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Note for Thermodynamics - TD by Nawab Masid

  • Thermodynamics - TD
  • Note
  • USHARAMA COLLEGE OF ENGINEERING - URCE
  • Mechanical Engineering
  • B.Tech
  • 9 Topics
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BASIC THERMODYNAMICS 15ME33 CONTENTS 1. Fundamental Concepts & Definitions 4-11 2. Work and Heat 12-25 3. First Law of Thermodynamics 26-42 4. Second Law of Thermodynamics 43-60 5. Entropy 61-76 6. Pure Substances 77-86 7. Thermodynamic relations 8. Ideal gas mixture Department of Mechanical Engineering, 87-104 105-119 Page 3

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BASIC THERMODYNAMICS 15ME33 UNIT 1 Introduction Thermodynamics involves the storage, transformation, and transfer of energy. Energy is stored as internal energy (due to temperature), kinetic energy (due to motion), potential energy (due to elevation), and chemical energy (due to chemical composition); it is transformed from one of these forms to another; and it is transferred across a boundary as either heat or work. We will present equations that relate the transformations and transfers of energy to properties such as temperature, pressure, and density. The properties of materials thus become very important. Many equations will be based on experimental observations that have been presented as mathematical statements, or laws: primarily the first and second laws of thermodynamics. The mechanical engineer‟s objective in studying thermodynamics is most often the analysis of a rather complicated device, such as an air conditioner, an engine, or a power plant. As the fluid flows through such a device, it is assumed to be a continuum in which there are measurable quantities such as pressure, temperature, and velocity. This book, then, will be restricted to macroscopic or engineering thermodynamics. If the behavior of individual molecules is important, statistical thermodynamics must be consulted. System: We need to fix our focus of attention in order to understand heat and work interaction. The body or assemblage or the space on which our attention is focused is called system. The system may be having real or imaginary boundaries across which the interaction occurs. The boundary may be rigid and sometimes take different shapes at different times. If the system has imaginary boundary then we must properly formulate the idea of system in our mind. Department of Mechanical Engineering, Page 4

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BASIC THERMODYNAMICS 15ME33 Surroundings: Everything else apart from system constitutes surroundings. The idea of surroundings gets formulated the moment we define system. System and surroundings together form what is known as universe. Closed system: If the system has a boundary through which mass or material cannot be transferred, but only energy can be transferred is called closed system. In an actual system, there may not be energy transfer. What is essential for the system to be closed is the inability of the boundary to transfer mass only. Open system: If the system has a boundary through which both energy and mass can transfer, then it is called open system. Isolated System An isolated system is that system which exchanges neither energy nor matter with any other system or with environment. Department of Mechanical Engineering, Page 5

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BASIC THERMODYNAMICS 15ME33 Properties: Variables such as pressure, temperature, volume and mass are properties. A system will have a single set of all these values. Intensive properties: The properties that are independent of amount contained in the system are called extensive properties. For example, take temperature. We can have a substance with varying amount but still same temperature. Density is another example of intensive property because density of water is same no matter how much is the water. Other intensive properties are pressure, viscosity, surface tension. Extensive properties: The properties that depend upon amount contained in the system are called extensive properties. Mass depends upon how much substance a system has in it therefore mass is an extensive property. State: It is defined as condition of a system in which there are one set of values for all its properties. The properties that define the state of a system are called state variables. There is certain minimum number of intensive properties that requires to be specified in order to define the state of a system and this number is uniquely related to the kind of system. This relation is phase rule which we shall discuss little later. Process: The changes that occur in the system in moving the system from one state to the other is called a process. During a process the values of some or all state variables change. The process may be accompanied by heat or work interaction with the system. Equilibrium state: A system is said to be in thermodynamic equilibrium if it satisfies the condition for thermal equilibrium, mechanical equilibrium and also chemical equilibrium. If it is in equilibrium, there are no changes occurring or there is no process taking place. Thermal equilibrium: There should not be any temperature difference between different regions or locations within the system. If there are, then there is no way a process of heat transfer does not take place. Uniformity of temperature throughout the system is the requirement for a system to be in thermal equilibrium. Surroundings and the system may be at different temperatures and still system may be in thermal equilibrium. Mechanical equilibrium: There should not be any pressure difference between different regions or locations within the system. If there are, then there is no way a process of work transfer does not take place. Uniformity of pressure throughout the system is the requirement for a system to be in mechanical equilibrium. Surroundings and the system may be at pressures and still system may be in mechanical equilibrium. Department of Mechanical Engineering, Page 6

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