Technology & Engineering
Power Cycle
A power cycle refers to the thermodynamic process that converts heat into mechanical work or electricity. It typically involves a fluid, such as water or steam, undergoing various stages of compression, heating, expansion, and cooling to produce power. Power cycles are fundamental to the operation of various energy conversion systems, including steam turbines, gas turbines, and internal combustion engines.
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6 Key excerpts on "Power Cycle"
eBook - PDF- Marc J. Assael, William A. Wakeham, Anthony R. H. Goodwin, Stefan Will, Michael Stamatoudis(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
All of these various machines have at their heart cyclic thermodynamic pro-cesses and it is with the definition of a cycle that we begin. 6.2 WHAT IS A CYCLIC PROCESS AND ITS USE? As the name implies a cyclic process (see Question 1.3.5 for a definition of a thermodynamic process) consist of a series of steps that result in a closed cycle. Power Generation, Refrigeration, and Liquefaction 250 Thus in all characteristic thermodynamic diagrams, such as p as a function of v denoted ( p , v ), temperature as a function of specific entropy ( T, s ), and specific enthalpy as a function of specific entropy ( h, s ), the lines describing the indivi-dual process steps form a closed loop. The term “cyclic process” may refer either to a closed system or to a series of open systems. For a closed system the fluid within the system undergoes a series of proc-esses so that at the end of the cycle the fluid and the system are returned to the initial state. In an open system a fluid flows through a series of mecha-nical components and at the end of the cycle the fluid is returned to its initial thermodynamic state, for example, the fluid in a steam-driven power plant. In some processes, the surroundings are also regarded as one of the system components. This extension applies, for example, to an open-cycle gas-turbine engine, where air initially at ambient temperature flows through the engine components and the air temperature increases, the air is then discharged from the engine to the surroundings, where it mixes with ambient air and the temperature returns to the original ambient value. In this example, the heat exchanger for heat rejection is the air surrounding the engine. Two types of cyclic processes may be distinguished and these are illustrated in Figure 6.1 . In the first process, shown in Figure 6.1a , heat is provided to the system to obtain a net output of work or power.
eBook - PDFThermodynamics
A Smart Approach
- Ibrahim Dinçer(Author)
- 2020(Publication Date)
- Wiley(Publisher)
Heat engines are treated as heat-driven machines that are designed for the efficient conversion of thermal or chemical energy to mechanical or electric energy. The Rankine and the Brayton cycle, or both combined, are considered to be the main power generation cycles used in industry. The Rankine cycle is a steam-driven cycle while the Brayton cycle is a gas-driven cycle. Both cycles convert thermal energy to mechanical energy and electricity. In addition to the categorization of the Power Cycles based on the phase of the working fluid through the cycle, the Power Cycles can also be categorized based whether the cycle is open or closed. Where in open cycles the working fluid is continuously renewed through each cycle, in closed cycles the working fluid is returned to its initial state to be used again in the following cycle. When the Power Cycle takes energy in the heat form and then converts it to power, this type of cycle is referred to as the heat engine. This chapter discusses one of the most important applications of thermodynamics, which is power generation. Power generation is usually achieved by thermodynamics systems that run through a cycle (thermodynamic cycle) and these cycles are referred to as Power Cycles 301 Thermodynamics: A Smart Approach , First Edition. Ibrahim Dincer. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd. since they are used to generate power. The systems or the devices that operates through a thermodynamic cycle are referred to as engines. The Power Cycles can be categorized based on the phase of the working fluid; they are either gas cycles and vapor cycles. Gas cycles are those thermodynamic cycles in which the working fluid remains throughout the cycle in the gaseous phase, while in vapor cycles the working fluid changes phase between the vapor and liquid phases throughout the cycle.
No longer available |Learn more- Irving Granet, Maurice Bluestein(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
The ball is called SOCCKET and utilizes a pendulum-type mechanism inside the ball to provide energy to charge LED lights or batteries. 8.11 Review The stated purpose of this chapter is the study of the conversion of energy from one form to a more useful form. We started our study with a review of the Carnot cycle and then went on to the prototype Rankine, reheat, and regenerative steam cycles. These are “ideal” 417 Vapor Power Cycles cycles in the sense that we ignored irreversible effects such as friction, pressure drops, heat losses, turbulence, and so on. Having studied these cycles, we then turned our attention to the equipment that is used for their practical realization. Many other fluids and cycles using them have been proposed and constructed in addi-tion to those cycles that use either water or gas as their working fluid. Binary fluid cycles using mercury or ammonia and water are examples of such alternates. The direct conversion of the energy of a source to electrical energy without the use of a circulating fluid or moving parts has come under intensive development in recent years. In this chapter, we looked briefly at the thermoelectric converter, fuel cell, thermionic con-verter, MHD generation, solar energy, wind, and nuclear power. Most of these sources are not suitable at present for the large-scale generation of power. However, they are a welcome supplement to our energy supplies and, with further development, will become increasingly economically useful. Cogeneration has recently become a feasible method of energy utilization. By the simple expediency of using the low-temperature energy for process or heating requirements, it is pos-sible to combine electrical energy generation with heat requirements to obtain greater energy utilization than when each requirement is performed separately. While cogeneration does not introduce any new concepts, the savings in energy can be considerable.
eBook - PDFCombined Heating, Cooling & Power Handbook
Technologies & Applications, Second Edition
- Neil Petchers(Author)
- 2020(Publication Date)
- River Publishers(Publisher)
P RACTICE V ERSUS T HEORY Given the frst law of thermodynamics, all of the en-ergy that goes into an operating system is work or heat. The frst law treats heat and work as being interchangeable, though some qualifcations must apply. Work and all other forms of energy can be wholly converted to heat, but the converse is not generally true. The second law of thermodynamics shows that given a source of heat, only a portion of the heat can be con-verted to work in a heat-work cycle. The rest must be re-jected to a heat sink. Thus, it is impossible to have a heat engine that is 100% ef fcient and even the most perfect cycle must be less than perfectly ef fcient. Further, the ideal performance of a given Power Cycle is always less than the Carnot ef fciency. During an ideal (reversible) process, it is theoretically possible to reach the maximum potential ef fciency for the specifc process. Cycle design and opera-tional improvements are initiated in an effort to approach the theoretical limits of the Carnot cycle. There are, how-ever, factors that render the process irreversible. The practical limit of Power Cycle ef fciencies is set by metallurgical limits or strength of available materials (abil-ity to operate under high temperatures and pressures) and by the ambient temperature of the heat sink. In addition, all practical applications of cycles and any other thermal process will be subject to energetic or heat losses resulting from friction, sustained expansion, convection, and con-duction. Thus, reversible thermodynamic processes exist in theory only, defning only the limiting case for heat fow and work processes. From the comparison of reversible and irreversible pro-cesses and cycles, it becomes clear that a critical concern in evaluating various cycles is theoretical and practical cycle ef fciency. Theoretical ef fciency shows the maximum ef-fciency that could, in theory, be attained from any given cycle.
- John Reisel(Author)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
Such requirements usually limit vapor Power Cycles to stationary applications, and also increase the price of the system using the cycle. Gas Power Cycles, on the other hand, typically use a single working fluid that begins as air and is then mixed with fuel. The resulting mixture is burned, resulting in combustion products that then flow through a prime mover to provide power. Finally, the combustion products are exhausted to the atmosphere. The working fluid usually begins as air, so this category of cycles is also known as air Power Cycles. (Although this description fits the common practical form exhibited by gas Power Cycles, the cycles can also be made in a closed-loop format with heat being transferred to some gas flowing through the cycle, and heat being rejected from the gas to the surroundings. This is conceptually similar to how a Rankine cycle is used, but without a phase change in the fluid.) You may observe that this practical operational description does not fit that of a thermodynamic cycle, for which the working fluid begins and ends the cycle in the same thermodynamic state. As such, several assumptions are made to enable these practical systems to be analyzed as thermodynamic cycles. These assumptions permit what is called an air standard cycle (ASC) analysis. The assumptions made for ASC analysis are as follows: 1. The cycle is a closed-loop system with the working fluid being air that flows through the cycle. 2. The air behaves as an ideal gas. 3. All processes in the cycle are internally reversible. 4. The combustion process is replaced with a heat addition process, which receives heat from an external source. 5. The exhaust and intake processes are replaced with a single heat-rejection process which returns the air to its initial state. If a gas other than air is being used, a corresponding gas cycle analysis can be performed, with gas replacing air in the preceding assumptions.
- 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).
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