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Principles Of Refrigeration And Air Conditioning Pdf

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Air conditioning can be used in both domestic and commercial environments. This process is most commonly used to achieve a more comfortable interior environment, typically for humans and other animals; however, air conditioning is also used to cool and dehumidify rooms filled with heat-producing electronic devices, such as computer servers , power amplifiers , and to display and store some delicate products, such as artwork. The cooling is typically achieved through a refrigeration cycle , but sometimes a passive cooling system such as evaporation or free cooling is used.

The work of energy transfer is traditionally driven by mechanical means, but can also be driven by heat, magnetism , electricity , laser , or other means. Refrigeration has many applications, including household refrigerators , industrial freezers , cryogenics , and air conditioning. Heat pumps may use the heat output of the refrigeration process, and also may be designed to be reversible, but are otherwise similar to air conditioning units.

Refrigeration

A chiller is simply a device that is used to remove heat from something. For industrial purposes, chillers can be thought of as a component within a complex mechanical system that is used to remove heat from a process or substance.

To really understand what a chiller is, a fundamental knowledge of the principles of basic refrigeration is required. A chiller is simply a device that used to remove heat from something. Welcome to Berg's School of Cool. Before getting into the fundamentals of refrigeration, a few basic definitions should be considered:. Heat is a form of energy transferred by virtue of a difference in temperature. Heat exists everywhere to a greater or lesser degree. As a form of energy it can be neither created or destroyed, although other forms of energy may be converted into heat, and vice versa.

It is important to remember that heat energy travels in only one direction; from a warmer to a cooler object, substance, or area. Cold is a relative term referring to the lack of heat in an object, substance, or area. Another definition describes it as the absence of heat, no process yet has been devised of achieving "absolute zero," the state in which all heat has been removed from any object, substance, or area. Theoretically this zero point would be Refrigeration , or cooling process, is the removal of unwanted heat from a selected object, substance, or space and its transfer to another object, substance, or space.

Removal of heat lowers the temperature and may be accomplished by use of ice, snow, chilled water or mechanical refrigeration. Mechanical refrigeration , is the utilization of mechanical components arranged in a " refrigeration system " for the purpose of transferring heat.

Refrigerants , are chemical compounds that are alternately compressed and condensed into a liquid and then permitted to expand into a vapor or gas as they are pumped through the mechanical refrigeration system to cycle.

The refrigeration cycle is based on the long known physical principle that a liquid expanding into a gas extracts heat from the surrounding substance or area. You can test this principle by simply wetting your finger and holding it up. It immediately begins to feel cooler than the others, particularly if exposed to some air movement. That's because the liquid in which you dipped it is evaporating, and as it does, it extracts heat from the skin of the finger and air around it.

Refrigerants evaporate or "boil" at much lower temperatures than water, which permits them to extract heat at a more rapid rate than the water on your finger. The job of the refrigeration cycle is to remove unwanted heat from one place and discharge it into another. To accomplish this, the refrigerant is pumped through a closed refrigeration system.

If the system was not closed, it would be using up the refrigerant by dissipating it into the surrounding media; because it is closed, the same refrigerant is used over and over again, as it passes through the cycle removing some heat and discharging it.

The closed cycle serves other purposes as well; it keeps the refrigerant from becoming contaminated and controls its flow, for it is a liquid in some parts of the cycle and a gas or vapor in other phases.

Let's look at what happens in a simple refrigeration cycle, and to the major components involved. The metering device is a point where we will start the trip through the cycle. This may be a thermal expansion valve, a capillary tube, or any other device to control the flow of refrigerant into the evaporator, or cooling coil, as a low-pressure, low-temperature refrigerant. The expanding refrigerant evaporates changes state as it goes through the evaporator, where it removes the heat from the substance or space in which the evaporator is located.

Heat will travel from the warmer substance to the evaporator cooled by the evaporation of the refrigerant within the system, causing the refrigerant to "boil" and evaporate, changing it to a vapor. This is similar to the change that occurs when a pail of water is boiled on the stove and the water changes to steam, except that the refrigerant boils at a much lower temperature.

Now this low-pressure, low-temperature vapor is drawn to the compressor where it is compressed into a high-temperature, high-pressure vapor. The compressor discharges it to the condenser, so that it can give up the heat that it picked up in the evaporator. The refrigerant vapor is at a higher temperature than the air passing across the condenser air-cooled type ; or water passing through the condenser water-cooled type ; therefore that is transferred from the warmer refrigerant vapor to the cooler air or water.

In this process, as heat is removed from the vapor, a change of state takes place and the vapor is condensed back into a liquid, at a high-pressure and high-temperature. The liquid refrigerant travels now to the metering device where it passes through a small opening or orifice where a drop in pressure and temperature occurs, and then it enters into the evaporator or cooling coil. As the refrigerant makes its way into the large opening of the evaporator tubing or coil, it vaporizes, ready to start another cycle through the system.

The refrigeration system requires some means of connecting the basic major components - evaporator, compressor, condenser, and metering device - just as roads connect communities. Tubing or "lines" make the system complete so that the refrigerant will not leak out into the atmosphere. The suction line connects the evaporator or cooling coil to the compressor, the hot gas or discharge line connects the compressor to the condenser, and the liquid line is the connecting tubing between the condenser and the metering device Thermal expansion valve.

Some systems will have a receiver immediately after the condenser and before the metering device, where the refrigerant is stored until it is needed for heat removal in the evaporator. There are many different kinds and variations of the refrigeration cycle components. For example, there are at least a half dozen different types of compressor, from the reciprocating, piston through a screw, scroll and centrifugal impeller design, but the function is the same in all cases - that of compressing the heat laden vapor into a high-temperature vapor.

The same can be said of the condenser and evaporator surfaces. They can be bare pipes, or they can be finned condensers and evaporators with electrically driven fans to pass the air through tem, or with a condenser pump to pump the water through a water-cooled condenser. There are a number of different types of metering devices to regulate the liquid refrigerant into the evaporator, depending on size of equipment, refrigerant used, and its application.

The mechanical refrigeration system described above is essentially the same whether the system be a domestic refrigerator, a low-temperature freezer, comfort air conditioning system, industrial chiller, or commercial cooling equipment. Refrigerants will be different and size of the equipment will vary greatly, but the principle of operation and the refrigeration cycle remains the same.

Thus, once you understand the simple actions that are taking place within the refrigeration mechanical cycle you should have a good understanding how a refrigeration system works.

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All known matter exists in one of three physical forms or states: solid, liquid, or gaseous. There are distinct dissimilarities among these physical states namely:. Matter in a liquid state will retain its quantity and size but not its shape. The liquid will always conform to the occupying container. If a cubic foot of water in a container measuring 1 foot on each side is transferred to a container of different rectangular dimensions, the quantity and volume of the water will be the same although the dimension will change.

Matter in solid state will retain its quantity, shape, and physical dimensions. A cubic foot of wood will retain its weight, size, and shape even if moved from place to place. Matter in gaseous state does not have a tendency to retain either its size or its shape. If a one foot cylinder containing steam or some other gas is connected to a 2-cubic foot cylinder on which a vacuum has been drawn, the vapor will expand to occupy the volume of the large cylinder.

Although these specific differences exist in the three states of matter, quite frequently, under changing conditions of pressure and temperature, the same substance may exist in any one of the three states, such as a solid, a liquid, or vapor ice, water, and steam, for example. Solids always have some definitive shape, whereas liquids and gases have no definitive shape of their own, but will conform to the shape of their containers.

All matter is composed of small particles known as molecules, for the present we will concern ourselves only with the molecule, the smallest particle into which any matter or substance can be broken down and still retain its identity.

Molecules vary in shape, size, and weight. In physics we learn that molecules have a tendency to cling together. When heat energy is applied to a substance it increases the internal energy of the molecules, which increase their motion or velocity of movement.

With this increase in the movement of the molecules, there is also rise or increase in the temperature of the substance. When heat is removed from a substance, it follows that the velocity of the molecular movement will decrease and also that there will be a decrease or lowering of the internal temperature of the substance. When a solid substance is heated, the molecular motion is chiefly in the form of rapid motion back and forth, the molecules never moving far from their normal or original position.

But at some given temperature for that particular substance, further addition of heat will not necessarily increase the molecular motion within the substance; instead, the additional heat will cause some solids to liquefy change into a liquid. Thus the additional heat causes a change of state in the material.

The temperature at which this change of state in a substance takes place is called its melting point. Let us assume that a container of water at 70 deg F, in which a thermometer has been placed, is left in the freezer for hours.

When it is taken from the freezer, it has become a block of ice - solidification has taken place. Let us further assume that the thermometer in the ice block indicates a temperature of 20 deg F.

If it is allowed to stand at room temperature, heat from the room air will be absorbed by the ice until the thermometer indicates a temperature of 32 deg F, when some of the ice will begin to change into water. With heat continuing to transfer from the room air to the ice, more ice will change back into the water; but the thermometer will continue to indicate a temperature a temperature of 32 deg F until all the ice has melted.

Liquefaction has now taken place. Thus far we have learned how solids can change into liquid, and how a liquid can change in to a vapor but it is possible for a substance to undergo a physical change through which solid will change directly into a gaseous state without first melting into a liquid.

This is known as a sublimation. As an example, dry ice CO2 at atmospheric conditions sublimes directly into vapor. Most of us are acquainted with common measurement, such as those pertaining to length, weight, volume, etc. Heat is a form of energy which is not measurable in itself; but the heat intensity, or temperature of a substance, can be measured. In the discussion of state of matter, temperature was discussed, as was the addition or removal of heat.

Relatively, water is colder than steam; yet it is, at the same time, warmer than ice. Temperature scales were formulated through use of glass tubes with similar interior diameter and reservoir for the liquid - such as mercury - that will expand and rise up in the tube when heated. The Fahrenheit thermometer or scale is based on the relative position of the mercury in the thermometer when water is at the freezing point and when water is boiling.

The point where water either will freeze, or ice will melt, under normal atmospheric conditions, was labeled as 32 degrees; whereas the location, or point on the thermometer where water will boil was labeled degrees; whereas the thermometer has been the one most commonly used in most types of refrigeration engineering work.

A Celsius thermometer formerly called a Centigrade thermometer , is used in chemistry and physics, especially in continental Europe, south Americas and Asia. A frequently asked question is why the boiling point of water and the melting point of ice where used as the standard for both thermometers. These points or temperatures were chosen because water has a very constant boiling and freezing temperature, and water is a very common substance.

Most frequently a conversion from one temperature scale to other is made by the use of a conversion table, but if one is not available, the conversion can be done easily by a formula using these equations:. Thus far, in measurement of heat intensity, we have located two definitive reference points - the freezing point and the boiling point of water on both the Fahrenheit and Celsius scales.

We now must locate still a third definite point - absolute zero. This is the point where, it is believed all molecular action ceases. As already noted on the Fahrenheit temperature scale, this is about Deg. F, while on the Celsius scale it is about Deg. Certain basic laws, are based on the use of absolute temperatures.

Refrigeration and Air Conditioning - Third Edition

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Air-Conditioning and Refrigeration. Oil management; gas and liquid separation; subcooling, superheating, desuperheating, and piping of refrigerant liquid, gas, and two-phase flow are all part of refrigeration. Wang Publisher. Chapter 3. Chapter Start by pressing the button below! If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site.

Thermodynamics and Design Principles of Refrigeration Systems

This book has been written especially for use in programs where a full curriculum in refrigeration is offered. However, the material covered and the method of presentation are such that the text is also suitable for adult evening classes and for on-the-job training and self-instruction. Furthermore, the material is so arranged and sectionalized that this textbook is readily adaptable to any level of study and to any desired method or sequence of presentation. Despite a rigorous treatment of the thermodynamics of the cycle, application of the calculus is not required nor is an extensive background in physics and thermodynamics presupposed. The first four chapters deal with the fundamental principles of physics and thermodynamics upon which the refrigeration cycle is based.

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Air conditioning

Compressors , Psychrometry and Applications of Refrigeration and Air Conditioning have been included and updated for students to conceptualise the subject in a complete manner. The chapters consist of various exercises, examples, and multiple illustrations that aid in understanding the subject better. The subject of refrigeration and airconditioning is one of great significance as public focus shifts to food processing and preservation technologies. This highlights the need for professionals well-versed in the basics of this technology.

A chiller is simply a device that is used to remove heat from something. For industrial purposes, chillers can be thought of as a component within a complex mechanical system that is used to remove heat from a process or substance. To really understand what a chiller is, a fundamental knowledge of the principles of basic refrigeration is required. A chiller is simply a device that used to remove heat from something.


to , Wang Published Principles of Refrigeration Engineering and Air Conditioning as the teaching and learning package, and presented several papers at.


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 А как же автоматическое отключение. Стратмор задумался. - Должно быть, где-то замыкание. Желтый сигнал тревоги вспыхнул над шифровалкой, и свет, пульсируя, прерывистыми пятнами упал налицо коммандера. - Может, отключить его самим? - предложила Сьюзан.

Пальцы у него онемели. Он упал. И в следующее мгновение не осталось ничего, кроме черной бездны. ГЛАВА 102 Стратмор спустился на нижний этаж ТРАНСТЕКСТА и ступил с лесов в дюймовый слой воды на полу. Гигантский компьютер содрогался мелкой дрожью, из густого клубящегося тумана падали капли воды. Сигналы тревоги гремели подобно грому. Коммандер посмотрел на вышедший из строя главный генератор, на котором лежал Фил Чатрукьян.

Фонтейн набрал код на специальной углубленной панели, после чего прикоснулся к небольшой стеклянной пластинке. Сигнальная лампочка вспыхнула, и массивная стена с грохотом отъехала влево. В АНБ было только одно помещение, еще более засекреченное, чем шифровалка, и Сьюзан поняла, что сейчас она окажется в святая святых агентства. ГЛАВА 109 Командный центр главного банка данных АНБ более всего напоминал Центр управления полетами НАСА в миниатюре. Десяток компьютерных терминалов располагались напротив видеоэкрана, занимавшего всю дальнюю стену площадью девять на двенадцать метров. На экране стремительно сменяли друг друга цифры и диаграммы, как будто кто-то скользил рукой по клавишам управления. Несколько операторов очумело перебегали от одного терминала к другому, волоча за собой распечатки и отдавая какие-то распоряжения.

Однако одиночество не принесло ей успокоения. В голове у Сьюзан беспрестанно крутилась мысль о контактах Танкадо с Хейлом. Кто будет охранять охранников.

Сьюзан на мгновение заколебалась и оглянулась на заблокированную дверь. Всего двадцать минут, подумала. Повернувшись к терминалу Хейла, Сьюзан вдруг уловила странный мускусный запах - очень необычный для Третьего узла. Она подумала, что дело, быть может, в неисправном ионизаторе воздуха.

Сказал, что ТРАНСТЕКСТ работает в обычном темпе. Что у нас неверные данные.

4 Comments

Elias G. 28.05.2021 at 10:02

The knowledge of refrigeration systems would help HVAC engineers in selection of the equipment and Basic principles of refrigerator and heat pump. (Source.

Nate C. 29.05.2021 at 05:18

2- Source unite which represent the chiller in cooling system or the boiler and furnace in heating systems. 3-Distribution systems which represents the piping and.

Fiorel T. 30.05.2021 at 22:38

Subjects with exceptional longevity and their offspring have significantly greater high-density lipoprotein, a replica of the actual painting.

Eliot C. 06.06.2021 at 23:42

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