Fundamental Concept of Thermal Engineering/Thermodynamics, Lecture notes of Thermal Engineering

Download Fundamental Concept of Thermal Engineering/Thermodynamics and more Lecture notes Thermal Engineering in PDF only on Docsity! Fall 2019, NAME-7 Course Code: NAME 177 Course Title: Thermal Engineering Course Teacher: Md Daluar Hussain Sumon Lecturer, Department of NAME, MIST Fundamental Concepts of Thermal Engineering ae __ Father of Thermodynamics — 1/6/2022 D.H. SUMON What is Thermal Engineering? ➢ The field of engineering science which deals with application of thermodynamics and it’s law to work producing / work absorbing devices; in order to understand their function and improve their performance. ➢ It includes heat transfer, thermodynamics , form of energy and their sources, energy transfer, energy conversion and HAVAC applications. 11/6/2022 5D.H. SUMON Thermal Engineering: Application Areas ➢Home appliances – electric/gas ranges, refrigerator, pressure cooker, water heater, air conditioner, etc. ➢ Industrial appliances—pumps, compressor, steam generators, furnaces, heat exchangers, HVAC system, etc. ➢Power Systems—automobiles, jet engines, power plants, etc. ➢Electronic cooling—computers, TV, etc. 11/6/2022 6D.H. SUMON 1/6/2022 Refrigerator © McGraw-Hill Education, Jill Braaten Power plants Human body © Malcolm Fife/Getty Images RF © Ryan McVay/Getty Images RF Wind turbines Food processing © F. Schussler/PhotoLink/Gepy H, SUMON¢!ow Images RF Images RF Aircraft and spacecraft © PhotoLink/Getty Images RF Cars © Mark Evans/Getty Images RF A piping network in an industrial facility. Courtesy of UMDE Engineering Contracting 11/6/2022 10 Classification of System Basically, there are three types of systems: ➢ Open system ➢ Closed system and ➢ Isolated system Various Types of Boundaries D.H. SUMON Classification of System ➢Closed system: A closed system (also known as a control mass) consists of a fixed amount of mass, and no mass can cross its boundary. That is, no mass can enter or leave a closed system. Example: a piston-cylinder assembly filled with gas. ➢But energy, in the form of heat or work, can cross the boundary; the matter may also change in chemical composition within the boundaries. ➢The volume of a closed system does need to be fixed. 11/6/2022 11D.H. SUMON 11/6/2022 12 Classification of System ➢An open system, or a control volume, is a properly selected region in space for which both mass and energy (heat and work) may cross the boundary. Example: Flow through nozzle, compressor, turbine. ➢The boundaries of a control volume are called a control surface. D.H. SUMON Properties of a System ➢A thermodynamic property is any characteristic of a system by which its physical condition may be described. Its numerical value depends only on the (local) thermodynamic equilibrium state of the system and is independent of the path (that is, the prior history how that state was attained). Example: Some familiar properties: pressure P, temperature T, volume V, mass m. less familiar ones : viscosity, modulus of elasticity, electric resistance. ➢Any characteristic which identify state of a system is called property. 11/6/2022 15D.H. SUMON Classification of Properties 11/6/2022 16 1. Intensive properties ➢Intensive properties are those that are independent of the extent or mass of a system. Example: Temperature T, pressure P, density ρ, velocity v, chemical concentration etc. ➢If a single phase system is divided arbitrarily into n parts, then the value of a given intensive property will be the same for each of the n subsystems. Thus intensive properties have the same value throughout a system in equilibrium. ➢If the system is not in equilibrium, the property vary from place to place within the system at any moment [may be functions of both position & time]. D.H. SUMON Classification of Properties 17 2. Extensive properties ➢Extensive properties are those whose values depend on the size or extent of the homogeneous system.. Example: Total mass m, total volume V, total momentum, Energy E and the quantity of electric charge etc. ➢May change with time. ➢A property is extensive if its value for the whole system is the sum of its values for the various subsystems or parts. If a system is divided into n(possibly unequal) parts, then the extensive property Y for the whole system is ➢Generally, uppercase letters are used to denote extensive properties (with mass m being a major exception), and lowercase letters are used for intensive properties (with pressure P and temperature T being the obvious exceptions). State, Process & Cycle 11/6/2022 20 Figure: Three process paths that change the state of the system from A to B. D.H. SUMON Classifications Cycle 11/6/2022 21 Types of process based on path change of the state: ➢Cyclic process - when a system in a given initial state goes through various processes and finally return to its initial state, the system has undergone a cyclic process or cycle. ➢Reversible process - it is defined as a process that, once having take place it can be reversed. In doing so, it leaves no change in the system or boundary. ➢ Irreversible process -a process that cannot return both the system and surrounding to their original conditions D.H. SUMON Equilibrium ➢A state of balance—there is no unbalance potential (P, T) within a system. ➢Properties are truly defined when a system is in equilibrium ➢A system in equilibrium experiences no changes with time when it is isolated from its surroundings. Hence a system in equilibrium cannot change in state without an interaction with its surroundings. 11/6/2022 22D.H. SUMON Quasi-static/ Quasi Equilibrium Process ➢ In thermodynamics, a quasi-static process is a thermodynamics process that happens slowly enough for the system to remain in internal equilibrium. ➢ The deviation from thermodynamic equilibrium is infinitesimal in quasi static process. ➢ An example of this is quasi-static compression, where the volume of a system changes at a rate slow enough to allow the pressure to remain uniform and constant throughout the system. ➢ All states of the system passes through are equilibrium states. 11/6/2022 25D.H. SUMON Non Quasi-static/Non- Equilibrium Process ➢A non quasi-static process/ non equilibrium process is a thermodynamics process where the initial and final state remain equilibrium but internal sates are not in equilibrium. ➢All states of the system passes through are no-equilibrium states ➢All natural processes occurring in the universe are irreversible and non-quasi-static. 11/6/2022 26D.H. SUMON Energy Transport Mechanism 11/6/2022 27 There are three energy transport mechanisms, any or all of which may be operating in any given system: 1. heat, 2. Work and 3. mass flow. ➢The sign conventions for heat and work are not the same. ➢Heat transfer into a system is taken as positive, whereas work must be produced by or come out of a system to be positive Sign convention: W >0 (+ve), Work done by the system W<0 (-ve), Work done on the system Q>0 (+ve), Heat transfer to the system Q<0 (-ve), Heat transfer from the system D.H. SUMON Specific Heat, Enthalpy & Entropy ➢ Heat is also a transient quantity, which transfer across the boundary when a system changes its state due to difference in temperature between the system and surroundings. ➢ The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius Heat Required Q = m c (T2-T1) c=specific heat ➢ Two types of heating process: i. Specific heat at constant pressure (CP) ii. Specific heat at constant volume (Cv) 11/6/2022 30D.H. SUMON Specific Heat, Enthalpy & Entropy ➢Enthalpy is a property of a thermodynamic system ➢ It is a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume. Enthalpy, H=U+PV ➢Entropy is a thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system. 11/6/2022 31D.H. SUMON