Pdf comparison of second law efficiency and exergy. Exergy efficiency also known as the secondlaw efficiency or rational efficiency computes the effectiveness of a system relative to its performance in reversible conditions. Enginesandentropy 1st law of thermodynamics 2nd law of thermodynamics heat engines thermal efficiency. Second law of thermodynamics an engine with an efficiency greater than the carnot engine would produce a greater amount of work than the carnot engine, for the same amount of heat input q h. Comparing different energy sources efficiency, amount of fuel. Secondlaw analysis to improve the energy efficiency of. This paper describes various methods of calculating the second law efficiency for a heat pump system using water as a heat source and a heat sink. In short, this principle states that the efficiency of a thermodynamic cycle depends solely on the difference between the hot and cold temperature.
Exergy analysis can clearly indicate the location of energy degradation in a process. The first of these represents the conversion of work into heat. Second law efficiency and is applied to several desalination systems. Exergy and efficiency analysis of combined cycle power plant. Exergy efficiency also known as the second law efficiency or rational efficiency computes the effectiveness of a system relative to its performance in reversible conditions. What is the difference between isentropic efficiency and. Second law of thermodynamics study gtusysllabus,gtu. Second law efficiency thermodynamics questions and answers. Measuring this system using the second law of thermodynamics allows us to see that the initial natural gas input could be used more efficiently and to greater benefit if its heat were not wasted.
Since exergy is a term describing the available work, its inversely proportional to entropy. O satisfying the first law alone does not ensure that the process will take place. Some of this work could be used to run the carnot engine in reverse, returning the heat released by the first engine to the highertemperature reservoir. Second, the engine block cannot be allowed to go over a certain temperature.
The second law of thermodynamics the second law of thermodynamics states that processes occur in a certain direction, not in just any direction. Further, second law efficiency analysis is carried out for condenser and evaporator heat exchangers by varying the effectiveness and number of heat transfer units for different values of inlet temperature to reference the temperature ratio by considering heat transfer irreversibility. First and secondlaw efficiency analysis and ann prediction of a diesel cycle with internal irreversibility, variable specific heats, heat loss. The first law is a special case of the principle of conservation of energy. Second law efficiencies measure how successfully entropy generation has been minimised in a device by comparing real processes to an equivalent idealised isentropic process via their thermal efficiencies or cops are appropriate. Energy, exergy, and second law performance criteria. The second, which is much more useful, concerns the conversion of heat into work. The arrangement is typical of many industrial, commercial, and residential applications, especially those dealing with waste heat recovery.
Second law of thermodynamics answers to questions q22. Exergy balance and second law efficiency for closed systems and steady flow devices duration. Pdf chapter 6 the second law of thermodynamics ruben. The present work analyzed the behaviour of three refrigerants r12, r22, and r407c with variation of evaporator temperature. The second law of thermodynamics can be restated in terms of the carnot cycle, and so what carnot actually discovered was this fundamental law. The second law of thermodynamics the second law of thermodynamics asserts that processes occur in a certain direction and that the energy has quality as well as quantity. Pdf graphical representations of the first and secondlaw effciencies of heat engines, refrigerators and heatpumps are used to compare. One of these is evaluated as the ratio of the sum of the exergy exiting to the sum of the exergy entering. This is lecture number 15 of this lecture series on introduction to aerospace. Note that work does not contribute to the entropy change. Irreversibility, first law efficiency and second law efficiency is given in table 4. Another class of second law efficiencies is composed of task efficiencies. Secondlaw analysis of an ideal otto cycle noam llor and george j.
From exergy analysis, second law efficiency increases with evaporator temperature and. It is impossible for any process to have as its sole result the transfer of heat from a cooler. Pdf first and secondlaw efficiencies in a new thermodynamical. Chapter 5 2 thermal energy reservoir a thermal energy reservoir is a hypothetical body that can supplyor absorbfinite amounts of heat without undergoing any change in temperature large bodies of. Second law of thermodynamics, efficiency, and entropy. And, i put an exclamation mark here, because it seems like a very profound statement. O establishing conditions for equilibrium, o provide means for predicting the direction of processes, o second law is useful. Energy and exergy analysis of boiler and turbine of coal. Work and efficiency as motivation for the development of the second law, we examine two types of processes that concern interactions between heat and work. The second law of thermodynamics institute for energy and. It is defined as the ratio of the thermal efficiency of an actual system compared to an idealized or reversible version of the system for heat engines. Second law analysis of rankine cycle the rankine cycle is not a totally reversible cycle, it is only internally reversible, since heat transfer through a finite temperature difference between the furnace and the boiler or between the condenser and the external medium can results in. A machine that violated the first law would be called a perpetual motion machine of the first kind because it would manufacture its own energy out of nothing and. Different decisions about these lead to different efficiency expressions within the class.
Which of the following statement is true about the first law. The second law provides a criterion for the selection from processes permitted by the first law only of those which occur naturally. The term isentropic efficiency is actually defined for the processes that involves isentropic process in their ideal situations, such as the flow across turbines,nozzles,diffusers and compressors where there is no heat interaction involved in the. Any heat engine employing the carnot cycle is called a carnot engine. Heat and the second law of thermodynamics chapter4great idea. Heat engines and the second law boston university physics. Engineering aims to minimise the generation of entropy. Work and efficiency as motivation for the development of the second law, we examine two types of processes that. Second law efficiency analysis of heat exchangers request pdf.
Thermodynamics thermodynamics the second law of thermodynamics. The first law of thermodynamics asserts that energy must be conserved in any process involving the exchange of heat and work between a system and its surroundings. Jan 31, 2018 exergy balance and second law efficiency for closed systems and steady flow devices duration. The second law is not a deduction from the first law but a separate law of. Or, restated in terms of exergy, no real process can use 100% of the exergy within a system. The minimum power to liquefy the natural gas ng to lng and lpg is from the ideal reversible cycle using exergy difference, which is calculated by equations 58 and 59. Physical processes in nature can proceed toward equilibrium spontaneously. It is defined as the ratio of the minimum cost of producing a product divided by the actual cost of production. Analytical analysis of unbalanced heat exchangers is carried out to study the second law thermodynamic performance parameter through second law efficiency by varying lengthtodiameter ratio for. Chapter heat engines, entropy, and the second law of thermodynamics example.
Comparison of second law efficiency and exergy analysis of. In a sense, the second law implies a definite directionality to the behaviour of. Laws of thermodynamics mit opencourseware free online. To determine the second law efficiency we need both the actual work and the ideal work.
Voiceover the second law of thermodynamics, one statement of it is that the entropy of the universe only increases. The second law states that physical systems tend to slide spontaneously and irreversibly toward a state of disorder a process driven by an increase in entropy. Pdf comparison of second law efficiency and exergy analysis. In 1832, michael faraday reported that the quantity of elements separated by passing an electric current through a molten or dissolved salt is proportional to the quantity of electric charge passed through the circuit. The second law of thermodynamics states that no real process can be completely isentropic. Second law of thermodynamics a process will not occur unless it satisfies boththe first and the second laws of thermodynamics spring 2003 ece309. Visual physics online thermodynamics second law of thermodynamics entropy the second law of thermodynamics is one of the fundamental laws which describes the workings of our universe. The first law places no restriction on the direction of a process, and satisfying the first law. Gases expand from a high pressure to a low pressure.
The internal energy u of a system is increased by the transfer of either heat or work into the system. Second law of thermodynamics no engine, working in a continuous cycle, can take heat from a reservoir at a single temperature and convert that heat completely to work. Not like other laws of physics, it can be stated in many different ways. Exergy efficiency of boiler according to second law analysis and the best exergetic efficiency of the boiler is seen when bituminous coal is used. No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work. Therefore, no engine can have a greater efficiency than a carnot engine operating between the same two temperatures. Exergy efficiency an overview sciencedirect topics. Faradays first and second laws of electrolysis faradays first law of electrolysis from the brief explanation above, it is clear that the flow of current through the external battery circuit fully depends upon how many electrons get transferred from negative electrode or cathode to positive metallic ion or cations.
A machine that violated the first law would be called a perpetual motion machine of the first kind because it would manufacture its own. There are many ways to assess energy system perfor mance, and. The second law efficiency of a heat pump system sciencedirect. The first, second, and third law of thermodynamics. The second law of thermodynamics introduces the notion of entropy s, a measure of system disorder messiness u is the quantity of a systems energy, s is the quality of a systems energy.
Mechanical work a force operated against an opposing force for a distance, the energy transformed is the product of the force times the distance. Second law efficiency is a useful parameter for characterizing the energy requirements of a system in relation to the limits of performance prescribed by the laws of thermodynamics. Energy 32 2007 281296 energy, exergy, and second law performance criteria noam liora, na zhangb adepartment of mechanical engineering and applied mechanics, university of pennsylvania, philadelphia, pa 191046315, usa binstitute of engineering thermophysics, chinese academy of sciences, beijing 80, pr china received 14 october 2005 abstract. Rudyt department of mechanical engineering and applied mechanics, university of pennsylvania, philadelphia, pa 191046315, u. A gas can be heated to the temperature of the bottom of the pond, and allowed to cool as it blows through a turbine. The exergy method is a useful tool for furthering the. Exergy, availability and second law efficiency nptel. Chapter 4 thermodynamics second law of thermodynamics. The exergy term represents the maximum work power that could be done in bringing the geothermal fluid into equilibrium with the surroundings using processes that are completely reversible. Second law of thermodynamics 2nd law nuclear power. This does not conflict with notions that have been observed of the fundamental laws of physics, namely cpt symmetry, since the second law applies statistically, it is hypothesized, on timeasymmetric boundary conditions. This became the basis of the first law of electrolysis. From exergy analysis, second law efficiency increases with evaporator temperature and exergy destruction decreases with increase in. The second law of thermodynamics comes in more than one form, but lets state in a way that makes it obviously true, based on.
Second law of thermodynamics entropy increases, or at best remains constant, in any isolated system. This means that the ratio of its output electric energy to the input heat of combustion of coal is. Pdf first and secondlaw efficiency analysis and ann prediction. Energy 32 2007 281296 energy, exergy, and second law performance criteria noam liora, na zhangb adepartment of mechanical engineering and applied mechanics, university of pennsylvania, philadelphia, pa 191046315, usa. Second law of thermodynamics university of waterloo.
The first law efficiency is defined as the ratio of the output energy to the input energy. In this case the second law is a conservation law with. The second law of thermodynamics is also used in determining the theoretical limits for the performance of commonly used engineering systems, such as heat engines and refrigerators, as well as predicting the degree of completion of chemical reactions. For example, one could use natural gas as a hydrogen source for fuel cells to generate electricity at 60% efficiency second law. But according to the kelvinplanck statement, such an engine would violate the second law of thermodynamics, because there must be losses in the conversion. An ideal heat engine is an imaginary engine in which energy extracted as heat from the hightemperature reservoir is converted completely to work. The second law of thermodynamics is a physical law that is not symmetric to reversal of the time direction. Exergy analysis is based on both first and second law of thermodynamics. Thermodynamics the second law of thermodynamics britannica. Second law efficiency analysis of heat exchangers manjunath. Second law efficiency second law efficiency is a measure of how much of the theoretical maximum carnot you achieve, or in other words, a comparison of the systems thermal efficiency to the maximum possible efficiency. In this paper, an economicsbased second law efficiency is defined by analogy to the exergetic second law efficiency and is applied to several desalination systems. Other sltbased efficiency expressions also appear in the literature. The second law efficiency, equation 57, is used to compare a thermodynamic cycle and an ideal reversible cycle.
Heat engines, entropy, and the second law of thermodynamics. The second law efficiency will always be between the carnot and first law efficiencies. No process is possible in which the sole result is the absorption of heat from a reservoir and its. Second law analysis of an ideal otto cycle noam llor and george j. Boiler exergy analysis, exergy efficiency and destruction, irreversibility. By second law efficiency, i take it youre referring to the exergy efficiency of the heat exchange. The second law efficiency is an indicator of how well the power cycle converts the geothermal fluids exergy, or available energy, to work. Faradays first and second laws of electrolysis electrical4u. Second law analysis of rankine cycle the rankine cycle is not a totally reversible cycle, it is only internally reversible, since heat transfer through a finite temperature difference between the furnace and the boiler or between the condenser and the external medium can results in irreversibilities. Second law of thermodynamics and entropy video khan. As is well known, this efficiency is constrained by the second. In the second law work and heat are treated in an essentially di. Heat is a form of energy that flows from warmer to cooler objects 1st and 2nd law of thermodynamics crucial for understanding all sciences. The investigations present the effects of the evaporating temperatures on the exergy flow losses and second law efficiency and coefficient of performance of a vapour compression refrigeration cycle.
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