Anh Văn CN Nhiệt chapter 3

Anh văn Chuyên ngành Nhiệt English for thermal engineering LOGO Chapter The laws of thermodynamics Contents The first law of thermodynamics The second law of thermodynamics The thermodynamic cycles Tài liệu tham khảo Fundamentals of thermal-fluid science, Y A Çengel Fundamentals of thermodynamics (sixth edition), Sonntag, Borgnakke and van Wylen Fundamentals of engineering thermodynamics (Fifth edition), Michael J Moran, Howard N Shapiro Chapter The laws of thermodynamics The first law The first law of thermodynamics is essentially an expression of the conservation of energy principle, also called the energy balance Statements The first law of thermodynamics states that energy can be neither created nor destroyed; it can only change forms The change in internal energy of a system is equal to the heat added to the system minus the work done by the system Chapter The laws of thermodynamics The first law For closed system or The energy balance in differential form: The instantaneous time rate form of the energy balance: Chapter The laws of thermodynamics The first law For closed system Stationary systems: Per unit mass: The energy change of a system during a process is equal to the net work and heat transfer between the system and its surroundings Figure Chapter The laws of thermodynamics The first law Example 1: Heating of a Gas by a Resistance Heater A piston-cylinder device initially contains 0.5 m3 of nitrogen gas at 400 kPa and 27°C An electric heater within the device is turned on and is allowed to pass a current of A for from a 120-V source Nitrogen expands at constant pressure, and a heat loss of 2800 J occurs during the process Determine the final temperature of nitrogen Assumptions: Nitrogen is an ideal gas KE = PE = and E = U The pressure is constant Specific heat is constant Figure Chapter The laws of thermodynamics The second law Kelvin-Planck Statement: “It is impossible for any system to operate in a thermodynamic cycle and deliver a net amount of energy by work to its surroundings while receiving energy by heat transfer from a single thermal reservoir In other words, a perpetual motion machine of the second kind is impossible” Heat is transferred to a heat engine from a furnace at a rate of 80 MW And the rate of waste heat rejection to a nearby river is 50 MW Figure Chapter The laws of thermodynamics The second law The Clausius statement “It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher- temperature body.” A refrigerator that violates the Clausius statement of the second law Figure Chapter The laws of thermodynamics Thermodynamic cycles Power cycle Systems undergoing cycles of the type shown in Fig deliver a net work transfer of energy to their surroundings during each cycle The thermal efficiency: Figure 5: Schematic diagrams of power cycles Chapter The laws of thermodynamics Thermodynamic cycles Refrigeration and Heat Pump Cycles The refrigeration and heat pump cycles shown in Fig Figure 6: Schematic diagrams of Refrigeration and heat pump cycles Chapter The laws of thermodynamics Thermodynamic cycles Refrigeration Cycle The performance of refrigeration cycles can be described by the coefficient of performance, COP, is: Heat pump Cycle Figure 6: Schematic diagrams of Refrigeration and heat pump cycles LOGO ... by the system Chapter The laws of thermodynamics The first law For closed system or The energy balance in differential form: The instantaneous time rate form of the energy balance: Chapter The... its surroundings Figure Chapter The laws of thermodynamics The first law Example 1: Heating of a Gas by a Resistance Heater A piston-cylinder device initially contains 0.5 m3 of nitrogen gas at.. .Chapter The laws of thermodynamics Contents The first law of thermodynamics The second law of thermodynamics