Refrigeration working principle pdf

Refrigerators and air conditioners both work on the principle of cooling through evaporation. A refrigerator consists of two storage compartments — one for frozen items and the other for items requiring refrigeration but not freezing. By understanding how the basic refrigeration cycle work; we also know how air conditioning works. The basic principles behind the refrigeration cycle and air conditioning are the same.

Working substance in air conditioning is the moist air which is a mixture of two gases. One of these is dry air which itself is a mixture of a number of gases and the The Air Conditioning and Refrigeration Center was founded in with a grant from the estate of Richard W. Refrigeration and Air Conditioning By C P Arora Pdf A major application area of thermodynamics is refrigeration, which is the transfer of heat from a lower temperature region to a higher temperature one.

Refrigeration and Air Conditioning Objectives of the lesson: 1. Define refrigeration and air conditioning 2. Introduce aspects of various natural refrigeration methods, namely: Use of ice transported from colder regions Use of ice harvested in winter and stored in ice houses Use of evaporative cooling 3. Introduce historical aspects of various artificial refrigeration methods, … refrigeration working principle pdf 4 Heat, work, energy and power. When working with refrigeration systems the.

Refrigeration effect Q c Input. The basic principle of refrigeration is simple. Download eBooks for free from Engineering study Material site. Papadopoulos and C. Air Conditioning is a process used to pull out heat from inside of a closed space, to improve the comfort of the living beings inside. An absorption refrigerator is a refrigerator that uses a heat source e. The principle can also be used to air-condition buildings using the waste heat from a gas turbine or water heater.

Using waste heat from a gas turbine makes the When the working fluid is a gas that is compressed and expanded but does not change phase, the refrigeration cycle is called a gas cycle.

Air is most often this working fluid. As there is no condensation and evaporation intended in a gas cycle, components corresponding to the condenser and evaporator in a vapor compression cycle are the hot and cold gas-to-gas heat exchangers. This is particularly important in these This is particularly important in these times of rapid introduction of alternative refrigerants and the emergence of new technology.

To know more contact team octavesim. These refrigerants do not Refrigerants Solubility of Water contain chlorine. Not all of the refrigerants are recommended at this conditions. The concern of the technician should be how pressures for the same operating conditions. This much water can the refrigerant hold before it becomes should be expected in that each refrigerant is made up free water and causes problems.

Ideally there should not of different chemicals. It is interesting however that the be any moisture in the refrigerant in the system. Proper compression ratio for the refrigerants is not that dis- installation and service techniques should assure that similar. Filter dryers are rated being circulated through the compressor per revolution in drops of water before they become saturated and of the compressor motor.

The Refrigeration Effect is the can no longer hold any additional water. This equates to 6 drops of water before there is free water. This now equates to one drop of water per RA pound of refrigerant. The Density of each refrigerant is different as is the Enthalpy of each refrigerant different. The difference between the two is the percent- much refrigerant in circulation as they did with the CFCs age of each refrigerant in the blend.

The glide is 9. It also lists the types of lubricants recommended respectively. The Enthalpy of these blends is ap- for use with each category. Even though the system may require less issues with the service blends and HFC refrigerants, the refrigerant than the original refrigerant charge, systems proper lubricant approved by Emerson Climate Tech- using a TEV must be recharged to insure a full column nologies, Inc.

Because it is less miscible in mineral Refrigerant 12 is a pure fluid and is categorized as a oil, an approved AB lubricant must be used. The pressures and temperatures in the ditioning. Its basic chemical components are Hydro- The chlorine has been determined to cause the ozone gen, Fluorine, and Carbon.

With the chlorine element depletion. The quickly after that date. The discharge pressure will be higher there- fore the compressors compression ratio will be greater. It has also been very satisfactory for use in two single element compound. Refer to Emerson Climate stage systems for ultra low temperature applications.

Technologies, Inc. Application Engineering Bulletins for It gained popularity for use in the medium temperature the listing of approved lubricants. It has is banned after December 31, Its Ozone Deple- a much greater latent heat of evaporation, and a lower tion Factor is 0.

Where size and economy are critical blend. AB lubricant is recommended for use with this Factor of. In the past, Emerson Climate Technologies, Inc. It is a blend perature applications only. Emerson Climate Technologies, Inc. It can also be used.

The systems pressures multi-stage systems where the vapor temperature can and temperatures will be different. While its latent heat of evaporation is not as high frigerant for low and medium temperature applications. This oc- temperature at a specific pressure. Its glide is 0. If a means, a compressor, is provided to re- of 0.

At its azeotropic rating point it is will not increase, and at the same time liquid refrigerant a true azeotrope. Therefore, refrigerants are always to the refrigerant liquid and the walls of the system. As long as both liquid and vapor are present condensing, saturation temperature, and condensa- in a closed system, and there is no external pressure tion will begin. Heat from the refrigerants latent heat of influence, the refrigerant will evaporate or condense as condensation flows from the system to the surrounding a function of the surrounding temperature.

Evaporation temperature until the pressure in the system is lowered or condensation will continue until the saturation pres- to the equivalent of the saturation pressure of the sur- sure and temperature corresponding to the surrounding rounding temperature. If a means, the compressor, is temperature is reached. When this occurs, heat transfer provided to maintain a supply of hot, high pressure re- will no longer take place. A decrease in the surrounding frigerant vapor, while at the same time liquid refrigerant temperature will allow heat to flow out of the refrigerant.

This will cause the refrigerant to condense and lower the This is the process taking place in a refrigeration and pressure. An increase in the surrounding temperature air conditioning system condenser. This will cause the refrigerant to evaporate, and raise the pressure. Refrigerant gases are soluble pressure is known. Conversely, knowing the refriger- in the lubricant at most temperatures and pressures.

The ants saturation pressure, the refrigerants temperature liquid refrigerant and the lubricant can be completely is known. This generally occurs Presume the refrigerant is enclosed in a refrigeration over a specific range of temperature and composition. If the pressure in the refrigera- off-cycles. It occurs in the compressor sump and other tion system is lowered, the saturation temperature the places such as accumulators, receivers and oil separa- boiling point will be lowered.

The temperature of the tors. In the two phase state, the denser liquid refrigerant liquid refrigerant is now above its boiling point. It will is underneath the less dense lubricant. This separation immediately start to boil absorbing heat. In the process, does not necessarily affect the lubricating ability of the the temperature of the remaining liquid will be reduced.

Those compressors takes place. Heat will now flow into the refrigeration with oil pumps have their pickup low in the crankcase. Accumu- to provide lubrication, a small amount of lubricant is lators, receivers and oil separators also pick up liquid always in circulation with the refrigerant. Lubricant and low in the component. The location and size of the oil refrigerant vapor do not mix readily.

The lubricant can pick up hole is critical. It is imperative that the lubricant be properly circulated through the system only if vapor return to the compressor is not delayed. The industry velocities are high enough to carry the lubricant along. The experience lie on the bottom of refrigeration tubing, decreasing heat with POEs and HFCs has not been as extensive but transfer and possibly causing a shortage of lubricant in has been very successful.

As evaporating temperatures are low- ered, this problem increases. The result is return. Polyol Ester POE lubricants are more polar than One of the basic characteristics of a refrigerant and the mineral oils. This polarity of the POE and HFCs lubricant mixture in a sealed system is the fact that make the two miscible and as such, POE is the lubricant refrigerant is attracted to the lubricant.

The refrigerant to be used with HFC refrigerants. POE lubricants are will vaporize and migrate through the system to the com- synthetic, formed by mixing a specific organic acid with pressor crankcase even though no pressure difference a specific alcohol and subjecting them to a reaction.

The exists. On reaching the crankcase the refrigerant will result is a POE base material and water. The water is condense into the lubricant. This migration will continue driven off and an additive package is mixed with the until the lubricant is saturated with liquid refrigerant.

POE to arrive at a unique approved lubricant. Emerson Further migration will cause the liquid refrigerant to Climate Technologies, Inc. Excess refrigerant in the compressor crankcase can POE lubricants are hygroscopic and want to re-absorb result in violent foaming and boiling action, driving all water. If care is not taken to keep moisture out of the the lubricant from the crankcase causing lubrication system, a chemical reaction can occur and produce problems.

It can also cause slugging of the compres- some weak organic acids. The recommended maximum sor at start up. Should the moisture content rise above PPM, action must be taken to remove Proper piping and system design for the refrigerants the moisture. It is important that the engineer and the and lubricants is critical for the lubricant return. Proper evacuation techniques and the use It is important that the engineer and the service techni- of approved filter-driers with adequate moisture removal cian understand that mineral oil can not be used with capacity is crucial to avoid system problems.

The other refrigerants are of different types and can be an HFC. Application done to achieve a service refrigerant that reacts similarly Engineering Bulletins for a listing of approved lubricants with respect to temperature, pressure and enthalpy as and refrigerants the CFC refrigerant being removed. Its composition is more polar than mineral oil. This refrigeration system, precise and accurate information polar property makes the HCFC service blends more is required.

Like POE, specific ants at any temperature and pressure to be considered. The temperature and pressure columns of these both liquid and vapor, at various temperatures. This consolidates the data the heat content of a substance. In refrigeration practice, into one single table. Table is a typical example of a value. The difference in enthalpy values at different parts of the system are commonly used to determine the perfor- A saturation chart for ready reference is an invaluable mance of a refrigeration unit.

When the heat content per tool for the refrigeration and air conditioning technician pound of the refrigerant entering and leaving a cooling or for anyone checking the performance of a refrigera- coil is determined, the cooling ability of that coil can be tion or air conditioning system.

Suction and discharge calculated provided the refrigerant flow rate is known. From these pressures, the saturated evaporat- Entropy can best be described as a mathematical ing and condensing temperatures can be determined.

It is used in solving Knowing the saturated temperatures makes it easy for complex refrigeration engineering problems. It is not the technician to determine the amount of superheat easily defined or explained. It is seldom used in com- or sub-cooling. For our purpose, the compression process within the compressor is an Isentropic process.

Superheat tables list saturation evaporating temperature and pressure in increments of 1 psi, and tabulate changes in specific volume, enthalpy, and entropy for various increases in temperature of the refrigerant vapor or superheat. Since superheat tables are quite lengthy and are available separately in bound volumes, complete superheat tables have not been included in this manual. The heat rejected may be given off to the eral different processes. In the great majority of applica- ambient air, or in a water cooled system, to the cooling tions, and almost exclusively in the smaller horsepower water.

A change of state from liquid to vapor and back range, the vapor compression system is used for the to liquid allows the refrigerant to absorb and reject large refrigeration process. However, absorption systems are quantities of heat efficiently and repeatedly. In larger equipment, centrifugal systems are used which basically The basic cycle operates as follows: is an adaptation of the compression cycle.

This filter-drier to the metering device. It is at this point that section of this manual will cover only that form of re- the high pressure side of the system is separated from frigeration. There are two pressures existing in a compression system, the evaporating or low pressure, and the con- The TEV controls the quantity of liquid refrigerant be- densing or high pressure. In the Copeland Compli- ing to its pressure.

The boiling action continues until the refrigerant is completely vaporized. Any heat absorbed in the suction refrigerant and the vapor leaving the evaporator. For hermetic and accessible hermetic mo- the expansion valve power element bulb senses this tor-compressors, the heat which must be rejected in temperature, and acts to modulate the feed of refriger- addition to the refrigeration load can be approximated ant through the expansion valve.

Motor watts X The superheated refrigerant vapor leaving the evapora- 3. Volumetric efficiency is defined as the ratio of the actual volume of refrigerant vapor pumped by the compressor As the high pressure high temperature vapor passes to the volume displaced by the compressor pistons. The volumetric efficiency of a piston compressor will In air cooled systems, a fan, and fin-type condenser vary over a wide range, depending on the compressor surface is normally used.

In water cooled systems, a design and the compression ratio. As the temperature of the refrigerant vapor is lowered to the The compression ratio of a compressor is the ratio of saturation temperature corresponding to the high pres- the absolute discharge pressure psia to the absolute sure in the condenser, the vapor condenses into a liquid suction pressure psia.

The refrigerating process is continuous as long as the compressor is operating. Reed compressors have refrigerant vapor as a result of the work energy used in from one to three discharge ports per cylinder to allow the compression process. These discharge is increased and the volume is decreased. The change ports however hold high pressure vapor in them that in pressure and volume tend to maintain equilibrium cannot be sent out to the system.

See Figure To in the perfect gas law equation, so this change alone improve the volumetric efficiency of low temperature would not greatly affect the temperature of the refriger- compressors, the number and size of the discharge ant vapor. In order to compress the refrigerant vapor, ports are reduced. Figure Because the volume work or energy is required.

Following the first law of of refrigerant is less in a low temperature compressor, thermodynamics, this energy cannot be destroyed, and this can be done with little effect on internal pressure all of the mechanical energy necessary to compress the drop but with positive results in increased volumetric vapor is transformed into heat energy.

With the excep- efficiency and compressor capacity. Compressor effi- tion of a small fraction of the total heat given off to the ciency, because of design, is fairly constant for a given compressor body, all of this heat energy is transferred compressor.

Volumetric efficiency will vary inversely to the refrigerant vapor. This causes a sharp increase with the compression ratio. Since it does circulates more pounds of refrigerant therefore delivers not leave the cylinder on the discharge stroke, it re-ex- more BTUs of refrigeration. The higher The second factor is the high temperature of the cylinder the pressure exerted on the residual vapor, the more walls resulting from the heat of compression.

As the dense it becomes, and the greater volume it occupies compression ratio increases, the heat of compression on re-expansion.

This Typical volumetric efficiency curves are shown in Figure reduction in trapped high pressure refrigerant reduces Air Conditioning and refrigeration compressors the amount of re-expansion and increases the com- are designed with a minimum of clearance volume.

The As previously stated, clearance volume is a loss in ac- tual capacity versus theoretical capacity. This results in is more volumetric efficient than an equivalent displace- a consequent loss of volumetric efficiency except for ment, horse power, reed compressor the Scroll compressor.

While the loss of capacity is not as great as that caused by an equivalent decrease in While the volumetric efficiency of each stage of a two suction pressure, it still is severe. When the first pocket of the Scroll temperature must first be reduced to the evaporating closes and captures a volume of refrigerant, all of it temperature in the evaporator before it can start absorb- will be swept along in the compression process and ing heat.

This is accomplished by almost instantaneous discharged out of the Scroll members to the system. Unlike the piston compressor, there is no clearance The latent heat of vaporization involved in the change of area, clearance volume, to create losses. If a portion of this heat and specific volume are inversely proportional, there- could be extracted from the liquid prior to its entry into fore the refrigerant density decreases.

Since a given the evaporator, the effective capacity of the system will compressor's pumping capacity CFH is fixed by its be increased. The loss of capacity with a reduction This can be accomplished by subcooling the liquid re- in suction pressure is extremely rapid. Detailed information as to specific products is available from manufacturers of complete units and accessories.

Used to supplement such literature—and to improve general knowledge of refrigeration—this manual should prove to be very helpful. All rights reserved. By comparison with this standard, the refrigeration or air conditioning with cold and cooling, coldest weather we might ever experience on Earth is yet the practice of refrigeration engineering deals almost much warmer. Cold is really only the ab- Temperature is the scale used to measure the intensity sence of heat, just as darkness is the absence of light, of heat, the indicator that determines which way the and dryness is the absence of moisture.

In the United States, tempera- ture is normally measured in degrees Fahrenheit. Both scales have Thermodynamics is that branch of science dealing several basic points in common, See Figure the with the mechanical action of heat.

There are certain freezing point of water, and the boiling point of water at fundamental principles of nature, often called laws of sea level. On the Fahrenheit scale, Earth. Several of these laws are basic to the study of the temperature difference between these two points is refrigeration. The relation that energy can neither be created or destroyed. It can between Fahrenheit and Celsius scales can always be only be converted from one type to another.

For example, mechanical energy turning a wheel causes friction and is transformed into heat energy. When a vapor such as air or refrigerant is compressed, the compression process is transformed into heat energy and heat is added to the air or refrigerant.

Heat is often defined as energy in motion, for it is never content to stand still. It is always moving from a warm body to a colder body. Much of the heat on the Earth is derived from radiation from the sun. The heat is being transferred from the hot sun to the colder earth.

Heat is transferred from the hot spoon to the colder ice water. The hot coffee transfers both the Fahrenheit and Celsius thermometers are at heat to the colder spoon.

The terms warmer and colder the same point. This is the only point where the two are only comparative. Heat exists at any temperature scales are identical. Using this information, the follow- above absolute zero even though it may be in extremely ing formulas can be used to determine the equivalent small quantities. Fahrenheit or Celsius values. The measurement of temperature has no relation to the quantity of heat. A match flame may have the same Radiation is the transfer of heat by waves similar to light temperature as a bonfire, but obviously the quantity of waves or radio waves.

For example, the sun's energy heat given off is vastly different. A BTU is defined as the amount of heat added or removed to change one pound of wa- ter one degree Fahrenheit.

For example, to raise the temperature of one gallon of water approximately 8. A Calorie is defined as the amount of heat added or removed to change one gram of water One need only step from the shade into direct sunlight one degree Celsius. Another example of radiation is standing in front of a bonfire. The side heat removed. As a result, radiation is of little importance in the The second important law of thermodynamics is that actual refrigeration process.

However, radiation to the heat always travels from a warm object to a colder refrigerated space or product from the outside environ- one. The rate of heat travel is in direct proportion to the ment, particularly the sun, may be a major factor in the temperature difference between the two bodies.

Conduction is the flow of heat through a substance. Actual physical contact is required for heat transfer to take place between two bodies by this means. The heat content of the larger ball is much greater than the small one, but because of the temperature difference, heat will travel from the small ball to the large one See Figure until the temperatures equalize.

Heat is conducted to the other end by the process heat applied, then the water vapor, steam, temperature of conduction. Obviously the fluid during the boiling or evaporating process was absorbing heat. Convection is the flow of heat by means of a fluid me- dium, either vapor or liquid, normally air or water. Air When steam condenses back into water it gives off ex- may be heated by a furnace, and then discharged into actly the same amount of heat that it absorbed during a room to heat objects in the room by convection.

The steam radiator is a common usage of this source of heat. If the water is to be frozen into ice, the same amount of heat that was absorbed in melting must be extracted by some refrigeration process to cause the freezing action. The question arises, just where did those heat units go? Scientists have found that all matter is made up of mol- ecules, infinitesimally small building blocks which are ar- ranged in certain patterns to form different substances. In a solid or liquid, the molecules are very close together.

In a vapor the molecules are much farther apart and move about much more freely. The heat energy that was absorbed by the water became molecular energy, and as a result the molecules rearranged themselves, changing the ice into water, and the water into steam.

Figure When the steam condenses back into water, that same molecular energy is again converted into heat energy. While heat transfer Sensible heat is defined as the heat involved in a change cannot take place without a temperature difference, of temperature of a substance.

When the temperature different materials vary in their ability to conduct heat. Fiberglass has a lot sensible heat content is taking place. The BTUs required of resistance to heat flow and is used as insulation. The amount of heat required to raise the temperature of different substances through Most common substances can exist as a solid, a liquid, a given temperature range will vary.

It requires only. Heat can change and only. Therefore the specific heats Heat is absorbed even though no temperature change of these two substances are. To raise the temperature of one pound of liquid changes to a vapor. It A change of state for a substance from a solid to a liquid, generally exists as a liquid, but can exist in solid form or from a liquid to a solid involves the latent heat of fu- as ice, and as a vapor when it becomes steam. As ice sion. It might also be termed the latent heat of melting, it is a usable form for refrigeration, absorbing heat as or the latent heat of freezing.

If one pound of water at sea level. At the refrig- account. Normally this is calculated by determining the erants boiling point, both liquid and vapor exist simul- percentage of water content in a given product. Since boiling is only a rapid evaporating After a liquid has changed to a vapor, any further heat process, it might also be called the latent heat of boil- added to the vapor raises its temperature.

As long as ing, the latent heat of vaporization, or for the reverse the pressure to which it is exposed remains constant, process, the latent heat of condensation. Since a temperature rise results, sensible heat has been added When one pound of water boils or evaporates, it absorbs to the vapor. To condense one pound of steam to water, ing or saturation point. The air around us is composed BTUs must be extracted from the steam.

The same changes it is said to be superheated. SUBCOOLED LIQUID The absorption of heat by changing a liquid to a vapor, Any liquid that has a temperature lower than the satura- and the discharge of that heat by condensing the vapor tion temperature corresponding to its saturation pres- is the keystone to the whole mechanical refrigeration sure is said to be subcooled.

Water at any temperature process. If it absorbs The weight of substances. The most common example is the use of that atmosphere pressing down on the Earth creates "dry ice" or solid carbon dioxide when used for cooling. At a given The same process can occur with ice below the freez- point, the atmospheric pressure is relatively constant ing point. This process is utilized in some freeze-drying except for minor changes due to changing weather processes at extremely low temperatures and deep conditions.

For purposes of standardization and as a vacuums. The latent heat of sublimation is equal to the basic reference for comparison, the atmospheric pres- sum of the latent heat of fusion and the latent heat of sure at sea level has been universally accepted.

It has evaporation. The condition of temperature and pressure at which At altitudes above sea level, the depth of the atmo- both liquid and vapor can exist simultaneously is spheric blanket surrounding the Earth is less, therefore termed saturation. A saturated liquid or vapor is one the atmospheric pressure is less.

At 5, feet eleva- at its boiling point. For water at sea level, the saturation tion, the atmospheric pressure is only At higher pressures, the saturation inches of mercury.

With a decrease in pressure, the saturation temperature decreases. The micron, a metric Absolute pressure, normally expressed in terms of unit of length, is used for this purpose. When we speak pounds per square inch absolute psia , is defined as of microns in evacuation, we are referring to absolute the pressure existing above a perfect vacuum.

Therefore pressure in units of microns of mercury. Evacuation to microns would be evacuating to an absolute pressure of approximately A pressure gauge is calibrated to read 0 psi regardless. At standard conditions this is the of elevation when not connected to a pressure producing equivalent of a vacuum reading of The absolute pressure of a closed system will cury. At sea level, atmospheric pressure is Pressures below 0 psig are actually negative readings on the gauge, and are usually referred to as The temperature at which a liquid boils is dependent on inches of mercury vacuum.

A refrigeration compound the pressure being exerted on it. The vapor pressure gauge is calibrated in the equivalent of inches of mer- of the liquid is the pressure being exerted by the tiny cury for negative readings. Since Vapor pressure increases with an increase in to 2 inches of mercury on the gauge dial. In the vacuum temperature until at the point when the vapor pressure range, below 0 psig, 2 inches of mercury vacuum is equals the external pressure, boiling occurs.

Table shows rela- pressure. See Table If some means, a compressor tionships existing at various elevations assuming that for example, is used to vary the pressure on the sur- standard atmospheric conditions prevail.

At psig, the boiling point is Table The Water evaporator is a part of a closed system. A pressure can 0 0 The liquid will boil at that tempera- 0 The absolute pressure in inches absorbing heat. This compares to In the United States, density is normally ant vapors may be considered perfect gases, and their expressed in pounds per cubic foot lb.

In this relation- of 1. Although not used in practical refrigeration work, the perfect gas relation is valuable It is frequently necessary to know the pressure created for scientific calculations and is helpful in understanding by a column of liquid, or possibly the pressure required the performance of a refrigerant vapor.

One of the problems of refrigeration is disposing of the heat that has been absorbed during the cooling process. Densities are usually available in terms of pounds per A practical solution is achieved by raising the pressure cubic foot, and it is convenient to visualize pressure in of the vapor so that its saturation or condensing tem- terms of a cube of liquid one foot high, one foot wide, perature will be sufficiently above the temperature of and one foot deep.

Since the base of this cube is the available cooling medium air or water to assure square inches, the average pressure in pounds per efficient heat transfer. This will provide the ability of the square inch is the weight of the liquid per cubic foot di- cooling medium to absorb heat from the refrigerant and vided by For example, water weighs approximately cool it below its boiling point dew point.

When the low Ten feet of water will exert a pressure of 10 X. The same relation of piston. The vapor is discharged as a high pressure high height to pressure holds true, no matter what the area of temperature vapor and is readily condensed because a vertical liquid column. The pressure exerted by other of its high saturation temperature.

A ten foot column exerts a pressure of 4. It then exerts a pressure of. Following foot of lift. The volume of a liquid varies with temperature.

Within the limits of practical re- Fluid head is a general term used to designate any kind frigeration practice, it is regarded as non-compressible. Valves, fittings, sharp bends in the tubing and Table other obstructions also create resistance to flow. The Pressure Equivalents in Fluid Head basic design of the piping system and its installation Pounds Per will determine the pressure required to obtain a given Inches Inches Feet flow rate. If the flow is increased,.

FLUID FLOW Since control of evaporating and condensing pressures For a fluid to flow from one point to another, there must is critical in mechanical refrigeration work, pressure be a difference in pressure between the two points.

Fluids performance of the system. Large pressure drops must may be either liquids or vapors, and the flow of each is be avoided. When designing and installing refrigeration important in refrigeration. Fluid flow through pipes or tubing is governed by the Section 18 in this series of manuals discusses piping pressure exerted on the fluid, the effect of gravity due and proper sizing and installation.

For example, as a faucet is opened, the flow increases even though the pressure in the water main is Heat transfer from a fluid through a tube wall or through constant and the outlet of the faucet has no restriction. As a rule, the greater rate of flow.

Water flows more freely than molasses due the velocity of flow and the more turbulent the flow, the to a property of fluids called viscosity which describes greater will be the rate of heat transfer. Rapid boiling of the fluid's resistance to flow. In oils, the viscosity can an evaporating liquid will also increase the rate of heat be affected by temperatures, and as the temperature transfer.

Quiet liquid flow laminar flow on the other decreases the viscosity increases. They include any fluids which are composed of the cooling media. When the cooling media is involved of more than one component i. Refer to Section 1.

In mechanical refrigeration, a process is required that can transfer large quantities of heat economically and The following definitions apply to dual component mix- efficiently on a continuous basis. From steps in the refrigeration process. Many liquids could be used for absorbing heat through the evaporation process. Unfortunately it boils at temperatures too high for ordinary cooling purposes. It freezes at temperatures An azeotropic refrigerant mixture ARM is a multi-com- too high for low temperature conditions.

A refrigerant ponent which at the azeotropic point does not change must satisfy three main requirements: composition when it evaporates or condenses since both components have exactly the same boiling tem- 1. It must readily absorb heat and change state to a perature at that composition and pressure.