Basic Mine Thermodynamics-ER 1050 L2-System and its Surroundings (PDF)

Basic Mine Thermodynamics-ER 1050 E n g. ( M rs. ) B. D. N a d e e ra M a d h u b h a s h a n i B a ta p o l a D e p a r t m e nt o f Ea r t h Re s o u r c e s E n g i n e e r i n g U n i v e rs i t y o f M o ra t u wa System and its Surroundings 2 System and its Surr...

Basic Mine Thermodynamics-ER 1050 E n g. ( M rs. ) B. D. N a d e e ra M a d h u b h a s h a n i B a ta p o l a D e p a r t m e nt o f Ea r t h Re s o u r c e s E n g i n e e r i n g U n i v e rs i t y o f M o ra t u wa System and its Surroundings 2 System and its Surroundings  System A system is defined as a quantity of matter or a region in space chosen for a particular study.  Surroundings The mass or region outside the system is called the surroundings.  Boundary The real or imaginary surface that separates the system from its surroundings. Can be fixed or movable, and has no thickness. Source: https://mechtics.com/energy/system-and- surroundings-in-thermodynamics/ 3 Systems Systems can be either closed or open, depending whether they have a fixed mass or fixed volume.  Closed Systems Also known as a control mass Consists of a fixed amount of mass, thus no mass can cross the boundary of system. But energy, in the form of heat or work, can cross the boundary; and the volume of a closed system does not have to be fixed. Source: https://psiberg.com/open-closed-and-isolated- systems-with-examples/ 4  Systems  Closed Systems No Mass Transfer Source: https://energyeducation.ca/encyclopedia/System_and_surrounding Source: https://gyan4all.com/thermodynamic-system- definition-types-and-examples/ 5 Systems  Open Systems In an open system (or a control volume), both mass and energy can cross the boundary. It usually encloses a device that involves mass flow such as a compressor, turbine, or nozzle. A large number of engineering problems involve mass flow in and out of a system and, therefore, are modeled as control volumes, not as control masses. Source: https://psiberg.com/open-closed-and-isolated- systems-with-examples/ 6 Systems  Open Systems In general, any arbitrary region in space can be selected as a control volume. But the proper choice certainly makes the analysis much easier. Example: If we were to analyze the flow of air through a nozzle, a good choice for the control volume would be the region within the nozzle. Source: https://studiousguy.com/open-system-examples/ 7 Systems  Open Systems Source: https://www.sciencedirect.com/topics/engineering/thermodynamic-system The boundaries of a control volume are called a control surface, and they can be real or imaginary. Real boundary The boundaries of a control volume are called a control surface, and they can be real or imaginary. A control volume can be fixed in size and shape, as in a nozzle. Or it may involve a moving boundary. Imaginary boundary Source: https://studiousguy.com/open-system-examples/ 8 Systems  Open Systems Source: https://gyan4all.com/thermodynamic- system-definition-types-and-examples/ Source: Yıldız et al. (2021) Source: https://energyeducation.ca/encyclopedia/System_and_surrounding 9 Systems  Isolated Systems A special case of a closed system The system in which neither energy nor matter can be exchanged with surroundings is called an isolated system. An isolated system may be a portion of larger systems, but they do not communicate with outside in any way. Source: https://psiberg.com/open-closed-and-isolated- systems-with-examples/ 10 Systems  Isolated Systems Source: https://energyeducation.ca/encyclopedia/Sys tem_and_surrounding Source: https://www.mechstudies.com/open-system-closed-system-isolated-system/ Source: https://www.slideserve.com/harper/thermochemistry 11 Properties of a System Any characteristic of a system is called a property. Some familiar properties are: Pressure (P), Temperature (T), Volume (V), Mass (m) Also, there are viscosity, thermal conductivity, modulus of elasticity, electrical resistivity, etc. Properties can be divided into: intensive and extensive Intensive properties – Independent of the mass of a system (E.g: Temperature, Pressure, Density) Extensive properties – Depend on the size or the extent of a system (E.g: Total mass, Total volume, Total momentum) Extensive properties per unit mass – specific properties [E.g: specific volume (V/m), specific total energy (E/m)] 12 Properties of a System m V T P ? ρ 13 What is Continuum? Concept of continuum – The assumption of a continuous, homogeneous matter with no voids It allows us to treat properties as point functions and to assume the properties vary continually in space with no jump discontinuities. However, this idealisation is valid as long as the size of the system we deal with is large relative to the space between the molecules. 14 State and Equilibrium The state is a set of properties that completely describes the condition of a system, which does not undergo any change. At a given state, all the properties of a system have fixed values. If the value of even one property changes, the state will change to a different one. State 2 State 1 m = 2 kg m = 2 kg T2 = 20 °C T1 = 20 °C V2 = 2.5 m3 V1 = 1.5 m3 15 State and Equilibrium If a system experiences no changes when it is isolated from the surroundings, it is in an equilibrium state. In equilibrium state, there are no unbalanced potentials (or driving forces) within the system. There are many types of equilibrium states. Examples: Thermal Equilibrium Mechanical Equilibrium Phase Equilibrium Chemical Equilibrium 16 The State Postulate The state of a simple compressible system is completely specified by two independent, intensive properties. A simple compressible system has no electrical, magnetic, gravitational, motion, and surface tension effects. For example, temperature and specific volume can fix the state of a simple compressible system. However, temperature and pressure are independent properties for single- phase systems, but are dependent properties for multiphase systems. 17 The State Postulate Nitrogen T = 25 °C v = 0.9 m3/kg Source: https://socratic.org/questions/how-do-boiling-points-change-at-high-altitudes The state of nitrogen is fixed T = f(P ) during a phase-change process; thus, by two independent intensive temperature and pressure are not sufficient to properties fix the state of a two-phase system. 18 Processes and Cycles  Process Any change that a system undergoes from one equilibrium state to another. The series of states through which a system passes during a process is called the path of the process. Source: https://sbainvent.com/thermodynamics/processes-and-cycles/ 19 Processes and Cycles  Process There are six types of processes associated with thermodynamics.  Adiabatic – No heat transfer between the system and surroundings  Isothermal – No change in system’s temperature  Isobaric – No change in system’s pressure  Isochoric – No change in system’s volume Source:  Isentropic – No change in system’s entropy https://medium.com/@sanskruti.patil21/types- of-thermodynamic-processes-and-their-  Isenthalpic – No change in system’s enthalpy significance-507864edcf82 20 Processes and Cycles  Process Diagrams Useful in visualizing processes, where they are plotted as coordinates of thermodynamic properties. Some common properties that are used as coordinates are temperature (T), pressure (P), and volume (V). Source: Cengel and Boles (2008) 21 Processes and Cycles  Cycles 1 Collection of processes where initial and final states are identical. 1 and 2 are states 2 1-2 (Path A) and 2-1 (Path B) are processes 1-A-2-B-1 is a cycle. Source: http://www.mecha- engineeringbd.com/2016/06/thermodynamic-process- cycle.html#google_vignette 22 The Steady-Flow Process A process during which a fluid flows through a control volume steadily. That means the fluid properties can change from point to point within the control volume, but at any fixed point they remain the same during the entire process. Therefore, the volume (V), the mass (m), and the total energy content (E) of the control volume remain constant during a steady-flow process. Source: https://sbainvent.com/thermodynamics/steady- flow-process/ 23 The Steady-Flow Process Steady-flow conditions can be closely approximated by devices that are intended for continuous operation such as turbines, pumps, boilers, condensers, and heat exchangers or power plants or refrigeration systems. Some cyclic devices, such as reciprocating engines or compressors, do not satisfy any of the conditions stated above since the flow at the inlets and the exits will be pulsating and not steady. However, the fluid properties vary with time in a periodic manner, and the flow through these devices can still be analyzed as a steady-flow process by using time-averaged values for the properties. 24 Modes of Energy Transfer  Heat Form of energy that is transformed between two systems (or system and surrounding due to temperature difference).  Work Energy interaction between system and surroundings other than the heat. 25 Modes of Energy Transfer  Similarities between work and heat Can be recognized only when they cross the boundary (boundary Phenomena) System posses energy neither heat nor work (transient phenomena) Both are associated with process not with state Both are path functions depend on the path followed in the process 26 Modes of Energy Transfer  Conduction  Convection  Radiation Source: https://www.linkedin.com/pulse/heat-transfer-modes-boiler-muhammed-zakiy-k/ 27 THANK YOU!