Technology & Engineering
Refrigeration Cycle
The refrigeration cycle is a process used in refrigerators, air conditioners, and heat pumps to transfer heat from one location to another. It involves the compression, condensation, expansion, and evaporation of a refrigerant to absorb heat from a low-temperature area and release it in a high-temperature area. This cycle allows for the cooling of spaces and the preservation of perishable items.
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11 Key excerpts on "Refrigeration Cycle"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 2 Refrigeration Cycles 1. Heat pump and Refrigeration Cycle Thermodynamic heat pump cycles or Refrigeration Cycles are the models for heat pumps and refrigerators. A heat pump is a machine or device that moves heat from one location (the 'source') at a lower temperature to another location (the 'sink' or 'heat sink') at a higher temperature using mechanical work or a high-temperature heat source. Thus a heat pump may be thought of a heater if the objective is to warm an area, or a refrigerator if the objective is to cool an area; regardless the operating principles are identical. Thermodynamic cycles According to the second law of thermodynamics heat cannot spontaneously flow from a colder location to a hotter area; work is required to achieve this. Work is applied to cool a living space or storage volume by pumping heat from a lower temperature heat source into a higher temperature heat sink. The operating principle of the Refrigeration Cycle was described mathematically by Sadi Carnot in 1824 as a heat engine. A heat pump can be thought of as a heat engine which is operating in reverse. Heat pump and Refrigeration Cycles can be classified as vapor compression , vapor absorption , gas cycle , or Stirling cycle types. Vapor-compression cycle The vapor-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems. Figure 1 provides a schematic diagram of the components of a typical vapour-compression refrigeration system. ________________________ WORLD TECHNOLOGIES ________________________ Figure 1: Vapor compression refrigeration The thermodynamics of the cycle can be analyzed on a diagram as shown in Figure 2. In this cycle, a circulating refrigerant such as Freon enters the compressor as a vapor. The vapor is compressed at constant entropy and exits the compressor superheated.
- John Reisel(Author)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Chapter 8 Refrigeration Cycles 342 Summary In this chapter, we have explored the fundamentals of common Refrigeration Cycles. These cycles are used both for cooling a space and for heating a space, with the heating process cycle being termed a heat pump cycle. Other technologies can be used for achieving cooling, such as thermoelectric cooling, evaporative cooling, and radiation cooling. Although all of these technologies are used in some applications, the cycles discussed in this chapter are the most commonly used mechanical refrigeration processes today. PROBLEMS 8.1 A refrigerator is to be used to keep food at a temperature of 28C while placed in a room where the ambient temperature is 218C. (a) Design a basic scheme for the working fluid of a refrigerator that will allow for this process to occur. (b) What is the Carnot coefficient of performance for this situation? 8.2 A freezer, located in a room that has a temperature of 248C, is designed to keep food at –128C. (a) Design a basic scheme for the working fluid of a refrigerator that will allow this process to occur. (b) What is the Carnot coefficient of performance for this situation? 8.3 An air conditioning unit in a building is to cool air inside the building to 20°C while the outdoor air temperature is 32°C. (a) Design a basic scheme for the working fluid of an air Compressor Turbine Hot Heat Exchanger W t Warm Space To Atmosphere Fresh Air Q HHX W c 1 2 3 4 FIGURE 8.14 A component diagram of a reversed Brayton heat pump system. QUESTION FOR THOUGHT/DISCUSSION Under what conditions or for which applications does using a reversed Brayton cycle make sense instead of a vapor-compression Refrigeration Cycle? Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.
No longer available |Learn more- Irving Granet, Maurice Bluestein(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
Analyze the cycle of a reciprocating compressor and determine its volumetric efficiency 14. Calculate the power required to drive a reciprocating compressor 15. Derive the performance index for a heat pump and relate it to the performance index of a Refrigeration Cycle 476 Thermodynamics and Heat Power 16. Show how the performance of a heat pump changes with a change in ambient temperatures 17. Demonstrate that the use of well water or the Earth as a constant-temperature heat source is more desirable than the use of atmospheric air 18. Explain why the use of a heat pump for a given application depends on economic factors more than it does on thermodynamic considerations alone 10.1 Introduction In previous chapters, consideration was given to those cycles that (by the proper placing of elements) could yield useful work from a heat source. By the simple expedient of rear-ranging the sequence of events in these cycles, it is possible (in principle) to remove heat from a region of lower temperature and to deliver it to a region of higher temperature by the input of mechanical work. This removal of heat by the use of mechanical energy has been called the refrigerating effect. In more general terms, refrigeration can be defined as the art of maintaining a body at temperatures below its surroundings or, alternatively, as the removal of heat from a place in which it is undesirable to a place in which it is not. The history of refrigeration can be traced back thousands of years, with natural ice pro-viding the cooling effect desired. The field of refrigeration on a large scale was first devel-oped in the nineteenth century, and in the mid-nineteenth century, the harvesting, storing, and shipping of natural ice became one of the leading industries of the New England states. By the end of the nineteenth century, mechanical refrigeration had become a practical real-ity, and the refrigeration industry as we know it today was in existence.
eBook - PDFHVAC Water Chillers and Cooling Towers
Fundamentals, Application, and Operation, Second Edition
- Herbert W. Stanford III(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
5 Refrigeration Machines Heat flows from hot regions to cold regions, driven by temperature difference and nature’s desire to “level” energy differences (the Third Law of Thermo-dynamics). To reverse this process in a system and move heat from a lower- temperature region to a higher-temperature region requires that “work” be done on the system. Thus, we use refrigeration machines to provide work to move heat from a cooled area and reject it to a hot area. The performance of these machines is usually characterized by a quantity known as the coefficient of performance (COP), defined as COP removed heat input work = Therefore, COP is a dimensionless ratio of how much heat is transferred out of the cooled space to the amount of work that is used to accomplish this task. Unlike typical definitions of “efficiency,” the COP can be larger than unity. Higher values are better, indicating that more heat is removed for a given amount of work. COP is usually dependent on operating conditions, such as the temperatures of the cooled space and the hot space to which heat is to be rejected, and the type of Refrigeration Cycle utilized. All Refrigeration Cycles hinge on one common physical characteristic: if a chemical compound (which we can call a refrigerant ) changes phase from a liquid to a gas, which is called evaporation , the compound must absorb heat to do so. Likewise, if the refrigerant changes phase back from a gas to a liquid, which is called condensation , the absorbed heat must be rejected. Thus, all Refrigeration Cycles depend on circulating a refrigerant between a heat “source” (with heat to be removed, thus resulting in cooling) and a heat “sink” (where the collected heat can be rejected). Overall, there are two basic Refrigeration Cycles in common use: the vapor compression cycle and the absorption cycle . Each of these cycles can be used to cool a secondary refrigerant, usually water, which is then used to cool the spaces in a building.
- S. Bobby Rauf(Author)
- 2021(Publication Date)
- River Publishers(Publisher)
Chapter 11 Refigeration Cycles and HVAC Systems INTRODUCTION Study and understanding of the Basic Refrigeration Cycle, HVAC Systems and Automated HVAC Systems is an essential an integral part of thermodynamics. This chapter provides the reader an opportunity to learn or review important fundamental concepts, principles, analy-sis and computational techniques associated with refrigeration and HVAC systems. The study and exploration of Refrigeration Cycles and HVAC system analysis is illustrated through practical examples, case study and end of the chapter self assessment problems—formulated with the energy engineer’s role in mind. This chapter includes defnitions and explanation of HVAC terms, concepts and mechanical components not introduced before in this text. Defnitions and explanation of several other important HVAC terms and concepts, such as, dry bulb, wet bulb, dew point, enthalpy, specifc enthalpy, humidity ratio, SHR or Specifc Heat Ratio, entropy, saturated liquid, saturated vapor and superheated vapor are covered under Chapter 10 and the preceding material. TYPES OF AIR CONDITIONING SYSTEMS There are several types of air conditioning systems. One could categorize air conditioning systems based on their application and size. The fundamental refrigeration system principles that govern functionality of a refrigerator or chiller versus a typical air condition-ing system are the same. Therefore, most of our discussion and engi-neering analysis in this chapter would apply to all of these devices. Within the air conditioning realm, differences between different types of air conditioning system are premised on their application and size. In large air conditioning systems, such as those pertaining to industrial and commercial applications, major components of the refrigeration systems are sizeable, somewhat independent, and are 229 230 Thermodynamics Made Simple for Energy Engineers located separately.
- Saeed Benjamin Niku, Saeed Benjamin(Authors)
- 2022(Publication Date)
- Springer(Publisher)
95 CHAPTER 4 Thermodynamic Cycles Refrigeration, Air Conditioning, Engines, and Power Cycles 4.1 INTRODUCTION When I was a junior in an engineering college my uncle asked me, "Do you know how a refriger- ator works? Can you repair one?" I replied yes, I know how it works. But whether I can repair one or not depends on a lot of other things. What I meant was that as engineering students, we learn thermodynamics, in which we study the principles that govern how a Refrigeration Cycle works, and based on that we can design the system. However, each company uses somewhat different sets of components to achieve about the same results. Based on experience with those compo- nents, you may or may not be able to fix a broken system or even recognize exactly what a part does; a certified technician can do that better than an engineer. But a technician cannot design the system or create a new one. The same is true with engines. You learn how an engine works and how to design it to ensure that it works properly, but as an engineer, you may or may not know how to fix it depending on your experience. To see this relationship and to understand why it is important to learn the basics and the principles of engineering let's look at refrigeration and power development systems and how the principles and the practical devices map into each other. If you have access to a bicycle pump do the following exercise (if not, a simple balloon will do): Firmly place your finger at the output valve of the pump and press down on the plunger (down-stroke), pressurizing the air inside, and hold it (with the balloon, blow it up and hold the tip to prevent the air from escaping, but do not tie it with a knot). If you touch the body of the pump you will notice that it is a bit warmer (the balloon will most probably not get noticeably warm because of its size).
eBook - PDFRefrigerators, Heat Pumps and Reverse Cycle Engines
Principles, State of the Art and Trends
- Jocelyn Bonjour(Author)
- 2023(Publication Date)
- Wiley-ISTE(Publisher)
Such machines, thanks to the use of the refrigerant latent heat of change of state, make it possible to obtain refrigerating effects per unit mass of fluid that are clearly superior to those of gas systems. The systems are thus smaller in size. 1.1.1. Operation principle of closed-circuit refrigeration installation: definitions As in heat engines, the system considered is a fluid in cyclic evolution. This fluid, which is intended to exchange heat with the sources, is called the refrigerant. If the fluid absorbs the amount of heat from the cold source (CS), it therefore releases to the hot source (HS) (Figure 1.1): Figure 1.1. Thermal generator | | = + [1.1] where is the mechanical (or other) energy received. NOTE.– The purpose of a refrigerator is to extract from the cold source, whereas the purpose of a heat pump is to deliver | | to the hot source. Essentially, these two systems are no different. Heating and Cooling by Reverse Cycle Engines: State of the Art 3 The amount of heat taken at the cold source is called the refrigeration effect or cooling capacity. The ratio = ொ ௐ is called the energy efficiency ratio or coefficient of performance. Let us look for the expression of ε in two different cases: reversible operation and irreversible operation. 1.1.1.1. Reversible operation Like a heat engine, a thermodynamic generator can operate reversibly (internal and external reversibilities) between two thermal sources only if the evolution cycle of the refrigerant is a Carnot cycle. is the maximum temperature and is the minimum temperature (Figure 1.2). Figure 1.2. Carnot engine Heat and work per unit mass of fluid will be denoted by q and w, respectively, expressed in J/kg = , = [1.2] and = | | − = ൫ − ൯ [1.3] 4 Refrigerators, Heat Pumps and Reverse Cycle Engines Therefore: ௧ = [1.4] with being the specific entropy of the fluid expressed in J/kg.K.
eBook - PDFThermodynamics
A Smart Approach
- Ibrahim Dinçer(Author)
- 2020(Publication Date)
- Wiley(Publisher)
7 Refrigeration and Heat Pump Cycles 7.1 Introduction It is well-known that refrigeration has a diverse nature and finds application possibilities in many sectors with a large number of processes ranging from cooling to air conditioning and from food refrigeration to human comfort. The design, analysis, assessment, evalu-ation, and improvement of these systems are of great significance and come down to ther-modynamics. The better one knows thermodynamics the better systems he/she can design for practical applications. As Figure 7.1 illustrates, one person who really knows thermo-dynamics well will design happy refrigeration and heat pump systems. Here, happy sys-tems mean that they are well-designed, -analyzed, -assessed, -evaluated and -improved. So, learning and applying things right to the refrigeration and heat pump systems are really indispensable. That ’ s why this present chapter is important for better systems and applications. It is important to be reminded a couple of conceptual things. When an engineer or an engineering student undertakes the analysis of a refrigeration system and/or a heat pump system, he or she should deal with several basic aspects first, depending upon the type of the problem being studied, that may concern thermodynamics. In conjunc-tion with this, there is a need to introduce several definitions and concepts before mov-ing into refrigeration systems and applications in depth. Furthermore, units are of importance in the analysis of such systems and applications. One should make sure that the units used are consistently to reach the correct result. This means that there are sev-eral introductory factors to be taken into consideration to avoid getting lost. While the information in some situations is limited, it is desirable that the reader comprehend these processes.
- Da-Wen Sun(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
These two terms must be in the same units so that COP is dimensionless. The COP value can be greater than unity, which indicates that the amount of heat removed from the refrigerated area can be greater than the amount of energy input. VAPOR COMPRESSION CYCLE The vapor compression cycle is the most frequently used Refrigeration Cycle in the food industry. The cycle mainly consists of four main components: a compressor, a condenser, an expansion valve, and an evaporator. The evaporator and condenser can be easily identified in a household refrigerator. The freezer compartment used to store frozen foods serves as the evaporator as the heat from the foods is removed by the refrigerant in the evaporator. The condenser is located behind the refrigerator where the coils dissipate heat to the kitchen. Simulation has been widely used for performance prediction and optimum design of the cycle. A recent review has detailed some developing simulation techniques for vapor compression cycles [42]. C ARNOT R EFRIGERATION C YCLE AND I TS M ODIFICATION The Carnot Refrigeration Cycle is the most efficient cycle and therefore is ideal. No other refrig-eration cycles perform better than the Carnot cycle [24]. The cycle 1 ′ -2 ′ -3 ′ -4 ′ shown in Figure 3.3 is the Carnot cycle if there is no temperature difference between T e ′ and the load and no temperature difference between T c ′ and the ambient. Therefore, the Carnot cycle consists of the following thermodynamically reversible processes: adiabatic compression 1 ′ -2 ′ , isothermal rejection of heat 2 ′ -3 ′ , adiabatic expansion 3 ′ -4 ′ , and isothermal addition of heat 4 ′ -1 ′ [25]. Among them, process 4 ′ -1 ′ is the refrigeration step that is the ultimate goal of the cycle as it removes heat from the load; all the other processes serve to achieve this goal by discharging the removed heat to the ambient.
- Paul Anthony Russell, Leslie Jackson, Thomas D. Morton(Authors)
- 2018(Publication Date)
- Reeds(Publisher)
This could be as much as 7.5°K. z The third option is to take no action but this is only an option if the system is operating on guaranteed stock of recycled gas, or if the system will run without maintenance and any failure will not cause a business-critical shut-down until the refrigeration system is replaced. The UK M Notice MGN1819 draws attention to the SI 2002 No. 528 but the latest information can be found in the F-Gas regulations. Tables 7.1 and 7.2 give a good indication of the differences in the properties between the old and the new refrigerant gases. The Vapour Compression System Heat transfer The refrigeration circuit acts as a heat pump by moving the heat from one area to another. The heart of the process is the fact that if the pressure of a fluid is lowered then the volume increases but also the temperature drops. The pressure reduction is completed by the expansion valve and carries on as it passes through the evaporator where it absorbs the heat from its surroundings. Work is carried out on the fluid to raise its pressure again by the compressor and the condenser removes the heat at the higher pressure. The fluid moves to the expansion valve where the process starts again. Refrigeration and Air Conditioning • 295 Operating cycle Where a refrigeration system is critical for the safe operation of the vessel or protection of the cargo or crew such as with the provisions refrigeration system or the LNG cargo refrigeration system, marine practice would require complete duplication of all units. If the system was risk assessed as business critical it would also be singled out for special attention in the maintenance system. A typical refrigeration system is shown in Figure 7.2 and would undertake the following steps during the complete cycle. The refrigerant in its vapour phase is discharged from the compressor at 90°C and is condensed in the condenser at a condensation temperature of 25°C.
eBook - ePub- Ibrahim Dincer(Author)
- 2017(Publication Date)
- Wiley(Publisher)
Furthermore, numerous basic and advanced examples are presented to illustrate how to analyze, assess and evaluate a refrigeration system and investigate how varying operating conditions and state properties affect the performance of the systems. Figure 4.39 Variation of COP with evaporation temperature at various condensation temperature ranges. Courtesy of Colibri b.v.-Stork Thermeq b.v. Nomenclature c p constant pressure specific heat, kJ/kgK ex specific exergy, kJ/kg Energy rate, kW Exergy rate, kW h Specific enthalpy, kJ/kg Mass flow rate, kg/s P Pressure, kPa R Gas constant, kJ/kgK Heat transfer rate, kW s Specific entropy, kJ/kgK S Entropy, kW/K entropy generation rate, kW/K T Temperature, °C or K v Specific volume, m 3 /kg V volume, m 3 Volume flow rate, m 3 /s Work rate or power, kW x Quality X Concentration Greek. Letters η Efficiency Subscripts A absorber C compressor Comp compressor dest destruction e exit E evaporator en energy ex exergy Evap evaporator G generator gen generation H high temperature environment HE heat exchanger i inlet isen isentropic L low temperature environment min minimum p pump R refrigerant rev reversible ss strong solution T turbine th thermal Turb turbine ws weak solution 0 ambient state 1,2... state numbers, equipment numbers Acronym COP Coefficient of Performance Study Problems 4.1 Draw temperature–entropy and pressure–enthalpy. diagrams of an ideal vapor-compression Refrigeration Cycle, and discuss their features. 4.2 Explain the four thermodynamic processes that make up a basic vapor-compression Refrigeration Cycle. 4.3 A Refrigeration Cycle is used to keep a food department at −5 °C in an environment at 20 °C. The total heat gain in the food department is estimated to be 750 kJ/h and the heat rejection in the condenser is 1250 kJ/h
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