Thermodynamic Concept PDF

Thermodynamic concept Open system Thermodynamic concept Thermodynamic & Energy Thermodynamics Is a branch of natural science concerned with heat and temperature and their relation to energy and work. It defines macroscopic variables, such as internal energy, entropy, and pressure that partly describ...

Thermodynamic concept Open system Thermodynamic concept Thermodynamic & Energy Thermodynamics Is a branch of natural science concerned with heat and temperature and their relation to energy and work. It defines macroscopic variables, such as internal energy, entropy, and pressure that partly describe a body of matter or radiation. Energy Is the capacity to do work or the ability to cause change. Conservation of energy principle: In physics, the law of conservation of energy states that the total energy of an isolated system cannot change-it is said to be conserved over time. Energy can be neither created nor destroyed, but can change form, Thermodynamic concept Thermodynamic & Energy A thermodynamic system Is a precisely specified macroscopic region of the universe, defined by boundaries or walls of particular natures, together with the physical surroundings of that region, which determine processes that are allowed to affect the interior of the region, studied using the principles of thermodynamics. System: A quantity of matter or a region in space chosen for study. Surrounding: The region outside the system Boundary: The real or imaginary surface that separates the system from it surrounding.(fixed or movable). Thermodynamic concept Thermodynamic & Energy Fig: show the system, surrounding, and boundary Thermodynamic concept Thermodynamic & Energy Closed and Open system: Open system: matter may flow in and out of some segments of the system boundaries. There may be other segments of the system boundaries that pass heat or work but not matter. Respective account is kept of the transfers of energy across those and any other several boundary segments Thermodynamic concept Thermodynamic & Energy Closed and Open system: Flow process The region of space enclosed by open system boundaries is usually called a control volume. It may or may not correspond to physical walls. It is convenient to define the shape of the control volume so that all flow of matter, in or out, occurs perpendicular to its surface. One may consider a process in which the matter flowing into and out of the system is chemically homogeneous. Thermodynamic concept Thermodynamic & Energy Fig: show both Mass & Energy can cross the boundaries of control volume Thermodynamic concept Thermodynamic & Energy Closed and Open system: Closed system: No mass may be transferred in or out of the system boundaries. The system always contains the same amount of matter, but heat and work can be exchanged across the boundary of the system. Whether a system can exchange heat, work, or both is dependent on the property of its boundary. Thermodynamic concept Thermodynamic & Energy Closed and Open system: Closed system: Adiabatic boundary - not allowing any heat exchange: A thermally isolated system Rigid boundary - not allowing exchange of work: A mechanically isolated system Thermodynamic concept Thermodynamic & Energy Closed and Open system: Isolated system : Is an idealized system that has no interaction with its surroundings. It is not customary to ask how its state is detected empirically. Ideally it is in its own internal thermodynamic equilibrium when its state does not change with time Thermodynamic concept Thermodynamic & Energy Fig: Mass cannot cross the boundary of closed system but energy can Thermodynamic concept Thermodynamic & Energy Fig: show the isolated system Thermodynamic concept Thermodynamic & Energy Interactions of thermodynamic systems: Type of system Open Closed Thermally isolated Mechanically isolated Isolated Mass flow Work Heat Thermodynamic concept Thermodynamic & Energy Thermodynamic concept Thermodynamic & Energy Property of the system: Any characteristic of a system is called property. Like Pressure P , Temperature T , Volume V, and Mass m. The list can be extended to include less familiar ones such us Viscosity, Thermal conductivity, Velocity, Elevation, thermal expansion coefficient… In thermodynamics and materials science, the physical properties of substances are often described as intensive or extensive, a classification that relates to the dependency of the properties upon the size or extent of the system or object in question. Thermodynamic concept Thermodynamic & Energy Property of the system: The distinction is based on the concept that smaller, non-interacting identical subdivisions of the system may be identified so that the property of interest does or does not change when the system is divided, or combined. An intensive property is a bulk property, meaning that it is a physical property of a system that does not depend on the system size or the amount of material in the system. Examples of intensive properties are the temperature and the hardness of an object. No matter how small a diamond is cut, it maintains its intrinsic hardness. Thermodynamic concept Thermodynamic & Energy Property of the system: By contrast, an extensive property is one that is additive for independent, noninteracting subsystems. The property is proportional to the amount of material in the system. For example, both the mass and the volume of a diamond are directly proportional to the amount that is left after cutting it from the raw mineral. Mass and volume are extensive properties, but hardness is intensive. The ratio of two extensive properties, such as mass and volume, is scaleinvariant, and this ratio, the density, Thermodynamic concept Thermodynamic & Energy Corresponding extensive and intensive thermodynamic properties Extensive property Symbol SI units Intensive property Symbol SI units Volume V m3 or L* Specific volume*** V m3/kg or L*/kg Internal energy U J Specific internal energy u J/kg Entropy S J/K Specific entropy S J/(kg·K) Enthalpy H J Specific enthalpy h J/kg Gibbs free energy G J Specific Gibbs free energy g J/kg Thermodynamic concept Thermodynamic & Energy Corresponding extensive and intensive thermodynamic properties Extensive property Heat capacity at constant volume Heat capacity at constant pressure Symbol Cv Cp SI units J/K J/K Intensive property Specific heat capacity at constant volume Specific heat capacity at constant pressure *L = liter, J = joule **Specific properties, expressed on a per mass basis ***Specific volume is the reciprocal of density. Symbol SI units Cv J/(kg·K) Cp J/(kg·K) Thermodynamic concept Thermodynamic & Energy State of equilibrium: Equilibrium implies a state of balance. A system which is in equilibrium experiences NO changes when it is isolated from its surrounding. Kind of Equilibrium: 1. Thermal equilibrium. 2. Mechanical equilibrium. 3. Phase equilibrium. 4. Chemical equilibrium. Thermodynamic concept Thermodynamic & Energy State of equilibrium: In non-equilibrium systems there are net flows of matter or energy, or phase changes are occurring; if such changes can be triggered to occur in a system in which they are not already occurring, it is said to be in a metastable equilibrium. When a body of material starts from a non-equilibrium state of inhomogeneity or chemical non-equilibrium, and is then isolated, it spontaneously evolves towards its own internal state of thermodynamic equilibrium. It is not necessary that all aspects of internal thermodynamic equilibrium be reached simultaneously; some can be established before others. Thermodynamic concept Thermodynamic & Energy Fig: show the characteristics of equilibrium state. Thermodynamic concept Thermodynamic & Energy Equilibrium: A System is in Equilibrium if its Properties/Variables do not change with time. Thermal Equilibrium No Temperature or Pressure Gradients in the System. Mechanical Equilibrium No Unbalanced Forces or Torques in the System. Chemical Equilibrium No tendency of the System to undergo Chemical Reaction or Diffusion. Electrical Equilibrium No Electrical Potential Gradients in the System Thermodynamic concept Thermodynamic & Energy Thermal Processes: When a substance changes from on state of equilibrium to another state of equilibrium, the steps or path between the initial and final thermodynamic states is call the process. Thermodynamic concept Thermodynamic & Energy Quasi-Equilibrium Processes: A process is call a quasi-equilibrium process if the intermediate steps in the process are all close to equilibrium. I this way we can characterize the intermediate states of the process using state variables (such as temperature, pressure, volume, entropy, etc. See important thermal processes. When a process is quasi-equilibrium we can plot the path of the process on say a pressure vs. Say volume work diagram since all the variable used to characterize the substance's intermediate states have well define values. Thermodynamic concept Thermodynamic & Energy Quasi-Equilibrium Processes: Most of the process you will encounter will be quasi-equilibrium process and we will drop the "quasi-equilibrium" when talking about a particular process. Path: series of states through which a system passes during a process. Thermodynamic concept Thermodynamic & Energy State Variable: Examples of State Variables: 1. Temperature 2. Pressure Volume 3. Entropy 4. Enthalpy 5. Internal 6. Energy 7. Mass Density State Variables are Path Independent: Meaning that the change in the value of the state variable will be the same no matter what path you take between the two states. This is not true of either the work W or the heat Q. Thermodynamic concept Thermodynamic & Energy State Variable: If a system is carried through a cycle that returns it to its original state, then a variable will only be a state variable if variable returns to its original value. If X is a State Variable then: ‫=𝑥𝑑 ׬‬0 State Variables are only measurable when the system is in Equilibrium. Thermodynamic concept Thermodynamic & Energy Reversible Processes: In thermodynamics, a reversible process, or reversible cycle if the process is cyclic, is a process that can be "reversed" by means of infinitesimal changes in some property of the system without entropy production (i.e. dissipation of energy) Due to these infinitesimal changes, the system is in thermodynamic equilibrium throughout the entire process. Since it would take an infinite amount of time for the reversible process to finish, perfectly reversible processes are impossible. However, if the system undergoing the changes responds much faster than the applied change, the deviation from reversibility may be negligible. Thermodynamic concept Thermodynamic & Energy Reversible Processes: In a reversible cycle, the system and its surroundings will be exactly the same after each cycle. An alternative definition of a reversible process is a process that, after it has taken place, can be reversed and causes no change in either the system or its surroundings. In thermodynamic terms, a process "taking place" would refer to its transition from its initial state to its final state. Thermodynamic concept Thermodynamic & Energy Irreversible Processes: All Natural processes are Irreversible. The path of an irreversible process is indeterminate and cannot be drawn on a thermodynamic diagram. We use a hashed line to indicate the path because the intermediate states are in non-equilibrium. The Entropy of the universe always increases during an irreversible process. It is always possible to restore an irreversible process to its original state by a reversible process, but the Entropy of the universe can never be restored. Thermodynamic concept Thermodynamic & Energy Irreversible Processes: An irreversible process always requires an external agent to restore it to its original state. Examples of Irreversible Processes: Friction Heat Flow Unrestrained Expansion Melting/Boiling Mixing Unrestrained Expansion Chemical Reactions Mixing Your House Getting Dirty Thermodynamic concept Thermodynamic & Energy A process-data diagram: Is a diagram that describes processes and data that act as output of these processes. Process diagrams which are plotted by employing thermodynamic properties as coordinate are very useful in visualizing the process. Some common properties that are used as coordinate are (T, P, V or specific volume v ). A pressure volume diagram (or PV diagram, or volume-pressure loop) is used to describe corresponding changes in volume and pressure in a system. Thermodynamic concept Thermodynamic & Energy A process-data diagram: They are commonly used in thermodynamics, cardiovascular physiology, and respiratory physiology. Fig: show the P-V diagram. Thermodynamic concept Thermodynamic & Energy A process-data diagram: Fig : show pressure and specific volume diagram Thermodynamic concept Applications Thermodynamics PV diagrams can be used to estimate the net work performed by a thermodynamic cycle. The network is the area enclosed by the PV curve in the diagram. This usage derived from the development of indicator diagrams which were used to estimate the performance of a steam engine. Specifically, the diagram records the pressure of steam versus the volume of steam in a cylinder, throughout a piston's cycle of motion in a steam engine. The diagram enables calculation of the work performed and thus can provide a measure of the power produced by the engine. Thermodynamic concept Applications Thermodynamics Thermodynamic concept Applications Thermodynamics To exactly calculate the work done by the system it is necessary to calculate the integral of the pressure with respect to volume. One can often quickly calculate this using the PV diagram as it is simply the area enclosed by the cycle. Note: That in some cases specific volume will be plotted on the x-axis instead of volume, in which case the area under the curve represents work per unit mass of the working fluid (i.e. J/kg) Thermodynamic concept Applications Medicine In cardiovascular physiology, the diagram is often applied to the left ventricle, and it can be mapped to specific events of the cardiac cycle. PV loop studies are widely used in basic research and preclinical testing, to characterize the intact heart's performance under various situations (effect of drugs, disease, characterization of mouse strains), The sequence of events occurring in every heart cycle is as follows. The left figure shows a PV loop from a real experiment; letters refer to points. Thermodynamic concept Applications Medicine Thermodynamic concept Applications Medicine Human heart Thermodynamic concept Human heart A is the end-diastolic point; this is the point where contraction begins. Pressure starts to increase, becomes rapidly higher than the atrial pressure, and the mitral valve closes. Since pressure is also lower than the aortic pressure, the aortic valve is closed as well. Segment AB is the contraction phase. Since both the mitral and aortic valves are closed, volume is constant. For this reason, this phase is called isovolumic contraction. Thermodynamic concept Human heart At point B, pressure becomes higher than the aortic pressure and the aortic valve opens, initiating ejection. BC is the ejection phase, volume decreases. At the end of this phase, pressure lowers again and falls below aortic pressure. The aortic valve closes. Point C is the end-systolic point. Segment CD is the isovolumic relaxation. Thermodynamic concept Human heart During this phase, pressure continues to fall. The mitral valve and aortic valve are both closed again so volume is constant. At point D pressure falls below the atrial pressure and the mitral valve opens, initiating ventricular filling. DA is the diastolic filling period. Blood flows from the left atrium to the left ventricle. Atrial contraction completes ventricular filling. Thermodynamic concept Human heart As it can be seen, the PV loop forms a roughly rectangular shape and each loop is formed in an anti-clockwise direction. Very useful information can be derived by examination and analysis of individual loops or series of loops, for example: 1. The horizontal distance between the top-left corner and the bottom-right corner of each loop is the stroke volume 2. The line joining the top-left corner of several loops is the contractile or inotropic state. Thermodynamic concept Isothermal process An isothermal process is a change of a system, in which the temperature remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir (heat bath), and the change occurs slowly enough to allow the system to continually adjust to the temperature of the reservoir through heat exchange. In contrast, an adiabatic process is where a system exchanges no heat with its surroundings (Q = 0). In other words, in an isothermal process, the value ΔT = 0 but Q ≠ 0, while in an adiabatic process, ΔT ≠ 0 but Q = 0. Thermodynamic concept Applications Medicine Thermodynamic concept Isobaric process: An isobaric process is a thermodynamic process in which the pressure remains constant. This is usually obtained by allowed the volume to expand or contract in such a way to neutralize any pressure changes that would be caused by heat transfer. Thermodynamic concept Isochoric process: An isochoric process, also called a constant-volume process, an iso volumetric process, or an isometric process, is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant. Isochoric process is exemplified by the heating or the cooling of the contents of a sealed, inelastic container: The thermodynamic process is the addition or removal of heat; The isolation of the contents of the container establishes the closed system; And the inability of the container to deform imposes the constant-volume Thermodynamic concept Applications Medicine Thermodynamic concept Isochoric process: Fig :isothermal, isobaric and isochoric process Thermodynamic concept Adiabatic process: An adiabatic process is a process that occurs without the transfer of heat or matter between a system and its surroundings. Adiabatic transfer provides a rigorous conceptual basis for the theory used to expound the first law of thermodynamics. It is also key in a practical sense, that many rapid chemical and physical processes are described using the adiabatic approximation; such processes are usually followed or preceded by events that do involve heat transfer. Adiabatic processes are primarily and exactly defined for a system contained by walls that are completely thermally insulating and impermeable to matter; such walls are said to be adiabatic. Thermodynamic concept Adiabatic process: An adiabatic transfer is a transfer of energy as work across an adiabatic wall or sector of a boundary. Thermodynamic concept Adiabatic process: Thermodynamic concept Adiabatic process: