Heat is the flow of energy from one object or system, to another object or system. This bright hub mechanical technology article looks at the question what is refrigeration and how does this science apply to refrigerators and food items. Refrigeration is the achievement of temperatures below that of the local environment. When we are interested in the heat energy removed from a lowtemperature space, the device is called a refrigerator. Part 2 deals with the applications of refrigeration technology, in the fields of preservation of. Refrigerator working principle the working principle of a refrigerator and refrigeration, in general is very simple.
Thermodynamics is derived from thermo, meaning heat, and dynamics, literally power, and is used to describe the movement or change of a process due to heat flow. These timeaveraged quantities are then used in the normal first and second laws of thermodynamics to derive the relationships between refrigeration power, power input, and thermodynamic properties of the working fluid. Nov 26, 2014 homework statement i have a rectangular pv diagram of a heat engine. Many practical devices are designed to transform energy from one form, such as the heat from burning fuel, into another, such as work. Second, it means that heat pumps work best when temperature differences are small. Mass of the air in a room m500 kg, and its specific heat capacity c714 jkg. Recall that in the carnot cycle heat transfers take place at constant temperature.
Thermodynamics is the branch of physics that studies the transformation of energy. The refrigerator is usually specified as per volumetric capacity on the inside. It also includes the process of maintaining and reducing the temperature of a body below the general temperature of its surroundings. Sign in 4 applications of second law of thermodynamics. The internal energy and temperature of the refrigerant is alternately raised and lowered by the devices in the loop. You breath felt colder when you blow air with lips pursed.
Show the cycle on a ts diagram with respect to saturation lines. Feel the air coming off the back you heat the air outside to cool the air inside see, you cant break even. Impossible refrigerator thermodynamics and pv diagrams. The reversed carnot cycle is the most efficient refrigeration cycle operating between two specified temperature levels. This is a law of physics called the second law of thermodynamics. Thermodynamics and design principles of refrigeration systems.
Heat and temperature are often confused or used interchangeably. The compressor constricts the refrigerant vapour, raising its pressure, and pushes it into the coils on the outside of the refrigerator. Chapters 17 and 18 established two laws of thermodynamics. It covers the basic principles in refrigeration and is not intended to provide specialized knowledge on the subject. Refrigeratordefinition, main parts or component, working. Watervapour condensation is of paramount importance in refrigeration and heat pump systems, because, unlike heating and power applications, cooling. The above figure shows the objectives of refrigerators and heat pumps. Thermodynamics tutorial 5 heat pumps and refrigeration on completion of this tutorial you should be able to do the following. This article is an attempt to simplify these concepts. Therefore, in order to cool a cold body, it is necessary to expend some energy. You will know details about the principal parts of any domestic refrigerator, namely evaporator, compressor, condenser and capillary tube.
Students who further their studies on refrigeration shall still find this book as. Qc is the total cooling load w, and the cop of the refrigerator can be computed using equation 5 that can be attained in 21. Let us see applications of second law of thermodynamics to automobiles and refrigerators. Any two of the properties such as pressure, volume, temperature, internal energy, enthalpy, entropy, much be known to determine the thermodynamic state of the working medium. Have you ever wondered how a refrigerator keeps your food fresh and provides you with a refreshingly chilled beverage in a hot day.
However, simple explanations, although not perfectly accurate, are sufficient to convey the information needed to understand everyday experiences. Pdf abtractthe proper refrigerant flow settings can improve the overall. The other principle at work in a refrigerator is that when you have two things that are different temperatures that touch or are near each other, the hotter surface cools and the colder surface warms up. As i have mentioned in the residential air conditioners section, air conditioning the refrigeration cycle is a process. The first, second, and third law of thermodynamics thlaws05. During this process, the working substance rejects most of its energy to the condenser cooling water. Nov 22, 2010 thermodynamics, as with most concepts in science and physics, is most accurately described using mathematical equations.
In this cycle, a circulating working fluid commonly called refrigerant such as freon enters the compressor as a vapor. Of course a refrigerator is a heat pump in a general meaning in many casesincluding the advanced heating and cooling system for buildingsit is exactly the same mechanism as a refrigerator, but in the technical language of thermodynamics there is an exact difference which relates to what outcome you care about see my answer. In the refrigeration cycle, there are five basic components. The second law of thermodynamics is considered to be the most fundamental law of science. 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. A refrigerator is an insulated box in which low temperature is maintained to facilitate salt or mediumterm storage of food. Work and efficiency as motivation for the development of the second law, we examine two types of processes that. Working of a refrigerator and refrigeration principle behind it is explained with help of animation in a logical way in this video. The main purpose of refrigeration is thermal conditioning e.
The first, second, and third law of thermodynamics. Homework statement i have a rectangular pv diagram of a heat engine. Fundamentals of refrigeration thermodynamics daniel micallef download free. Once of these laws state that heat always flows from a material at a high temperature to a material at a low temperature. Ts diagram and major components for carnot refrigerator. Refrigerator is a device used to cool the bodies to a temperature lower than the temperature of their surrounding.
The second law of thermodynamics with its clausius statement suggests, to throw heat from low temperature to high temperature, one must put extra efforts in the form of work. The compressor constricts the refrigerant vapor, raising its pressure and temperature, and pushes it into the coils of the condenser on the outside of the refrigerator. First we will discuss a quite general form of the rst and second law. Thermodynamics describe processes that involve changes in temperature, transformation of energy, relationship between heat and work from greek, thermos heat,anddynamis power the results of thermodynamics are essential for other fields of physics and for chemistry, chemical engineering, cell biology, biomedical engineering, and materials science. The thermodynamic processes in the refrigeration cycle are. Basic concepts of thermodynamics 3 dependent in some manner on one or more of these fundamental properties. The first law of thermodynamics is an extension of the law of conservation of energy the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. Thermodynamic analysis of an absorption refrigeration system with ionicliquid refrigerant mixture as a working. Thermodynamics second law can help us better understand how the basic refrigeration cycle works. The thermodynamics of the cycle can be analysed on a diagram as shown in figure 2. Working principle of refrigerators how refrigerators work. Well its called thermodynamics and it is here since laws of physics started working.
Basic thermodynamics for refrigeration and air conditioning. The laws of thermodynamics apply to welldened systems. It is more complicated, but i will describe it briefly. As the cool refrigerant gas flows through the chiller cabinet, it absorbs the heat from the food items inside the fridge. Reversed carnot refrigerator and heat pump shown below are the cyclic refrigeration device operating between two constant temperature reservoirs and the ts diagram for the working fluid when the reversed carnot cycle is used. The aim of the book is to provide first degree engineering students with the foundations on refrigeration engineering. Typically the thermodynamic system in a refrigerator analysis will be a working fluid, a refrigerant, that circulates around a loop, as shown in figure 3. It is available in the capacity of 65 liters, 100 liters, 165 liters, 275 liters, to double door refrigerator of capacity as large as. When you pass a lowtemperature liquid close to objects that you want to cool, heat from those objects is transferred to the liquid, which evaporates and takes away the heat in the process.
When the hot gas in the coils of the condenser meets the cooler air temperature of the kitchen, it becomes a liquid. The refrigeration system comprises of various components like freon gas, compressor, condenser, evaporator, thermostat etc, which are all enclosed in a casing. May 24, 2010 homework statement in an isolated room there is a refrigerator. As mentioned in the previous chapter, in a typical gas cycle, the working fluid a. Any two of the properties such as pressure, volume, temperature, internal energy, enthalpy, entropy, much be known to determine the thermodynamic state of the working. Oct 28, 2010 this article explains the construction and working of a domestic home refrigerator. The refrigerant, which is now in a liquid state, passes through the expansion valve and turns into a cool gas due to the sudden drop in pressure.
Thermodynamic cycles can be categorized into gas cycles and vapour cycles. The most commonly used refrigeration machines are the household refrigerator and deep freezer. Fundamentals of refrigeration thermodynamics by daniel micallef. The purpose of a refrigerator is the removal of heat, called the cooling load, from. I have to show why this cannot work in reverse as a refrigerator. Pdf chapter 6 the second law of thermodynamics ruben. Kohlb adepartment of mechanical engineering, washington state university vancouver, 14204 ne salmon creek avenue, vancouver, wa 986869600, usa b school of chemical and biomolecular engineering. A refrigerator is a heat engine operated in reverse, more or less. This article provides the best explanation on the working of a refrigerator in a very. Jan 11, 2014 working of a refrigerator and refrigeration principle behind it is explained with help of animation in a logical way in this video. 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. To move heat from the evaporator to the condenser you need refrigerant, and other mechanical components. Heat pumps, air conditioners, and refrigerators utilize heat transfer from cold to hot.
Again, repeat the same thing but this time try to blow air a little more furiously with your lips pursed what did you observe. According to second law of thermodynamics, it is impossible to have a purely automated machine that can transfer the heat energy from a body at low temperature to a body at high temperature. How does a domestic refrigerator work india study channel. A refrigerator, which operation is based on the reversed camot cycle is called a. Air conditioning is a way to keep your home comfortable by controlling the temperature, air movement, cleanliness, humidity, or dehumidify for our comfort. Refrigeration may be defined as a process of removing heat from a substance and pumping it to the surroundings. Calculate the stream of heat dqdt from the refrigerator assuming its stationary way of work and. This important field of thermodynamics is examined in detail. The pin is all power given to the refrigerator system including. There are two working fluids in an absorption refrigerator, the refrigerant as for a vapourcompression refrigerator, and the carrier, that is the auxiliary liquid that absorbs the refrigerant in the absorber, is pumped up to high pressure, and releases the refrigerant vapours at the generator.
In other words, heat pumps do not work as well in very cold climates as they do in more moderate climates. Refrigeration cycle it is a well known fact that heat flows in the direction of decreasing temperature, i. Refrigeration offers a wide range of applications in machinery and plant. Homework statement in an isolated room there is a refrigerator. The chapter also deals with energy flows in these refrigerators and sources of losses. A refrigerator uses refrigerant4a as the working fluid and operates on an ideal vaporcompression refrigeration cycle between 0. Thermodynamic analysis of an absorption refrigeration. Materials as printouts and additionally also as pdf files. The second law of thermodynamics in this chapter we consider a more abstract approach to heat engine, refrigerator and heat pump cycles, in an attempt to determine if they are feasible, and to obtain the limiting maximum performance available for these cycles. A domestic refrigerator works on vapor compression refrigeration cycle. Saturated vapor enters the compressor at 100c, and saturated liquid leaves the condenser at 280c.