The above figure shows the objectives of refrigerators and heat pumps. It covers the basic principles in refrigeration and is not intended to provide specialized knowledge on the subject. The aim of the book is to provide first degree engineering students with the foundations on refrigeration engineering. An air conditioner works using a thermodynamic cycle called the refrigeration cycle. Mechanical engineering thermodynamics lec 24, pt 2 of 4. As mentioned in the previous chapter, in a typical gas cycle, the working fluid a gas. Carnot cycle pdf explanation and derivation of carnot cycle. It raises the pressure, temperature and enthalpy of the refrigerant by compressing the saturated gas, in an isentropic process, to a superheated. The water leaves the evaporator as a saturated vapour at 10 c. Gas refrigeration cycles include the reversed brayton cycle and the hampsonlinde cycle. To understand the vapor compression cycle, and similar cycles, it is important to understand about the phase changes that a refrigerant goes through.
Refrigeration heat pump cycles are similar to heat engine cycles but they work in reverse and are known as reversed heat engine cycles. Refrigeration and airconditioning systems, when operating under large temperature differences between the condenser and evaporator, consume significant amounts of energy. This sequence runs periodically and always achieves the initial state cyclic process. Refrigeration cycle refrigeration is the transfer of heat from a lower temperature region to a higher temperature region refrigeration cycle is the vaporcompression refrigeration cycle, where the refrigerant is vaporized and condenses alternately and is compressed in the vapor phase. Students who further their studies on refrigeration shall still find this book as. Thermodynamic cycles are broadly classified as power and refrigeration cycles. Simple vapour compression refrigeration system with diagram. Schematic and ts diagram for the actual vaporcompression refrigeration cycle. In those cases, the cycle that best matches the gliding temperature of the sources, the socalled lorenz cycle, is the optimal refrigeration and heatpump cycles. Btu british thermal unit the amount of heat energy required to raise one pound of water one degree fahrenheit. This cycle is often used as a comparison cycle to describe the quality of the cyclic process. A vaporcompression refrigeration cycle with a mechanical subcooling loop to increase system performance and reduce energy consumption is investigated by using both the first and second laws of thermodynamics. The following state variables are required to display a refrigeration cycle in the log ph dia gram. A heat pump uses a vapour compression cycle with refrigerant 12.
Carnot cycle there are only two temperatures in the carnot cycle heat is added at t h heat is rejected at t l there are four temperatures in the otto cycle heat is added over a range of temperatures heat is rejected over a range of temperatures. The heat pump cycle uses an ideal cycle with an evaporator at 5oc and a condenser. In an ideal compressioncompression refrigeration cycle, the refrigerant enters the compressor as a saturated vapour and is cooled to the saturated liquid state in. Thermodynamics and refrigeration cycles clicking on a companys name will take you to their web site. The purpose of a refrigerator is the removal of heat, called the cooling load, from a lowtemperature medium. In practice, the working fluid of the lower cycle is at a higher. It is also used in domestic and commercial refrigerators, largescale warehouses for. Zubair latif comsats institute of information technology, lahore 2.
This digression is designed to help you understand the functional relationship between the components of the refrigeration plant and the thermodynamic processes. For the love of physics walter lewin may 16, 2011 duration. It deals with definition of various terminologies, what are the different forms of refrigeration and their applications, first and second law of thermodynamics, what is temperature, and heat, difference. Refrigeration systems operate on a series of consecutive thermodynamic processes that form a cycle that returns the working substance to the same state.
A typical refrigeration cycle includes, evaporation of the liquid refrigerant, compression of the refrigerant vapor, condensation of the vapor into liquid and finally expansion of the liquid. Carnot refrigerator a refrigeration cycle is a reversed heat engine cycle. Thermodynamics and design principles of refrigeration systems. Power, would produce a refrigeration effect if run backwards in the ts diagram. Simple vapour compression refrigeration system with. In these systems, a fluid called refrigerant absorbs and releases energy in one or multiple thermodynamic cycles. Thermodynamics is the study of energy change rather than the study in absolute values of energy, and the use of arbitrary reference, or datum is acceptable. The first part of the book deals with both the fundamentals of thermodynamics necessary in the study of refrigeration as well as the basics of refrigeration systems. Refrigerators and heat pumps are essentially the same.
The direction of the cyclic process in thets diagram determines w hether this is a heat pump cycle refrigeration cycle or a work machine cycle steam power cycle. Thermodynamics of a vaporcompression refrigeration cycle. Saturated vapor enters the compressor at 100c, and saturated liquid leaves the condenser at 280c. In other words, heat pumps do not work as well in very cold climates as they do in more moderate climates. It has an area on the left grey, in which the operating medium is liquid and supercooled. Refrigeration cycles are anti clockwise and the work represented by the green area is added to the cycle. An actual vapour compression cycle is shown in fig. The lack of consideration of rate processes reduces the usefulness of the carnot. Heat has its own laws, called the laws of thermodynamics.
A vaporcompression refrigeration cycle with a mechanical subcooling loop to increase system performance and reduce energy consumption is investigated by using both the first. The refrigerant aka coolant absorbs heat from inside of your home and then pumps it outside. Heat is transferred from a low temperature level to a higher temperature level. There are two laws that are significant to understand the basic refrigeration cycle and air conditioning. The second law of thermodynamics says that heat can flow from high temperature reservoir to low temperature reservoir only, however, if you want to move the heat from low temperature to high. Refrigeration cycles the vapor compression refrigeration cycle is a common method for transferring heat from a low temperature to a high temperature. The process is shown in a pressureenthalpy diagram. The first point to understand about refrigeration theory is that heat is energy, and it can be made to move. Thus a heat pump may be thought of as a heater if the. Thermodynamic cycle 3 heat pump cycles thermodynamic heat pump cycles are the models for heat pumps and refrigerators. If enough heat is removed from a glass of water, the water will freeze to ice. A refrigeration cycle is a reversed heat engine cycle. Pdf thermodynamics and design principles of refrigeration.
It is also used in domestic and commercial refrigerators, largescale warehouses for chilled or frozen storage of foods and meats. According second law of thermodynamics this requires an external source of energy. For a closed cycle of refrigeration employing the condensable refrigerant vapour, the following processes are required. These topics are presented in a student friendly manner assuming little to no previous knowledge of thermodynamis. Refrigeration is the transfer of heat from a lower temperature region to a higher temperature region. Thermodynamics first law explains that energy cannot be neither created nor destroyed, but can be changed from one form to another. Let us see applications of second law of thermodynamics to automobiles and refrigerators. We here focus on refrigeration cycles more than on the actual components used.
For operating media which can have different phases, such as water or refrigerant, thets diagram looks different. Heat removed from the engine in the cooling system is recovered. Thermodynamics second law can help us better understand how the basic refrigeration cycle works. Refrigeration cycle is the vaporcompression refrigeration. The absorption refrigeration cycle is an alternative that absorbs the refrigerant in a liquid solution rather than evaporating it. Larger is the irreversibility in a refrigeration cycle operating with a given refrigeration load between two fixed temperature levels, larger is the amount of.
Related commercial resource ashrae handbook fundamentals chapter. Calculation using formulae and tables requires a con siderable amount of effort due to the. Another important application of second law of thermodynamics is found in refrigerators and heat pumps, which are based on the principle of reversed carnot cycle or reversed carnot theorem. Analyze the ideal vaporcompression refrigeration cycle. In a cycle, the reduction of work produced by a power cycle or the increase in work required by a refrigeration cycle equals the absolute ambient temperature multiplied by the sum of irreversibilities in all processes in the cycle. A few of the important points of deviations of this cycle as compared to the ideal theoretical cycle are explained below. A heat pump is a mechanical system that allows for the transference of heat from one location the source at a lower temperature to another location the sink or heat sink at a higher temperature. The ordinary vaporcompression refrigeration systems are simple, inexpensive, reliable, and practically maintenancefree. Heat flows in direction of decreasing temperature, i. Page 4 of 4 theory of vapour compression refrigeration cycles carnot cycle this experiment uses a vapour compression refrigeration cycle which cools air down. Most of the time, heat pumps used for heating are considered under the refrigeration heading, since the. The simple vaporcompression refrigeration cycle is the most widely used refrigeration cycle, and it is adequate for most refrigeration applications. The working fluid is a refrigerant that suits the high and low temperature reservoirs temperatures. Clausius statement it is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower.
The second law of thermodynamics is considered to be the most fundamental law of science. Second, it means that heat pumps work best when temperature differences are small. Dec 01, 2016 page 5 of practical vapour compression refrigeration cycle in practice the reverse carnot cycle is adjusted to the vapour compression refrigeration cycle shown below in figure 3. Refrigeration fundamentals heatcraft worldwide refrigeration. The ideal refrigerator like the ideal heat engine operates on a carnot cycle, consisting. Carnot cycle, here the enclosed area is a rectangle. Thermodynamic cycles can be categorized into gas cycles and vapour cycles. If our interest is the heat load, the cycle is called the carnot heat pump. Oct 15, 20 for the love of physics walter lewin may 16, 2011 duration. Since it is a reversible cycle, all four processes can be reversed. Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pumps and refrigerators. Carnot cycle pdfexplanation,derivation of carnot cycle. Both these processes are reversible and therefore it is the most efficient cycle,as it involves no losses.
The difference between the two is that heat pumps are intended to keep a place warm while refrigerators are designed to cool it. It explains not only the working of engines, refrigerators and other equipments used in our daily life, but also highly advanced theories like big bang, expansion of universe, heat death etc. Davis, manager advanced engineering department sundstrand compressors, bristol, virginia introduction air cycle refrigeration has been used in aircraft air conditioning systems for many years. Feb 10, 2016 explains each step in a refrigeration cycle and the energy balance for each step. Thus, the difference in reversible and actual work for any refrigeratio n cycle, theoretical or real, oper. The thermodynamic processes in the refrigeration cycle are complex. The carnot cycle consists of two isothermal processes and two adiabatic processes. Isothermal heat transfer from cold medium to refrigerant evaporator 23. The compressor is driven by a heat engine with a thermal efficiency of 40%. Pdf first and second law analysis of a new power and. How an air conditioner works the refrigeration cycle.
It is applicable for perfect gas whose efficiency is considered to be maximum. Power cycles otto cycle spark ignition diesel cycle brayton cycle gas turbine rankinecycle. When that heat is allowed to move back into the ice, the ice will melt. Unlike the situation with steam power plants it is common practice to begin the design and analysis of refrigeration and heat pump systems by first plotting the cycle on the ph diagram. Nov 22, 2010 energy in the form of heat is required to create a phase change and is the basis of most refrigeration and air conditioning. This is the first module in refrigeration course development and deals with introduction to refrigeration. This amounts to 40% of the energy supplied in the fuel. The cycle as applied in practice, however, differs considerably from the theoretical cycle. Refrigeration fundamentals 2175 west park place blvd. The objective of the book is to serve first degree engineering students with an introduction to refrigeration systems. Introduction a major application area of thermodynamics is refrigeration, which is the transfer of heat from a lower temperature region to a higher temperature one.
Explains each step in a refrigeration cycle and the energy balance for each step. Compression refrigeration cycle the vaporcompression refrigeration is the most widely used cycle for refrigerators, airconditioners, and heat pumps. Once of these laws state that heat always flows from a material at a. Thermodynamics ii chapter 5 refrigeration mohsin mohd sies fakulti kejuruteraan mekanikal, universiti teknologi malaysia. In this article we will discuss about simple vapour compression refrigeration system. Therefore, for the same cooling load, gas refrigeration cycle machines require a larger mass flow rate, which in turn increases their size. An actual vaporcompression refrigeration cycle differs from the ideal one owing mostly to the irreversibilities that occur in various components, mainly due to fluid friction causes pressure drops and heat transfer to or from the surroundings. Though the air is heated and cooled in the air conditioning unit it is the refrigeration cycle using r12 refrigerant as the working fluid which is the main focus of the experiment. Optimalisation of heat transfer rate by pilot control servo ics valve on pulse width modulation. A power cycle or heat engine generates work using an energy source at a high temperature while a refrigeration cycle or heat pump provides cooling from a work input.
In refrigeration and heat pump cycles work is only performed during one stage of the cycle, while. The transfer of heat from a lowtemperature to hightemperature requires a refrigerator andor heat pump. The area inside the loop is negative, meaning there is a. Thermodynamics of airwatercycle airconditioning systems.
A ton of refrigeration or air conditioning is the amount of heat needed to melt one ton of ice in 24 hours. Thermodynamics tutorial 5 heat pumps and refrigeration on completion of this tutorial you should be able to do the following. Energy in the form of heat is required to create a phase change and is the basis of most refrigeration and air conditioning. A thermodynamic refrigeration cycle removes heat from a lowtemperature object refrigeration and rejects it at a higher temperature. The following schematic shows a basic refrigeration or heat pump system with typical property values. Refrigeration cycle 2 thermodynamics of the refrigeration cycle gunt 070 071. The refrigeration cycle can be described by a sequence of state changes of a refrigerant. Refrigeration system an overview sciencedirect topics. Refrigeration cycle it is a well known fact that heat flows in the direction of decreasing temperature, i. Fundamentals of refrigeration thermodynamics by daniel micallef.
Compression refrigeration cycle the vaporcompression refrigeration is the most widely used cycle for. Vapourcompression refrigeration or vaporcompression refrigeration system vcrs, in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for airconditioning of buildings and automobiles. It is a well known fact that heat flows in the direction of decreasing temperature, i. Carefully inspect the unit schematic and the cycle diagram.
In the gas cycle, the refrigeration effect is equal to the product of the specific heat of the gas and the rise in temperature of the gas in the low temperature side. Basic thermodynamics for refrigeration and air conditioning. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counterflow heat exchanger where both streams enter at about 0. This will reverse the direction of heat and work interactions, therefore producing a refrigeration cycle. Me 212 thermodynamics ii chapter 10 examples solution 1 an ideal vaporcompression refrigerant cycle operates at steady state with refrigerant 4a as the working fluid. It does this by changing the pressure and state of the refrigerant to absorb or release heat. Typical topics include refrigeration thermodynamics, refrigeration systems and refrigeration modeling. The most common refrigeration cycle is the vapor compression cycle, which models systems using. The compressor does work on the refrigeration system consumes energy. The vapor compression refrigeration cycle is a common method for transferring heat from a low temperature to a high temperature. A basic vapour cycle consists of isentropic compression, constant pressure cooling, isentropic expansion and constant pressure heating.55 943 1175 1309 506 527 1206 733 1250 1379 528 1012 253 416 638 514 1438 83 1303 169 1061 301 521 721 1195 702 1066 929 1413 337