Chap 1 - Intro to Thermodynamics - Notes.pdf

Introduction to Thermodynamics CHAPTER 1. Introduction to Thermodynamics N TO THERMODYNAMICS Department of Mechanical & Industrial Engineering, MIT, Manipal Page 1 of 10 ...

Introduction to Thermodynamics CHAPTER 1. Introduction to Thermodynamics N TO THERMODYNAMICS Department of Mechanical & Industrial Engineering, MIT, Manipal Page 1 of 10  Introduction to Thermodynamics TABLE OF CONTENTS CHAPTER 1. Introduction to Thermodynamics........................................................................... 1 Introduction.................................................................................................................................... 3 Thermodynamic Universe.............................................................................................................. 3 Thermodynamic State..................................................................................................................... 6 Thermodynamic Property............................................................................................................... 6 Thermodynamic Process................................................................................................................. 6 Heat Transfer.................................................................................................................................. 6 Numerical on Thermodynamics and Heat Transfer..................... Error! Bookmark not defined. Department of Mechanical & Industrial Engineering, MIT, Manipal Page 2 of 10  Introduction to Thermodynamics Introduction Thermodynamics is a term that was coined by combining two terms:  “Thermo” – heat, thermal energy and temperature changes  “Dynamics” – study of motion, forces and particles Therefore, thermodynamics is the science of energy and its transformation. It deals with energy transfer and its effect on the physical properties of substances. From the smallest cellular organism to the expanse of the universe, the laws of thermodynamics apply to all systems and form the basics of understanding the interactions of the systems with their surroundings. Before we delve into the chapter, it is necessary to understand the technical terms that are used in the world of thermodynamics. Applications of thermodynamics include the following areas:  Power generation plants  Air-conditioning systems  Automobiles  Chemical process industries  Refrigeration systems  Turbines and compressors Thermodynamic Universe A thermodynamic universe consists of a thermodynamic system, surroundings and boundary. A depiction of the same with energy transfer in form of heat and work is shown in Figure 1.1. Figure 1.1 Thermodynamic universe comprising of system, surroundings and boundary.  Thermodynamic System: A thermodynamic system is defined as a quantity of matter or a region in space which is selected for the study. Department of Mechanical & Industrial Engineering, MIT, Manipal Page 3 of 10  Introduction to Thermodynamics  Thermodynamic Surroundings: The mass or region outside the system is called surroundings.  Thermodynamic Boundary: The real or imaginary surfaces which separate the system and surroundings is called boundary. Types of Thermodynamic Systems 1. Open System: A system in which the transfer of both mass and energy takes place is called an open system. This system is also known as control volume. Example: Boiling of water in an open vessel is an example of an open system because the water and heat energy both enter and leaves the boundary of the vessel. Mass Transfer Energy Transfer Figure 1.2 Boiling of water in an open system 2. Closed System: A system in which the transfer of energy but not mass can take place across the boundary is called a closed system. The mass inside the closed system remains constant. Example: Boiling water in a closed vessel. Since the water is boiled in closed vessel the mass of water cannot escape out of the boundary of the system but heat energy continuously entering and leaving the boundary of the vessel. It is an example of a closed system. Department of Mechanical & Industrial Engineering, MIT, Manipal Page 4 of 10  Introduction to Thermodynamics No mass transfer Energy Transfer Figure 1.3 Boiling of water in a closed system 3. Isolated system: A system in which the transfer of mass and energy cannot take place is called an isolated system. Example: Tea present in a thermos flask. In this the heat and the mass of the tea cannot cross the boundary of the thermos flask. Hence the thermos flak is an isolated system. No Mass Transfer No Energy Transfer Figure 1.4 Thermos flask as an example of isolated system Department of Mechanical & Industrial Engineering, MIT, Manipal Page 5 of 10  Introduction to Thermodynamics Thermodynamic State The state of a thermodynamic system is its condition at a specific point in time. It's defined by a set of properties or variables that fully describe the system's condition. In essence, a thermodynamic state is a complete description of a system's condition based on its measurable properties. Thermodynamic Property A measurable physical quantity that helps to define the state of a system. It's like a snapshot of the system at a particular moment. Its value depends solely on the current state of the system, not on how the system got there. Eg: pressure, temperature, viscosity, density etc. Thermodynamic Process A thermodynamic process is a path formed when a system changes its condition from an initial state to a final state. The properties of the system also change when a process takes place. A process involves interaction between a system and its surroundings. Energy can be transferred between the system and surroundings in the form of heat or work. Eg: Isothermal process, isobaric process, adiabatic process etc. Heat Transfer Heat energy is the transfer of energy from a warmer to a cooler space. A difference in temperature causes heat transfer. The transfer takes place until the system reaches equilibrium. There are three primary modes of heat transfer:  Conduction  Convection  Radiation Heat Transfer by Conduction Conduction is the transfer of heat energy from one particle to another within a body or between two bodies in direct contact. It occurs primarily in solids. When a substance is heated, its molecules vibrate more rapidly. These vibrating molecules collide with neighboring molecules, transferring some of their kinetic energy to them. This process continues, with energy passing from molecule to molecule, creating a chain reaction that spreads heat through the material. Heat transfer by conduction depends on factors such as temperature difference, conductivity of the material, thickness and cross-sectional area of the material. Department of Mechanical & Industrial Engineering, MIT, Manipal Page 6 of 10  Introduction to Thermodynamics Eg: A metal rod heated by a candle undergoes heat transfer. The end held over the candle is hot and gradually warms as heat flows to the cold end. Figure 1.5 Heat transfer by conduction in a metal rod Heat Transfer by Convection The transfer of heat energy through the bulk movement of fluids (liquids or gases). It involves the physical movement of the fluid, not individual particles. Natural Convection occurs due to natural buoyancy forces caused by density differences. Examples include a hot air balloon, a boiling pot of water, and ocean currents. Forced Convection occurs when an external force, like a fan or pump, is used to circulate the fluid. Examples include air conditioning systems, car radiators, and computer cooling fans. Figure 1.6 Heat transfer by natural convection Department of Mechanical & Industrial Engineering, MIT, Manipal Page 7 of 10  Introduction to Thermodynamics Heat Transfer by Radiation Radiation is the transfer of heat energy through electromagnetic waves. Unlike conduction and convection, it doesn't require a medium to travel through. Radiation can take place in a vacuum. Any object with a temperature above the absolute zero emits radiation in the form of electromagnetic waves. These waves propagate at the speed of light and can pass through vacuum or transparent medium. When the waves strike an object, they can be absorbed partially, converted to heat and raise the temperature of the object. The factors that affect radiation are the temperature of the object, surface area and surface properties. The hotter an object, the more radiant energy it emits. A larger surface area emits more radiation. Dark, rough surfaces are generally better absorbers and emitters than light, smooth surfaces. Eg: Your hand feels hot when you place it closer to a flame. Figure 1.7 Effect of radiation from a fire on the palm First Law of Thermodynamics The first law of thermodynamics is based on the law of conservation of energy. Law of conservation of energy states that “Energy cannot be created or destroyed; it can only be converted from one form to another”. When energy transfer happens across a system, some amount of energy is always stored in the system. This is called as Stored energy (E) The total energy of an isolated system is a constant. Department of Mechanical & Industrial Engineering, MIT, Manipal Page 8 of 10  Introduction to Thermodynamics Example: In the case of a simple pendulum or a biker going uphill or downhill, the total energy remains the same in each case. The kinetic energy & potential energy increases or decreases with respect to each other to maintain the total energy constant. Friction can also be considered in motion. Figure 1.8 Conservation of energy in a pendulum Figure 1.9 Conservation of energy in a biker going up & down the hill Second Law of Thermodynamics The Second Law of Thermodynamics, unlike the first law which deals with the conservation of energy, is concerned with the direction of energy flow and the quality of energy. It determines the feasibility of a process – if a process will take place or not. In complement to the first law, the second law says that you cannot convert energy into useful work without creating waste heat. The second law is defined by using two statements  Kelvin Planck Statement  Clausius Statement Department of Mechanical & Industrial Engineering, MIT, Manipal Page 9 of 10  Introduction to Thermodynamics Kelvin Planck Statement It is impossible to create a heat engine that works on a cycle, absorbs heat energy and completely converts it into work energy. There will always be some heat rejected to a colder reservoir. Figure 1.10 Second law of thermodynamics applied to a heat engine Clausius Statement It is impossible to create a refrigerator that works on a cycle, transfer heat from cold body to hot body. In simpler terms, heat cannot spontaneously flow from a cold object to a hot object without doing work. Essentially, the Clausius statement establishes the directionality of heat flow and the limitations on heat transfer without external work. Figure 1.11 Second law of thermodynamics applied to a refrigerator ****************************************************** Department of Mechanical & Industrial Engineering, MIT, Manipal Page 10 of 10