Lecture 11 Second Law of Thermodynamics
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Chapter 3. Second and Third Law of Thermodynamics
Chapter 3. Second and third law of thermodynamics Important Concepts Review Entropy; Gibbs Free Energy • Entropy (S) – definitions Law of Corresponding States (ch 1 notes) • Entropy changes in reversible and Reduced pressure, temperatures, volumes irreversible processes • Entropy of mixing of ideal gases • 2nd law of thermodynamics • 3rd law of thermodynamics Math • Free energy Numerical integration by computer • Maxwell relations (Trapezoidal integration • Dependence of free energy on P, V, T https://en.wikipedia.org/wiki/Trapezoidal_rule) • Thermodynamic functions of mixtures Properties of partial differential equations • Partial molar quantities and chemical Rules for inequalities potential Major Concept Review • Adiabats vs. isotherms p1V1 p2V2 • Sign convention for work and heat w done on c=C /R vm system, q supplied to system : + p1V1 p2V2 =Cp/CV w done by system, q removed from system : c c V1T1 V2T2 - • Joule-Thomson expansion (DH=0); • State variables depend on final & initial state; not Joule-Thomson coefficient, inversion path. temperature • Reversible change occurs in series of equilibrium V states T TT V P p • Adiabatic q = 0; Isothermal DT = 0 H CP • Equations of state for enthalpy, H and internal • Formation reaction; enthalpies of energy, U reaction, Hess’s Law; other changes D rxn H iD f Hi i T D rxn H Drxn Href DrxnCpdT Tref • Calorimetry Spontaneous and Nonspontaneous Changes First Law: when one form of energy is converted to another, the total energy in universe is conserved. • Does not give any other restriction on a process • But many processes have a natural direction Examples • gas expands into a vacuum; not the reverse • can burn paper; can't unburn paper • heat never flows spontaneously from cold to hot These changes are called nonspontaneous changes. -
Physics 170 - Thermodynamic Lecture 40
Physics 170 - Thermodynamic Lecture 40 ! The second law of thermodynamic 1 The Second Law of Thermodynamics and Entropy There are several diferent forms of the second law of thermodynamics: ! 1. In a thermal cycle, heat energy cannot be completely transformed into mechanical work. ! 2. It is impossible to construct an operational perpetual-motion machine. ! 3. It’s impossible for any process to have as its sole result the transfer of heat from a cooler to a hotter body ! 4. Heat flows naturally from a hot object to a cold object; heat will not flow spontaneously from a cold object to a hot object. ! ! Heat Engines and Thermal Pumps A heat engine converts heat energy into work. According to the second law of thermodynamics, however, it cannot convert *all* of the heat energy supplied to it into work. Basic heat engine: hot reservoir, cold reservoir, and a machine to convert heat energy into work. Heat Engines and Thermal Pumps 4 Heat Engines and Thermal Pumps This is a simplified diagram of a heat engine, along with its thermal cycle. Heat Engines and Thermal Pumps An important quantity characterizing a heat engine is the net work it does when going through an entire cycle. Heat Engines and Thermal Pumps Heat Engines and Thermal Pumps Thermal efciency of a heat engine: ! ! ! ! ! ! From the first law, it follows: Heat Engines and Thermal Pumps Yet another restatement of the second law of thermodynamics: No cyclic heat engine can convert its heat input completely to work. Heat Engines and Thermal Pumps A thermal pump is the opposite of a heat engine: it transfers heat energy from a cold reservoir to a hot one. -
Physics 100 Lecture 7
2 Physics 100 Lecture 7 Heat Engines and the 2nd Law of Thermodynamics February 12, 2018 3 Thermal Convection Warm fluid is less dense and rises while cool fluid sinks Resulting circulation efficiently transports thermal energy 4 COLD Convection HOT Turbulent motion of glycerol in a container heated from below and cooled from above. The bright lines show regions of rapid temperature variation. The fluid contains many "plumes," especially near the walls. The plumes can be identified as mushroom-shaped objects with heat flowing through the "stalk" and spreading in the "cap." The hot plumes tend to rise with their caps on top; falling, cold plumes are cap-down. All this plume activity is carried along in an overall counterclockwise "wind" caused by convection. Note the thermometer coming down from the top of the cell. Figure adapted from J. Zhang, S. Childress, A. Libchaber, Phys. Fluids 9, 1034 (1997). See detailed discussion in Kadanoff, L. P., Physics Today 54, 34 (August 2001). 5 The temperature of land changes more quickly than the nearby ocean. Thus convective “sea breezes” blow ____ during the day and ____ during the night. A. onshore … onshore B. onshore … offshore C. offshore … onshore D. offshore … offshore 6 The temperature of land changes more quickly than the nearby ocean. Thus convective “sea breezes” blow ____ during the day and ____ during the night. A. onshore … onshore B.onshore … offshore C.offshore … onshore D.offshore … offshore 7 Thermal radiation Any object whose temperature is above zero Kelvin emits energy in the form of electromagnetic radiation Objects both absorb and emit EM radiation continuously, and this phenomenon helps determine the object’s equilibrium temperature 8 The electromagnetic spectrum 9 Thermal radiation We’ll examine this concept some more in chapter 6 10 Why does the Earth cool more quickly on clear nights than it does on cloudy nights? A. -
Fuel Cells Versus Heat Engines: a Perspective of Thermodynamic and Production
Fuel Cells Versus Heat Engines: A Perspective of Thermodynamic and Production Efficiencies Introduction: Fuel Cells are being developed as a powering method which may be able to provide clean and efficient energy conversion from chemicals to work. An analysis of their real efficiencies and productivity vis. a vis. combustion engines is made in this report. The most common mode of transportation currently used is gasoline or diesel engine powered automobiles. These engines are broadly described as internal combustion engines, in that they develop mechanical work by the burning of fossil fuel derivatives and harnessing the resultant energy by allowing the hot combustion product gases to expand against a cylinder. This arrangement allows for the fuel heat release and the expansion work to be performed in the same location. This is in contrast to external combustion engines, in which the fuel heat release is performed separately from the gas expansion that allows for mechanical work generation (an example of such an engine is steam power, where fuel is used to heat a boiler, and the steam then drives a piston). The internal combustion engine has proven to be an affordable and effective means of generating mechanical work from a fuel. However, because the majority of these engines are powered by a hydrocarbon fossil fuel, there has been recent concern both about the continued availability of fossil fuels and the environmental effects caused by the combustion of these fuels. There has been much recent publicity regarding an alternate means of generating work; the hydrogen fuel cell. These fuel cells produce electric potential work through the electrochemical reaction of hydrogen and oxygen, with the reaction product being water. -
Recording and Evaluating the Pv Diagram with CASSY
LD Heat Physics Thermodynamic cycle Leaflets P2.6.2.4 Hot-air engine: quantitative experiments The hot-air engine as a heat engine: Recording and evaluating the pV diagram with CASSY Objects of the experiment Recording the pV diagram for different heating voltages. Determining the mechanical work per revolution from the enclosed area. Principles The cycle of a heat engine is frequently represented as a closed curve in a pV diagram (p: pressure, V: volume). Here the mechanical work taken from the system is given by the en- closed area: W = − ͛ p ⋅ dV (I) The cycle of the hot-air engine is often described in an idealised form as a Stirling cycle (see Fig. 1), i.e., a succession of isochoric heating (a), isothermal expansion (b), isochoric cooling (c) and isothermal compression (d). This description, however, is a rough approximation because the working piston moves sinusoidally and therefore an isochoric change of state cannot be expected. In this experiment, the pV diagram is recorded with the computer-assisted data acquisition system CASSY for comparison with the real behaviour of the hot-air engine. A pressure sensor measures the pressure p in the cylinder and a displacement sensor measures the position s of the working piston, from which the volume V is calculated. The measured values are immediately displayed on the monitor in a pV diagram. Fig. 1 pV diagram of the Stirling cycle 0210-Wei 1 P2.6.2.4 LD Physics Leaflets Setup Apparatus The experimental setup is illustrated in Fig. 2. 1 hot-air engine . 388 182 1 U-core with yoke . -
Thermodynamics of Power Generation
THERMAL MACHINES AND HEAT ENGINES Thermal machines ......................................................................................................................................... 1 The heat engine ......................................................................................................................................... 2 What it is ............................................................................................................................................... 2 What it is for ......................................................................................................................................... 2 Thermal aspects of heat engines ........................................................................................................... 3 Carnot cycle .............................................................................................................................................. 3 Gas power cycles ...................................................................................................................................... 4 Otto cycle .............................................................................................................................................. 5 Diesel cycle ........................................................................................................................................... 8 Brayton cycle ..................................................................................................................................... -
Power Plant Steam Cycle Theory - R.A
THERMAL POWER PLANTS – Vol. I - Power Plant Steam Cycle Theory - R.A. Chaplin POWER PLANT STEAM CYCLE THEORY R.A. Chaplin Department of Chemical Engineering, University of New Brunswick, Canada Keywords: Steam Turbines, Carnot Cycle, Rankine Cycle, Superheating, Reheating, Feedwater Heating. Contents 1. Cycle Efficiencies 1.1. Introduction 1.2. Carnot Cycle 1.3. Simple Rankine Cycles 1.4. Complex Rankine Cycles 2. Turbine Expansion Lines 2.1. T-s and h-s Diagrams 2.2. Turbine Efficiency 2.3. Turbine Configuration 2.4. Part Load Operation Glossary Bibliography Biographical Sketch Summary The Carnot cycle is an ideal thermodynamic cycle based on the laws of thermodynamics. It indicates the maximum efficiency of a heat engine when operating between given temperatures of heat acceptance and heat rejection. The Rankine cycle is also an ideal cycle operating between two temperature limits but it is based on the principle of receiving heat by evaporation and rejecting heat by condensation. The working fluid is water-steam. In steam driven thermal power plants this basic cycle is modified by incorporating superheating and reheating to improve the performance of the turbine. UNESCO – EOLSS The Rankine cycle with its modifications suggests the best efficiency that can be obtained from this two phaseSAMPLE thermodynamic cycle wh enCHAPTERS operating under given temperature limits but its efficiency is less than that of the Carnot cycle since some heat is added at a lower temperature. The efficiency of the Rankine cycle can be improved by regenerative feedwater heating where some steam is taken from the turbine during the expansion process and used to preheat the feedwater before it is evaporated in the boiler. -
Thermodynamic Entropy As an Indicator for Urban Sustainability?
Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 00 (2017) 000–000 www.elsevier.com/locate/procedia Urban Transitions Conference, Shanghai, September 2016 Thermodynamic entropy as an indicator for urban sustainability? Ben Purvisa,*, Yong Maoa, Darren Robinsona aLaboratory of Urban Complexity and Sustainability, University of Nottingham, NG7 2RD, UK bSecond affiliation, Address, City and Postcode, Country Abstract As foci of economic activity, resource consumption, and the production of material waste and pollution, cities represent both a major hurdle and yet also a source of great potential for achieving the goal of sustainability. Motivated by the desire to better understand and measure sustainability in quantitative terms we explore the applicability of thermodynamic entropy to urban systems as a tool for evaluating sustainability. Having comprehensively reviewed the application of thermodynamic entropy to urban systems we argue that the role it can hope to play in characterising sustainability is limited. We show that thermodynamic entropy may be considered as a measure of energy efficiency, but must be complimented by other indices to form part of a broader measure of urban sustainability. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the Urban Transitions Conference. Keywords: entropy; sustainability; thermodynamics; city; indicators; exergy; second law 1. Introduction The notion of using thermodynamic concepts as a tool for better understanding the problems relating to “sustainability” is not a new one. Ayres and Kneese (1969) [1] are credited with popularising the use of physical conservation principles in economic thinking. Georgescu-Roegen was the first to consider the relationship between the second law of thermodynamics and the degradation of natural resources [2]. -
The Aircraft Propulsion the Aircraft Propulsion
THE AIRCRAFT PROPULSION Aircraft propulsion Contact: Ing. Miroslav Šplíchal, Ph.D. [email protected] Office: A1/0427 Aircraft propulsion Organization of the course Topics of the lectures: 1. History of AE, basic of thermodynamic of heat engines, 2-stroke and 4-stroke cycle 2. Basic parameters of piston engines, types of piston engines 3. Design of piston engines, crank mechanism, 4. Design of piston engines - auxiliary systems of piston engines, 5. Performance characteristics increase performance, propeller. 6. Turbine engines, introduction, input system, centrifugal compressor. 7. Turbine engines - axial compressor, combustion chamber. 8. Turbine engines – turbine, nozzles. 9. Turbine engines - increasing performance, construction of gas turbine engines, 10. Turbine engines - auxiliary systems, fuel-control system. 11. Turboprop engines, gearboxes, performance. 12. Maintenance of turbine engines 13. Ramjet engines and Rocket engines Aircraft propulsion Organization of the course Topics of the seminars: 1. Basic parameters of piston engine + presentation (1-7)- 3.10.2017 2. Parameters of centrifugal flow compressor + presentation(8-14) - 17.10.2017 3. Loading of turbine blade + presentation (15-21)- 31.10.2017 4. Jet engine cycle + presentation (22-28) - 14.11.2017 5. Presentation alternative date Seminar work: Aircraft engines presentation A short PowerPoint presentation, aprox. 10 minutes long. Content of presentation: - a brief history of the engine - the main innovation introduced by engine - engine drawing / cross-section - -
Carnot Cycles
CARNOT CYCLES Sadi Carnot was a French physicist who proposed an “ideal” cycle for a heat engine in 1824. Historical note – the idea of an ideal cycle came about because engineers were trying to develop a steam engine (a type of heat engine) where they could reject (waste) a minimal amount of heat. This would produce the best efficiency since η = 1 – (QL/QH). Carnot proposed that a cycle comprised of completely (internally and externally) reversible processes would give the maximum amount of net work for a given heat input, since the work done by a system in a reversible (ideal) process is always greater than that in an irreversible (real) process. THE CARNOT HEAT ENGINE CYCLE CONSISTS OF FOUR REVERSIBLE PROCESSES IN A SEQUENCE: 1 Æ 2: Reversible isothermal expansion. Heat transfer from HTR (+) and boundary work (+) occur in closed system 2 Æ 3: Reversible adiabatic expansion Work output (+), but no heat transfer 3 Æ 4: Reversible isothermal compression Heat transfer (-) and boundary work (-) occur in closed system 4 Æ 1: Reversible adiabatic compression Work input (-), but no heat transfer AND Wout >>> Win 1 P-V DIAGRAM FOR CARNOT HEAT ENGINE CYCLE P 1 2 4 3 Showing net work is POSITIVE. V A useful example of an isothermal expansion is boiling (vaporization) at a constant pressure in a device such as a piston-cylinder. Similarly, an example of an isothermal compression is condensation at a constant pressure in a piston-cylinder. Also, heat transfer can only occur in processes 1 Æ 2 and 3 Æ4. 1 Æ 2: since work is positive (expansion) and Δu is positive (e.g., boiling) then heat transfer is positive (input from HTR). -
The Concept of Irreversibility: Its Use in the Sustainable Development and Precautionary Principle Literatures
The Electronic Journal of Sustainable Development (2007) 1(1) The concept of irreversibility: its use in the sustainable development and precautionary principle literatures Dr. Neil A. Manson* *Dr. Neil A. Manson is an assistant professor of philosophy at the University of Mississippi. Email: namanson =a= olemiss.edu (replace =a= with @) Writers on sustainable development and the Precautionary Principle frequently invoke the concept of irreversibil- ity. This paper gives a detailed analysis of that concept. Three senses of “irreversible” are distinguished: thermody- namic, medical, and economic. For each sense, an ontology (a realm of application for the term) and a normative status (whether the term is purely descriptive or partially evaluative) are identified. Then specific uses of “irreversible” in the literatures on sustainable development and the Precautionary Principle are analysed. The paper concludes with some advice on how “irreversible” should be used in the context of environmental decision-making. Key Words irreversibility; sustainability; sustainable development; the Precautionary Principle; cost-benefit analysis; thermody- namics; medicine; economics; restoration I. Introduction “idea people” as a political slogan (notice the alliteration in “compassionate conservatism”) with the content to be The term “compassionate conservatism” entered public provided later. The whole point of a political slogan is to consciousness during the 2000 U.S. presidential cam- tap into some vaguely held sentiment. Political slogans paign. It was created in response to the charge (made are not meant to be sharply defined, for sharp defini- frequently during the Reagan era, and repeated after the tions draw sharp boundaries and sharp boundaries force Republican takeover of Congress in 1994) that Repub- undecided voters out of one’s constituency. -
Lecture 10. Heat Engines (Ch. 4)
Lecture 11. Heat Engines (Ch. 4) A heat engine – any device that is capable of converting thermal energy (heating) into mechanical energy (work). We will consider an important class of such devices whose operation is cyclic. Heating – the transfer of energy to a system by thermal contact with a reservoir. Work – the transfer of energy to a system by a change in the external parameters (V, el.-mag. and grav. fields, etc.). The main question we want to address: what are the limitations imposed by thermodynamic on the performance of heat engines? Perpetual Motion Machines are Impossible Perpetual Motion Machines of the first type – these designs seek to violation of the First Law create the energy required for their (energy conservation) operation out of nothing. Perpetual Motion Machines of the second type - these designs extract the energy required for their operation violation of the Second in a manner that decreases the entropy Law of an isolated system. hot reservoir Word of caution: for non-cyclic processes, T H 100% of heat can be transformed into work without violating the Second Law. heat Example: an ideal gas expands isothermally work being in thermal contact with a hot reservoir. Since U = const at T = const, all heat has been transformed into work. impossible cyclic heat engine Fundamental Difference between Heating and Work - is the difference in the entropy transfer! Transferring purely mechanical energy to or from a system does not (necessarily) change its entropy: ΔS = 0 for reversible processes. For this reason, all forms of work are thermodynamically equivalent to each other - they are freely convertible into each other and, in particular, into mechanical work.