ENGN 401 - Thermo

ENGN 401 - Thermo - ENGN 401 Thermodynamics Review October...

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ENGN 401 Thermodynamics Review October 8, 2010
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Introduction Definitions and Fundamental Ideas Thermodynamics Continuum Model Concept of System Concept of State Concept of Equilibrium Concept of Process Equations of State
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Thermodynamics Thermodynamics can be defined as the science of energy. Energy can be considered as the ability to cause changes (e.g. changes in temperature, transformation of energy, and the relationships between heat and work). It is used to describe the performance of propulsion systems, power generation systems, refrigerators, in addition to several cases of fluid flow and combustion.
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Thermodynamics The focus of thermodynamics is often on the production of work, often in the form of kinetic energy (for example in the exhaust of a jet engine) or shaft power, from different sources of heat Propulsion System: Converting heat to useful work Refrigerator: Converting work to useful heat
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Continuum Model Matter may be described at a molecular (or microscopic) or macroscopic level (averaged) A microscopic description of an engineering device may produce too much information to manage For example, 1 mm 3 of air at standard temperature and pressure contains 10 16 molecules, each of which has a position and a velocity
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Continuum Model Microscopic positions and velocities are generally not useful for determining how macroscopic systems will act or react. We therefore neglect the fact that real substances are composed of discrete molecules and model matter as a continuum – an infinitely divisible medium with microscopic data averaged over a volume
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Concept of a System A thermodynamic system is a quantity of matter of fixed identity, around which we can draw a boundary The boundaries may be fixed or moving
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Concept of System Work or heat can be transferred across the system boundary. Everything outside the boundary is the surroundings . When working with devices such as engines, it is often useful to define the system to be an identifiable volume with flow in and out. This is termed a control volume .
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Concept of System (Control Volume)
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Concept of State The thermodynamic state of a system is defined by specifying values of a set of measurable properties sufficient to determine all other properties For fluid systems, typical properties are pressure, volume and temperature.
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Concept of State Properties may be extensive or intensive Extensive properties are additive If the system is divided into a number of sub- systems, the value of the property for the whole system is equal to the sum of the values for the parts Intensive properties do not depend on the quantity of matter present Temperature and pressure are intensive properties
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Specific properties are extensive properties per unit mass and are denoted by lower case letters. For example:
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This note was uploaded on 10/26/2010 for the course ME 401 taught by Professor Hao during the Spring '10 term at Old Dominion.

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ENGN 401 - Thermo - ENGN 401 Thermodynamics Review October...

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