the molecules of two or more bodies in good thermal contact with each other. In either case, the heated molecules communicate their energy to the other molecules immediately adjacent to them. The transfer of energy from molecule to molecule by conduction is similar to that which takes place between the balls on a billiard table, wherein all or some part of the energy of motion of one ball is transmitted at the moment of impact to the other balls that are struck.
When one end of a metal rod is heated over a flame, some of the heat energy from the heated end of the rod will flow by conduction from molecule to molecule through the rod to the cooler end. As the molecules at the heated end of the rod absorb energy from the flame, their energy increases, and they move faster and through a greater distance. The increased energy of the heated molecules causes them to strike against the molecules immediately adjacent to them. At the moment of impact and because of it, the faster moving molecules transmit some of their energy to their slower moving neighbors, so that they too begin to move more rapidly. In this manner, energy passes from molecule to molecule from the heated end of the rod to the cooler end. However, in no case would it be possible for the molecules furthest from the heat source to have more energy than those at the heated end.
As heat passes through the metal rod, the air immediately surrounding the rod is also heated by conduction. The rapidly vibrating particles of the heated rod strike against the molecules of air that are in contact with the rod. The energy so imparted to the air molecules causes them to move about at a higher rate and communicate their energy to other nearby air molecules. Thus, some of the heat supplied to the metal rod is conducted to and carried away by the sur rounding air.
If the heat supply to the rod is interrupted, heat will continue to be carried away from the rod by the air surrounding the rod until the temperature of the rod drops to that of the air. When this occurs, there will be no tem perature differential, the system will be in equilibrium, and no heat will be transferred.
The rate of heat transfer by conduction, as previously stated, is in direct proportion to the difference in tem perature between the high and low temperature parts. However, all materials do not conduct heat at the same rate. Some materials, such as metals, conduct heat very readily, whereas others, such as glass, wood, and cork, offer con siderable resistance to the conduction of heat. Therefore, for any given temperature difference, the rate of heat flow by conduction through different materials of the same length and cross section will vary with the particular ability of the various materials to conduct heat. The relative capacity of a material to conduct heat is known as its con ductivity. Materials that are good conductors of heat have a high conductivity, whereas materials that are poor conductors have a low conductivity and are used as heat insulators.
In general, solids are better conductors of heat than liquids, and liquids are better conductors than gases. This is accounted for by the difference in the molecular structure. Since the molecules of a gas are widely separated, the transfer of heat by conduction, that is, by direct contact between the molecules, is difficult.
Convection
Heat transfer by convection occurs when heat moves from one place to another bу means of currents that are set up within some fluid medium. These currents are known as convection currents and result from the change in density that is brought about by the expansion of the heated portion of the fluid.
When any portion of a fluid is heated, it expands, and its volume per unit of mass increases. Thus the heated portion becomes lighter, rises to the top, and is immediately replaced by a cooler, heavier portion of the fluid. For example, assume that a tank of water is heated at the bottom in the center. The heat from the flame is conducted through the metal bottom of the tank to the water inside. As the water adjacent to the heat source absorbs heat, its temperature increases, and it expands. The heated portion of the water, being lighter than the surrounding water, rises to the top and is replaced by the cooler one, denser water pushing in from the sides. As this new portion of water becomes heated, it too rises to the top and is replaced by cooler water from the sides. As this sequence continues, the heat is distributed throughout the entire mass of the water by means of the con vection currents established within the mass.
Room heated by natural convection
Warm air currents, such as those that occur over stoves and other hot bodies, are familiar to everyone. Figure 2 illustrates how convection currents are utilized to carry heat to all parts of a heated space.
Radiation
Heat transfer by radiation occurs in the form of a wave motion similar to light waves wherein the energy is transmit ted from one body to another without the need for inter vening matter. Heat energy transmitted by wave motion is called radiant energy.
It is assumed that the molecules of a body are in rapid vibration and that this vibration sets up a wave motion in the space surrounding the body. Thus the internal molecular energy of the body is converted into radiant energy waves. When these energy waves are intercepted by another body of matter, they are absorbed by that body and are converted into its internal energy.
The earth receives heat from the sun by radiation. The energy of the sun's molecular vibration is imparted in the form of radiant energy waves to the space surrounding the sun. The energy waves travel across billions of miles of space and impress their energy upon the earth and upon any other material bodies that intercept their path. The radiant energy is absorbed and transformed into internal energy, so that the vibratory motion of the hot body (the sun) is reproduced in the cooler body (the earth).
All materials give off and absorb heat in the form of radiant energy. Any time the temperature of a body is greater than that of its surroundings, it will give off more heat by radiation than it absorbs. Therefore, it loses energy to its surroundings, and its internal energy decreases. If the temperature of the body is below that of its sur roundings, it absorbs more radiant energy than it loses, and its internal energy increases. When no temperature dif ference exists, the energy exchange is in equilibrium, and the body neither gains nor loses energy.
Heat transfer through a vacuum is impossible by either conduction or convection, since these processes, by their very nature, require that matter be the transmitting media. Radiant energy, on the other hand, is not dependent upon matter as a medium of transfer and therefore can be trans mitted through a vacuum. Furthermore, when radiant energy is transferred from a hot body to a cold through some inter vening media such as air, the temperature of the intervening media is unaffected by the passage of the radiant energy. For example, heat is radiated from a "warm" wall to a "cold" wall through the intervening air without having any appreciable effect upon the temperature of the air. Since the molecules of the air are relatively few and widely separated, the waves of radiant energy can easily pass between them, so that only a very small part of the radiant energy is intercepted and absorbed by .the molecules of the air. By far, the greater portion of the radiant energy falls upon and is absorbed by the solid wall whose molecular structure is much more compact and substantial.
Heat waves are very similar to light waves, differing from them only in length and frequency, light waves are radiant energy waves of such length as to be visible to the human eye. Thus, light waves are visible heat waves. Whether heat waves are visible or invisible depends on the temperature of the radiating body, for example, when metal is heated to a sufficiently high temperature, it will "glow", that is emit visible heat waves (light).
When radiant energy waves, either visible or invisible, strike a material body, they may be reflected, refracted, or absorbed by it, or they may pass through it to some other substance beyond.
The amount of radiant energy that will pass through a material depends on the degree of transparency. A highly transparent material, such as clear glass or air, will allow most of the radiant energy to pass through to the materials beyond, whereas opaque materials, such as wood, metal, and cork, cannot be penetrated by radiant energy waves, and none will pass through.
The amount of radiant energy that is either reflected or absorbed by a material depends on the nature of the material’s surface, that is, its texture and its color. Materials with a light-colored, highly polished surface, such as a mirror, reflect a maximum of radiant energy, whereas materials with rough, dull, dark surfaces will absorb the minimum amount of radiant energy.
British Thermal Unit
The quantity of heat energy is measured in British thermal units (Btu). The British thermal unit is defined as the quantity of heat required to change the temperature of 1 lb. of water 1°F. Added to 1 lb of water, 1 Btu will increase the temperature of the water 1oF. Similarly, re moving 1 Btu from 1 lb. of water will lower the temperature of the water 1oF .
Since the quantity of heat required to change the temperature of water 1°F varies slightly with the temperature range at which the change occurs, the Btu is more accurately defined as l/180th of the quantity of heat required to raise the temperature of 1 lb of water from its freezing tempe rature (32°F) to its boiling temperature (212oF), a tempe rature change of 180°F.
Specific Heat
The specific heat of any substance is the quantity of energy in Btu required to change the temperature of a 1 lb. mass 1°F. For example, the specific heat of brass is 0.089 Btu/lb °F. This means that 0.089 Btu of heat energy must be supplied to 1 lb. of brass to increase the temperature of the brass 1oF. Conversely, 0.089 Btu of energy must be given up by the brass to reduce the temperature of the brass 1oF. Notice that the specific heat of water, by definition of the Btu, is fixed at one Btu per pound per degree Fahrenheit (1 Btu/lb °F).
Although the specific heat of any substance varies with the temperature range for most liquids and solids the change is small, and the specific heat can be assumed to be constant for most routine calculations. However, the specific heat of a substance changes significantly with a change in phase. For example, the specific heat of water is 1 Btu/lb oF, whereas the specific heat of ice is 0.5 Btu/lb F°.
The specific heat of any gas will take many different values depending on the conditions under which the temperature of the gas is caused or allowed to change.
Sensible Heat and Latent Heat
Heat energy transferred to or from a substance can bring about a change in the phase of the substance as well as a change in its temperature. As a matter of convenience, heat energy is divided into two types or categories, de pending on which of these two effects the heat energy has on the substance that absorbs or gives up the energy. Heat energy that causes or accompanies a change in the temperature of a substance is called sensible heat, whereas heat energy that causes or accompanies a change in the phase of a substance is known as latent heat.
In progressing up the temperature scale, most materials will undergo two changes in the state of aggregation. First, they go from the solid phase to the liquid phase, and then, as the temperature of the liquid is further increased to a level beyond which it cannot exist as a liquid, the liquid will change into a vapor. When the change occurs between the solid and liquid phases in either direction, the latent heat involved is known as the latent heat of fusion. When the change occurs between the liquid and vapor phases in either direction, the latent heat involved is called the latent heat of vaporization.
Refrigeration
In general, refrigeration is defined as any process of heat removal. More specifically, refrigeration is defined as the branch of science that deals with the process of reducing and maintaining the temperature of a space or material below the temperature of the surroundings.
To accomplish this, heat must be removed from the body being refrigerated and transferred to another body whose temperature is below that of the refrigerated body. Since the heat removed from the refrigerated body is transferred to another body, it is evident that refrigerating and heat ing are actually opposite ends of the same process.
Need for Thermal Insulation
Since heat will always migrate from a region of high tempe rature to a region of lower temperature, there is always a continuous flow of heat into the refrigerated region from the warmer surroundings. To limit the flow of heat into the refrigerated region to some practical minimum, it is usually necessary to isolate the region from its surroundings with a good heat-insulating material.
The Refrigeration Load
The rate at which heat must be removed from the refrigerated space or material in order to produce and maintain the desired temperature conditions is called the refrigeration load, the cooling load, or the heat load. In most refrigeration applica tions, the total cooling load on the refrigerating equipment is the sum of the heat gains from several different sources: (1) the heat transmitted by conduction through the insulated walls, (2) the heat that must be removed from the warm air that enters the space through opening and closing doors, (3) the heat that must be removed from the refrigerated product to reduce the temperature, and (4) the heat given off by people working in the space and by motors, lights, and other heat-producing equipment operating in the space.
The Refrigerating Agent
In any refrigerating process, the substance employed as the heat absorber or cooling agent is called the refrigerant.
All cooling processes may be classified as either sensible or latent according to the effect the absorbed heat has upon the refrigerant. When the absorbed heat causes an increase in the temperature of the refrigerant, the cooling process is said to be sensible, whereas when the absorbed heat causes a change in the physical state of the refrigerant (either melt ing or vaporizing), the cooling process is said to be latent. With either process, if the refrigerating effect is to be con tinuous, the temperature of the refrigerant must be maintained continuously below that of the space or material being refri gerated.
It is both possible and practical to achieve continuous re frigeration with a sensible cooling process provided that the refrigerant is continuously chilled and recirculated through the refrigerated space.
Latent cooling mау be accomplished, with either solid or li quid refrigerants. The solid refrigerants most frequently em ployed are ice and solid carbon dioxide (dry ice). Ice, of course, melts into the liquid phase at 32oF, whereas solid car bon dioxide sublimes directly into the vapor phase at a tempe rature of –109 oF under standard atmospheric pressure.
Ice Refrigeration
Melting ice has been used successfully for many years as a re frigerant. Not too many years ago ice was the only cooling agent available for use in domestic and small commercial refri gerators.
In a typical ice refrigerator the heat entering the refrige rated space from all the various sources reaches the melting ice primarily by convection currents set up in the air of the refrigerated space. The air in contact with warm product and walls of the space is heated by heat conducted to it from these materials. As the air is warmed it expands and rises to the top of the space carrying the heat with it to the ice compartment. In passing over the ice the air is cooled as heat is conducted from the air to ice. On cooling the air becomes denser and falls back into the storage space, absorbs more heat and the cycle is repeated.
The air carrying the heat from the warm walls and stored product to the melting ice acts as a heat transfer agent. To assure adequate air circulation within the refrigerated space, the ice should be located near the top of the refrigerator and proper baffling should be installed to provide direct and unrestricted paths of air flow. A drip pan must bе located beneath the ice to collect the water that results from the melting.
Ice has certain disadvantages which tend to limit its usefulness as a refrigerant. For instance, with ice it is not possible to obtain the low temperatures required in many refrigeration applications. Ordinarily, 32oF is the minimum temperature obtainable through melting of ice alone. In some cases, the melting temperature of the ice can be lowered to approximately 0°F by adding sodium chloride or calcium chlo ride to produce a freezing mixture. Some of the other more obvious disadvantages of ice are the necessity of frequently replenishing the supply, a practice that is neither convenient nor economical, and the problem of disposing of the water resulting from the melting of the ice.
Another less obvious, but more important, disadvantage of employing ice as a refrigerant is the difficulty experienced in controlling the rate of refrigeration, which in turn makes it difficult to maintain the desired low temperature level within the refrigerated space. Since the rate at which the ice absorbs heat is directly proportional to the surface area of the ice and to the temperature difference between the space temperature and the melting temperature of the ice, the rate of heat absorption by the ice diminishes as the surface area of the ice is diminished by the melting process. Naturally, when the refrigerating rate deminishes to the point that heat is not being removed at the same rate that it is accumulating in the space from the various sources, the temperature of the space will increase.
Despite its disadvantages, ice is preferable to mechani cal refrigeration in some applications. Fresh vegetables, fish, and poultry are often packed and shipped in cracked ice to prevent dehydration and to preserve appearance. Al so, ice has tremendous eye appeal and can be used to consi derable advantage in the displaying and serving of certain foods such as salads and cocktails and in chilling beverages
Liquid Refrigerants
The ability of liquids to absorb enormous quantities of heat as they vaporize is the basis of the modern mechanical refri gerating system. As refrigerants, vaporizing liquids have a number of advantages over melting solids in that the vapori zing process is more easily controlled; that is, the refri gerating effect can be started and stopped at will, the rate of cooling can be governed by controlling the pressure at which the liquid vaporizes. Moreover, the vapor can be readi ly collected and condensed back into the liquid state so that the same liquid can be used over and over again to provide a continuous supply of liquid for vaporization.
Until now, in discussing the various properties of fluids, water, because of its familiarity, has been used in most examples. However, because of its relatively high saturation temperature, and for other reasons, water is not suitable for use as a refrigerant in the vapor-compression cycle. In order to vaporize at temperatures low enough to satisfy most refrigeration requirements, water would have to vaporize under very low pressures, which are difficult to produce and maintain eco nomically.
There are numerous other fluids which have lower saturation temperatures than water at the same pressure. However, many of these fluids have other properties that render them unsuitable for use as refrigerants. Actually, only a relatively few fluids have properties that make them desirable as refrigerants, and most of these have been compounded specially for that purpose.
There is no one refrigerant that is best suited for all the different applications and operating conditions. For any specific application the refrigerant selected should be the one whose properties most closely fit the particular requirements of the application.
Of all the fluids now in use as refrigerants, the one fluid that most nearly meets all the qualifications of the ideal general-purpose refrigerant is a fluorinated hydro carbon of the methane series having the chemical name dichlorodifluoromethane (CCl2F2). It is one of the groups of refrigerants introduced to the industry under the trade name of Freons. To avoid the confusion inherent in the use of proprietary of chemical names, this compound is now referred to as Refrigerant 12.
The Ideal Refrigerant
Generally speaking, a refrigerant is any body or substance which acts as a cooling agent by absorbing heat from another body or substance. With regard to the vapor-compression cycle, the refrigerant is the working fluid of the cycle which al ternately vaporizes and condenses as it absorbs and gives off heat, respectively. To be suitable for use as a refrigerant in the vapor-compression cycle, a fluid should possess cer tain chemical, physical, and thermodynamic properties that make it both safe and economical to use.
It should be recognized at the onset that there is no "ide al" refrigerant and that, because of the wide differences in the conditions and requirements of the various applications, there is no one refrigerant that is universally suitable for all applications. Hence, a refrigerant approaches the "ideal" only to the extent that its properties meet the conditions and requirements of the application for which it is to be used.
There is a number of fluids having properties which ren der them suitable for use as refrigerants. However, it will be shown presently that only a few of the more desirable ones are actually employed as such. Some, used extensively as refrigerants in the past, have been discarded as more suitable fluids were developed. Others, still in the deve lopment stage, show promise for the future.
Safe Properties
Ordinarily, the safe properties of the refrigerant are the prime consideration in the selection of a refrigerant. It is for this reason that some fluids, which otherwise are highly desirable as refrigerants, find only limited use as such. The more prominent of these are ammonia and some of the hy drocarbons.
To be suitable for use as a refrigerant, a fluid should be chemically inert to the extent that it is nonflammable, nonexplosive, and nontoxic both in the pure state and when mixed in any proportions with air. Too, the fluid should not react with the lubricating oil or with any material nor mally used in the construction of refrigerating equipment. Nor should it react unfavorably with moisture which despite stringent precautions is usually present at least to some degree in all refrigerating systems. Furthermore, it is de sirable that the fluid be of such a nature that it will not contaminate in any way foodstuff or other stored products in the event that a leak develops in the system.
Toxicity
All fluids other than air are toxic in the sense that they will cause suffocation when in concentration large enough to preclude sufficient oxygen to sustain life. Various re frigerants are separated into six groups according to their degree of toxicity. Those falling into the highly toxic group are capable of causing death or serious injury in re latively small concentrations and short exposure periods. It should be pointed out that some refrigerants, although nontoxic when mixed with air in their normal state, are sub ject to decomposition when they come in contact with an open flame or an electrical heating element. The products of de composition thus formed are highly toxic and capable of caus ing harmful effects in small concentrations and on short ex posure.
Flammability and Explosiveness
Most of the refrigerants in common use are entirely nonflam mable and nonexplosive. Ammonia is slightly flammable and explosive when mixed in rather exact proportions with air. However with reasonable precautions the hazard involved in using ammonia as a refrigerant is negligible.
Straight hydrocarbons, on the other hand, are highly flammable and explosive, and their use as refrigerants except in special applications and under the control of experienced oper ating personnel is not usually permissible. Because of their excellent thermal properties, the straight hydrocarbons are frequently employed in ultra low temperature applications.
Economic Considerations
Naturally, the critical temperature and pressure of the refrigerant must be above the maximum temperature and pressure which will be encountered in the system. Likewise, the freezing point of the refrigerant must be safely below the minimum temperature to be obtained in the cycle. These factors are particularly important in selecting a refrigerant for a low temperature application.
Since the power required per unit of refrigerating capa city is very nearly the same for all the refrigerants in com mon use, efficiency and economy of operation are not usually deciding factors in the selection of the refrigerant. More important are those properties which tend to reducing the size, weight, and initial cost of the refrigerating equip ment and which permit automatic operation and a minimum of maintenance. The cost and the availability of the refrig erant itself are also important considerations in the selec tion of a refrigerant.
Early Refrigerants
In earlier days when mechanical refrigeration was limited to a few large applications, ammonia and carbon dioxide were practically the only refrigerants available. Later, with the development of small, automatic domestic and commercial units, refrigerants such as sulfur dioxide and methyl chloride came into use, along with methylene chloride, which was developed for use with centrifugal compressors. Methylene chloride and carbon dioxide, because of their safe properties, were extensively used in large air condi tioning applications.
With the exception of ammonia, all these refrigerants have fallen into disuse and are found only in some of the older installations, having been discarded in favor of the more suitable fluorocarbon refrigerants as the latter were developed. The fluorocarbons are practically the only refrigerants in extensive use at the present time. Again, an exception to this is ammonia which, because of its excellent thermal properties, is still widely used in such installations as ice plants, skating rinks, etc. A few other refrigerants also find limited use in special applications.
Food Preservation
The preservation of perishable commodities, particularly foodstuffs, is one of the most common uses of mechanical refrigeration.
At the present time, food preservation is more important than ever before in man's history. Today's large urban population requires tremendous quantities of food, which for the most part must be produced and processed in outlying areas. Naturally, these foodstuffs must be kept in a preserved condition during transit and subsequent storage until they are finally consumed. This may be a matter of hours, days, weeks, months, or even years in some cases. Too, many products, particularly fruit and vegetables, are seasonal. Since they are produced only during certain seasons of the year, they must be stored and preserved if they are to be made available the year round.
As a matter of life or death, the preservation of food has long been one of our most pressing problems. Almost from the very beginning of our existence on earth, it became necessary for us to find ways of preserving food during seasons of abundance in order to live through seasons of scarcity. It is only natural, then, that man should discover and develop such methods of food preser vation as drying, smoking, pickling, and salting long before he had any knowledge of the causes of food spoilage.
These rather primitive methods are still widely used today, not only in backward societies where no other means are available but also in the most modern societies. For instance, millions of pounds of dehydrated (dried) fruit, milk, eggs, fish, meat, potatoes, etc. are consumed each year, along with huge quantities of smoked, pickled, and salted products, such as ham, bacon, and sausage, to name only a few. However, although these older methods are entirely adequate for the preservation of certain types of food, and often produce very unusual and tasty products which would not otherwise be available, they nonetheless have inherent disadvantages which limit their usefulness. Since they usually bring about rather severe changes in appearance and taste, which in many cases are objectionable, they are not universally adaptable for the preservation of all types of food products. Furthermore, the keeping qualities of food preserved by such methods are limited as to time. Where a product is to be preserved in definitely or for a long period of time, some other means of preservation ordinarily must be utilized.
The invention of the microscope and the subsequent dis covery of microorganisms аs a major cause of food spoilage led to the development of canning in France during the time of Napoleon. With the invention of canning, man found a way to preserve food of all kinds in large quantities and for indefinite periods of time. Canned foods have the advantage of being almost entirely imperishable, easily processed, and convenient to handle and store. Today, more food is preserved by canning than by all other methods combined. The one big disadvantage of canning is that canned foods must be heat-sterilized, which frequently results in over cooking. Hence, although canned foods often have a distinctive and delicious flavor of their own, they usually differ greatly from the original fresh product.
The only means of preserving food in its original fresh state is by refrigeration. This, of course, is the principal advantage that refrigeration has over other methods of food preservation. However, refrigeration too has its disadvantages, for instance, when food is to be preserved by refrigeration, the refrigerating process must begin very soon after harvesting or killing and must be continuous until the food is finally consumed. Since this requires relatively expensive and bulky equipment, it is often both inconvenient and uneconomical.
Obviously, then, there is no one method of food preser vation which is best in all cases and the particular method used in any one case will depend upon a number of factors, such as the type of product, the length of time the product is to be preserved, the purpose for which the product is to be used, and the availability of transportation and storage equipment. Very often it is necessary to employ several methods simultaneously in order to obtain the desired results.
Deterioration and Spoilage
Since the preservation of food is simply a matter of pre venting or retarding deterioration and spoilage regardless of the method used, a good knowledge of the causes of deterioration and spoilage is a prerequisite to the study of preservation methods.
It should be recognized at the outset that there are degrees of quality and that all perishable foods pass through various stages of deterioration before becoming unfit for consumption. In most cases, the objective in the preserva tion of food is not only to preserve the foodstuff in an edible condition but also to preserve it as nearly as possible at the peak of its quality with respect to appearance, odor, taste, and vitamin content. Except for a few processed foods, this usually means maintaining the foodstuff as nearly as possible in its original fresh state.
Any deterioration sufficient to cause a detectable change in the appearance, odor, or taste of fresh foods immediately reduces the commercial value of the product and thereby represents an economic loss.
For obvious reasons, maintaining the vitamin content at the highest possible level is always an important factor in the processing and/or preservation of all food products. In fact, many food processors, such as bakers and dairy workers, are now adding vitamins to their product to replace those which are lost during processing. Fresh vegetables, fruit, and fruit juices are some of the food products which suffer heavy losses in vitamin content very quickly if they are not handled and protected properly. Although the loss of vitamin content is not something which in itself is apparent, in many fresh foods it is usually accompanied by recognizable changes in appearance, odor, or taste, such as, for instance, wilting in leafy, green vegetables.
For the most part, the deterioration and eventual spoilage of perishable food are caused by a series of complex chemical changes which take place in the foodstuff after harvesting or killing. These chemical changes are brought about by both internal and external agents. The former are the natural enzymes which are inherent in all organic materials, whereas the latter are microorganisms which grow in and on the surface of the foodstuff.
Control of Spoilage Agents
All methods of food preservation must involve manipulation of the environment in and around the preserved product in order to produce one or more conditions unfavorable to the continued activity of the spoilage agents. When the product is to be preserved for any length of time, the unfavorable conditions produced must be of sufficient severity to eliminate the spoilage agents entirely or at least render them ineffective.
All types of spoilage agents are destroyed when subjected to high temperature over a period of time. This principle is used in preservation of food by canning. The temperature of the product is raised to a level fatal to all spoilage agents and is maintained at this level until they are all destroyed. The product is then sealed in sterilized air-tight containers to prevent recontami-nation. A product so processed will remain in a preserved state indefinitely.
The exposure time required for the destruction of all spoilage agents depends upon the temperature level. The higher the temperature level, the shorter is the exposure period required. In this regard, moist heat is more effective than dry heat because of its greater penetrating power. When moist heat is used, the temperature level required is lower and the processing period is shorter. Enzymes and all living microorganisms are destroyed when exposed to the temperature of boiling water for approximately five minutes, but the more resistant bacteria spores may survive at this condition for several hours before succumbing. For this reason, some food products, particularly meats and nonacid vegetables, require long processing periods which frequently result in overcooking of the product. These products are usually processed under pressure so that the processing temperature is increased and the processing time shortened.
Another method of curtailing the activity of spoilage agents is to deprive them of the moisture and/or food which are necessary for their continued activity. Both enzymes and microorganisms require moisture to carry on their activities. Hence, removal of the free moisture from a product will severely limit their activities. The process of moisture removal is called drying (dehydration) and is one of the oldest methods of preserving foods. Drying is accomplished either naturally in the sun and air or artificially in ovens. Dried products which are stored in a cool, dry place will remain in good condition for long periods.
Pickling is essentially a fermentation process, the end result of which is the exhaustion of the substances which serve as food for yeasts and bacteria. The product to be preserved by pickling is immersed in a salt brine solution and fermentation is allowed to take place, during which the sugars contained in the food product are converted to lactic acid, primarily through the action of lactic acid bacteria.
Smoked products are preserved partially by the drying effect of the smoke and partially by antiseptics which are absorbed from the smoke.
Too, some products are "cured" with sugar or salt which act as preservatives in that they create conditions unfavorable to the activity of spoilage agents. Some other frequently used preservatives are vinegar, borax, saltpeter, benzoate of soda, and various spices. A few of the products preserved in this manner are sugar-cured hams, salt pork, spiced fruits, certain beverages, jellies, jams, and preserves.
Preservation by Refrigeration
The preservation of perishables by refrigeration involves the use of low temperature as a means of eliminating or retarding the activity of spoilage agents. Although low temperatures are not as effective in bringing about the destruction of spoilage agents as are high temperatures, the storage of perishables at low temperatures greatly reduces the activity of both enzymes and microorganisms and thereby provides a practical means of preserving perish ables in their original fresh state for varying periods of time. The degree of low temperature required for adequate preservation varies with the type of product stored and with the length of time the product is to be kept in storage.
For purposes of preservation, food products can be grouped into two general categories: (1) those that are alive at the time of distribution and storage and (2) those that are not. Nonliving food substances, such as meat, poultry, and fish, are much more susceptible to microbial contamination and spoilage than are living food substances, and they usually require more stringent preservation methods.
With nonliving food substances, the problem of preserva tion is one of protecting dead tissue from all the forces of putrefaction and decay, both enzymic and microbial. In the case of living food substances, such as fruit and vege tables, the fact of life itself affords considerable protec tion against microbial invasion, and the preservation prob lem is chiefly one of keeping the food substance alive while at the same time retarding natural enzymic activity in order to slow the rate of maturation or ripening.
Freezing and Frozen Storage
When a product is to be preserved in its original fresh state for relatively long periods, it is usually frozen and stored at approximately 0oF or below. The list of food products commonly frozen includes not only those which are preserved in their fresh state, such as vegetables, fruit.
The following factors govern the ultimate quality and sto rage life of any frozen product:
1. The nature and composition of the product to be frozen.
2. The care used in selecting, handling, and preparing the pro duct for freezing.
3. The freezing method.
4. The storage conditions.
Only high quality products in good condition should be frozen. With vegetables and fruit, selecting the proper variety for freezing is very important. Some varieties are not suitable for freezing and will result in a low quality product or in one with limited keeping qualities.
Vegetables and fruit to be frozen should be harvested at the peak of maturity and should be processed and frozen as quick ly as possible after harvesting to avoid undesirable chemical changes through enzymic and microbial action.
Both vegetables and fruit require considerable processing before freezing. After cleaning and washing to remove foreign materials – leaves, dirt, insects, juices, etc. – from their sur faces, vegetables are "blanched" in hot water or steam at 212°F in order to destroy the natural enzymes. It should be remembered that enzymes are not destroyed by low temperature and, although greatly reduced, their activity continues at a slow rate even in food stored at 0oF and below. Hence, blanching, which destroys most of the enzymes, greatly increases the storage of frozen vegetables. The time required for blanching varies with the type and variety of the vegetable and ranges from 1 to 1.5 min. for green beans to 11 min. for large ears of corn. Although much of the microbial population is destroyed along with the enzymes during the blanching process, many bacteria survive. To prevent spoilage by these viable bacteria, vegetables should be chilled to 50°F immediately after blanching and before they are packaged for the freezer.
One can certainly agree that the science and technique of refrigeration are now old and extensive enough for people to wish to find out dates and circumstances of some discovery, to get information on how actual refrigeration techniques had been initiated. If one tried to sketch a history of “artificial” refrigeration, i.e. which is man-made, its presentation could be divided into four epochs:
– from 1755 to 1875;
– from 1875 to 1914;
– between the two wars;
– after 1945.
The year of 1755 can be considered to be the starting point of the history of "artificial" refrigeration. It goes without saying that man did not wait for this date to exercise his abilities and thoughts in the use of natural refrigeration. In this "pre-historic" period one may distinguish: the period, during which man was content to gather the natural god-given refrigeration; then another one, during which man "grew" this natural source of cold, and improved the uses which he made of it.
Starting at 1755, the history of refrigeration began: man then knew how to produce the low temperatures from which he has benefited during the ages. During the 120 years which passed, from 1755 to 1875, the first refrigerating apparatuses and machines were made and devel oped by several precursors whose inventive engineering is admir able. Parallel to this, the branches of physics were developed and organized, on which the many processes of production of refrigeration, and later the improvement of refrigerating machines, rest. It is mainly after 1875 that refrigeration techniques began to benefit from thermodynamics. During this period 1755 to 1875, the two scientific and technical streams, on which the future and development of refrigeration were based, practically did not mix.
When the second epoch (1875-1914) opened, it was known how to produce cold by all the systems which are in use today, with the exception of a few proce dures which are only employed in very special circumstances such as the Ranque effect, or the magnetic procedures for obtaining very low tem peratures.
At the beginning of the period, there were three types of use of re frigeration which attracted the most interest, namely ice making (for vari ous uses), transport of meat by sea, and brewing. Cold stores were set up to receive the overseas meat, as well as provision stores in large towns. The rough outline of "cold chains" took shape, the chief links being the cold stores and the refrige rated ships which carried the meat. Refrigerated rail transport was very slow to start, except in the United States where the development was rapid, and to a lesser extent, in Russia.
The need for cooling grew very rapidly in the foodstuffs field. Besides the three categories which have just been mentioned and which were the first motive forces behind development, applications of refrigeration in creased for fruits, milk, eggs and fish and in diverse foodstuffs industries. Nearly all the techniques used in these fields, and which we know today, were introduced during this period. They have, of course, been consider ably improved and refined since, and have also been associated with technological innovations and developments of all sorts, not specifically of refrigeration, e.g. in materials for transport, building, and handling. These developments often make the processes appear to be quite different from those in use at the turn of the century. But the roots of the techniques nearly always are to be found in this epoch.
Further, one may consider that 1900 was to some extent a turning point in this epoch, in the sense that prior to that date the main interest was in development of refrigeration plant, and it was not until about 1900 that real interest began to be taken in the behavior of foodstuffs and to determining the optimum conditions in which to hold them.
Outside the foodstuffs field, this period also saw very diverse appli cations of refrigeration but using only a minute fraction of the total in stalled refrigeration capacity. Many industries already used refrigeration. Liquefaction of air on an industrial scale began at the turn of the cen tury, and during this period success followed attempts to liquefy several "permanent gases", which had not been possible in the preceding pe riod. Processes such as freeze-drying (1906), or physical phenomena such as superconductivity (1911) were discovered, which only found applica tion in later times.
The production of refrigeration became increasingly industrialized to cope with the growing diverse requirements. At the same time, the situ ation became clearer, as the system of compression of liquefiable gases became more and more dominant.
The war of 1914 to 1918 was not an interlude between two epochs in the history of refrigeration. On the contrary, the nations engaged in the conflict in 1914 were immediately faced with the increased need of meat to supply the troops, and consequently had to provide refrigerating equipment to store and transport this foodstuff. Thus France, at the very beginning of the war,
had to make use of frozen meat imported by Great Britain, and to expand its fleet of refrigerated wagons. During the same period, France's cold stores increased four times. A similar rate of increase took place in Italy. In Great Britain the effect was smaller, because this country was well equipped before the war; however, between 1913 and 1923, the volume of cold stores increased more than 1,5 times. In the United States, the installed refrigerating capacity was
practically doubled, from 1911 to 1923. Russia built seven small military cold stores in wood, cooled by ice and salt with powerful fans, to freeze meat, and also imported about fifty American refrigerating compressors. This was little enough in relation to requirements, but the number of refriger ated wagons doubled from 3000 in 1914 to 6000 in 1920.
During the two decades between the two wars, refrigeration conquered a geographical territory which was very extensive, since many countries began to be interested in and installed refrigeration facilities. To follow the growth of equipment and refrigeration applications in the whole world is thus more difficult than in the preceding period when a few countries only were really involved. The United States held its preeminence in the field of refrigeration, and after the First World War it became the most powerful industrial nation in the world. The economic power of Germany remained very important. The British economy showed signs of weakness at the beginning of the 1920s, even before the American crisis of the 1930s, begun by the Wall Street crash in 1929, and these factors slowed down the rate of ex pansion in the western world. In the world of refrigeration, the period between the two wars has not seen the same spate of ideas and enterprises as in the last decades of the 19th century.
When the history of refrigeration after the Second World War is considered, one is immediately struck by the extraordinary increase in the ways in which cold is used, all over the world, and by the extreme diversity of these applications. Many more things took place in the field of refrigeration from 1945 to 1975 than between the two wars. It must at once be stated that applications to the field of foodstuffs, while remaining very impor tant worldwide, are not as outstanding as in the past.
To cope with this considerable expansion, the production of cold has expanded in parallel, without, however, there being any important chan ges in the means of production during this period, apart from the screw compressor. But the changes and improvements brought into use just before the second war have become standard industrial practice, notably in piston compressors, turbo compressors and absorption machines.
Firstly, we have seen in this epoch the strengthening of the equipment in those countries which were already well established users of refrigeration, as well as the introduction of equipment into countries newly coming into the world of refrigeration. This remark is somewhat trite by itself, and something analogous was already happening between the wars, but now the phenomenon has gained impetus. In fact, from 1950 and for about a quarter of a century, the industrialized nations have known a remarkable economic growth; the speed of growth was, for a time, even faster in Europe and in Japan than it was in the United Sta tes. Those countries were thus catching up to the U.S.A. This pro cess of catching up has been seen not only to the United States, but also to other countries which were the leaders in the beginnings of refriger ation. We must deplore that the poor non-industrialized countries, most of which have climates which would render the use of refrigeration very beneficial, have stood aside from this "blossoming" of refrigeration.
If one desired to give an appreciation of the means of producing cold during this period after the wars, it would seem that on a world scale it would have to be said that there was little in the way of sensational novelties, but rather extrapolation and extension of the techniques available in 1939. Much in technological refinements, but less of novelties than in preceding epochs. This appreciation would have to be completed by the following observation: equipment used almost uniquely in one country in 1939 expanded rapidly elsewhere after the war.
The period knew several false starts, trials which had not achieved the expected success, e.g. the small magnetic compressor and thermo-electric refrigeration. On the other hand, the air cycle machine, completely forgotten between the wars, surfaced again in some countries.
A further remark: the unit sizes of large refrigerating machines (of all sorts) continued to grow, mainly to satisfy the requirements of air conditioning, and some industries. The compression refrigerating system continued to lead the field.
A
addition – подвод
~ of heat – подвод тепла
agent – агент, средство
refrigerating ~ – холодильный агент, хладагент
aggregation – масса
ammonia – аммиак
amount – количество, сумма, величина
attraction – притяжение
В
baffling – перегородка
bake – печь, выпекать
blanch – бланшировать
brine – рассол, раствор
salt ~ – соляной раствор
С
can – консервная банка, консервировать в банках
canning – баночное консервирование, производство банок консервов,
консервный,
capacity – способность, мощность, производительность
refrigerating ~ – холодопроизводительность
charge – загружать, заряжать
electrical ~ – электрический заряд
chloride – хлорид
ammonium ~ — хлористый аммоний, нашатырный спирт
calcium ~ – хлористый кальций
sodium ~ – хлористый натрий
methyl ~ – хлористый метил, Фреон–40
methylene ~ – дихлорметан, Фреон–50
chlorine – хлор
coefficient – коэффициент
~ of expansion – коэффициент расширения
cohesion – межмолекулярная связь
compartment– отделение, отсек, камера
ice ~ – отделение для льда
conditioning – кондиционирование
air ~ – кондиционирование воздуха
conduction – проводимость
conductivity – проводимость, удельная проводимость
contaminate – загрязнять; портить, оказывать пагубное действие
contamination – загрязнение
microbial ~ – загрязнение микробами
content – содержание
vitamin ~ – содержание витаминов,
convection – конвекция.
cool – охлаждать, холодный, прохладный
cooling – охлаждение
latent ~ – охлаждение посредством испарения или таяния хладагента.
sensible ~ – охлаждение посредством отвода ощутимого тепла хладагента
cost – стоимость, цена
initial ~ – первоначальная стоимость
cure – консервировать; сушить, вялить,
cycle – цикл
vapor-compression ~ – парокомпрессионный цикл
D
dairy – молочный завод, молочный,
decay – гниение, распад
degree – степень, градус
deterioration – ухудшение, порча.
dioxide – двуокись
carbon ~ – двуокись углерода, углекислота; углекислый газ
sulfur ~ – двуокись серы, сернистый ангидрид
dry – сушить (ся)
drying – сушка
Е
effect – эффект, действие; производительность
refrigerating ~ – холодопроизводительноеть
enzyme – энзим, фермент
F
flammability – воспламеняемость
flammable – огнеопасный, легковоспламеняющийся
flavor – вкус; аромат, запах; привкус
fluid – газо-жидкостная среда, текучий, движущийся,
working ~ – рабочее вещество (в холодильной машине)
food – пища, питание, продовольствие, пищевые продукты
foodstuffs – продовольствие, продукт питания
G
gain – получать, добывать, увеличение, прирост
heat ~ – приток тепла
Н
handle – грузить, транспортировать
harvest – урожай, собирать урожай
harvesting – сбор урожая
heat – теплота, тепло
latent ~ – скрытая теплота
sensible ~ – ощутимая теплота
specific ~ – удельная теплота, удельная теплоемкость
hydrocarbon – углеводород
fluorinated ~ – фторированный углеводород
I
ice – лед
cracked ~ – дробленый лед
index – показатель
insulate – изолировать
insulation – изолирование, изоляция
К
kill – убивать, забивать, резать (скот)
killing – убой (скота)
L
life – жизнь, срок
storage ~ – срок хранения
load – нагрузка
cooling ~ – тепловая нагрузка холодильного оборудования
heat ~ – тепловая нагрузка холодильного оборудования
refrigeration ~ расход холода, тепловая нагрузка холодильного оборудо-
вания
total ~ – общая нагрузка, суммарная нагрузка
M
maintenance – уход, содержание в исправности, текущий ремонт,
эксплуатация, эксплуатационные расходы
material – вещество, материал
raw ~ – сырье
matter – вещество, материя
maturation – созревание
maturity – зрелость, спелость
medium ( мн. число: media) – среда
О
odor – запах, аромат
overcooking – перевар, чрезмерно длительная варка
Р
pan – поддон
drip ~ – поддон для талой воды
perishable – скоропортящийся продукт, скоропортящийся
pickle – консервировать засолом, квашением, маринованием
pickling – засол, квашение, маринование
plant – установка , агрегат
ice ~ – установка для производства льда, льдозавод, льдогенератор
point – точка
boiling ~ – точка кипения
freezing ~ – точка замерзания
reference ~ – точка отсчета
zего point – нулевая точка; точка отсчета
population – популяция, обсемененность
preservation – сохранение, предохранение, консервирование
рpreservative – предохраняющее средство, консервант
preserve – сохранять, предохранять; консервировать
preserves – презервы, полуконсервы
process – подвергать технологической обработке
processing – технологическая обработка продукта
property – характеристика, свойство, качество
putrefaction — гниение, разложение
Q
quality – качество, сорт, класс
keeping ~ – стойкость при хранения, сохраняемость
R
radiation – излучение
range – диапазон, интервал
temperature ~ – диапазон температур, температурный интер вал
rate – тeмп, скорость, норма, интенсивность
~ of refrigeration – скорость (интенсивность) охлаждения
refrigerating ~ – скорость охлаждения
read – показывать (о приборе)
reading – показания прибора
refrigerant – охладитель, хладагент
fluorocarbon ~ – фторированный углеводородами хладагент
refrigeration – охлаждение (искусственное)
refrigerate – охлаждать (ся)
refrigerator – холодильный машина, (шкаф, камера)
commercial ~ – торговый холодильник (шкаф, малая холодильная камера)
domestic ~ – домашний холодильник
ice ~ – холодильный шкаф c ледяным охлаждением
removal – отвод
~ of heat – отвод тепла
ripening – созревание
S
salt – соль, засаливать
salting – посол, засол
saltpeter – селитра
scale – шкала
Celsius ~ – шкала Цельсия
centigrade ~ – стоградусная шкала, шкала Цельсия
Fahrenheit ~ – шкала Фаренгейта
temperature ~ – температурная шкала
smoke – дым, копоть || коптиться
smoking – копчение
sodium – натрий
space – пространство
refrigerated ~ – охлаждаемое пространство
storage ~ – пространство холодильника для хранения при низкой
температуре
spice – специя, пряность
spoilage – порча
state – состояние
(heat)-sterilize – стерилизовать (теплом)
storage – хранение
store – запас, склад, накапливать, запасать
surroundings – окружающая среда
system – система , установка
mechanical refrigerating ~ – холодильная установка c меха ническим ох-
лаждением
T
taste – вкус, иметь вкус, пробовать на вкус, дегустировать
temperature – температура
freezing ~ – температура замерзания
saturation ~ – температура насыщения
storage ~ – температура хранения
tissue – ткань
toxic – токсичный
toxicity – токсичность
U
unit – единица (измерения), единица, установка, прибор
British thermal ~ – Британская тепловая единица
V
value – ценность, стоимость, цена
commerсial ~ – продажная цена
vinegar – уксус
СОДЕРЖАНИЕ
|
[1] [2] Введение
[3] [4] MATTER, INTERNAL ENERGY, HEAT, TEMPERATURE
[5] [6] REFRIGERATION AND REFRIGERANTS
[7] [8] REFRIGERATION APPLICATIONS [9] ПРИЛОЖЕНИЕ
[10] A HISTORY OF ARTIFICIAL REFRIGERATION [11] СЛОВАРЬ ТЕРМИНОВ |
Васильева Лилия Александровна
Домбровская Антонина Васильевна
АНГЛИЙСКИЙ ЯЗЫК
Методические указания
по подготовке к контрольным работам 5 и 6
для студентов 2-го курса всех специальностей
заочной формы обучения
Редактор
Л.Г. Лебедева
Корректор
Н.И. Михайлова
Компьютерная верстка
Н.В. Гуральник
_____________________________________________________________________
Подписано в печать 26.08.2010. Формат 6084 1/16
Усл. печ. л. 2,56. Печ. л. 2,75. Уч.-изд. л. 2,44
Тираж 300 экз. Заказ № C 36
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