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Systems and Control VolumeA Open system (also known as a control
volume) is one in which both mass and energy cross the boundary.
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PROPERTIES OF A SYSTEMAny characteristic of a system is called a
property.Intensive properties are those that are
independent of the mass of a system.Extensive properties are those whose values
depend on the size or extent of the system such as proportional to mass of system.
Extensive properties per unit mass are called specific properties.
A continuous, homogeneous matter with no holes, that is, a continuum.
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The mass of the whole is the sum of the masses of the parts, and the overall volume is the sum of the volumes of the parts. However, the temperature of the whole is not the sum of the temperatures of the parts; it is the same for each part. Mass and volume are extensive, but temperature is intensive.
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Density and specific gravityDensity is defined as mass per unit volume.The reciprocal of density is the specific
volume v, which is defined as volume per unit mass.
Specific gravity or relative density is ratio of the density of a substance to the density of some standard substance at a specified temperature.
The weight of a unit volume of a substance is called specific weight.
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State and EquilibriumEach unique condition of system is called
state.In an equilibrium state there are no
unbalanced potentials (or driving forces) within the system.
The system will be in thermal equilibrium if its temperature is same throughout the system.
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Figure1: A closed system reaching thermal equilibrium
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State and EquilibriumMechanical equilibrium is related to
pressure, and a system is in mechanical equilibrium if there is no change in pressure at any point of the system with time.
If a system involves two phases, it is in phase equilibrium when the mass of each phase reaches an equilibrium level and stays there.
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State and EquilibriumA system is in chemical equilibrium if its
chemicalcomposition does not change with time,
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QUIZDistinguish between intensive and extensive
properties.Mass, Volume ,Energy,
Momentum,Temperature,Pressure,Density
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State PostulateThe number of properties required to fix the
state of a system is given by the state postulate.
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Process and CycleAny change that a system undergoes from
one equilibrium state to another is called a process, and the series of states through which a system passes during a process is called the path of the process.
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Process and CycleWhen a process proceeds in such a manner
that the system remains infinitesimally close to an equilibrium state at all times, it is called a quasi- static, or quasi-equilibrium, process. A quasi-equilibrium process can be viewed as a sufficiently slow process that allows the system to adjust itself internally so that properties in one part of the system do not change any faster than those at other parts.
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Process and Cycle
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Process and Cycle
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Process and CycleThe prefix iso- is often used to designate a
process for which a particular property remains constant.
Isothermal process During an isothermal process there are no
temperature changes, i.e., dT = 0. Isobaric process For an isobaric process the pressure is constant (dP
= 0). Isometric or Isochoric process In isometric process the specific volume remains
unchanged (dv = 0).May 1, 2023 19
Process and CycleAdiabatic process In adiabatic process there is no heat transfer, i.e.,
when the system is perfectly insulated.
The terms steady and uniform are used frequently in engineering
The term steady implies no change with time. The opposite of steady is unsteady, or transient. The term uniform, however, implies no change with location over a specified region.
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Process and Cycle
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TEMPERATURE AND THE ZEROTH LAW OF THERMODYNAMICSAlthough we are familiar with temperature as
a measure of “hotness” or “coldness,” it is not easy to give an exact definition for it. Based on our physiological sensations, we express the level of temperature qualitatively with words like freezing cold, cold, warm, hot, and red-hot.
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TEMPERATURE AND THE ZEROTH LAW OF THERMODYNAMICS
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TEMPERATURE AND THE ZEROTH LAW OF THERMODYNAMICSThe zeroth law of thermodynamics states
that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.
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Temperature Scales
Temperature scales enable us to use a common basis for temperature measurements.
The Kelvin scale is related to the Celsius scale by
The Rankine scale is related to the Fahrenheit scale by
The temperature scales in the two unit systems are related by
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Temperature Scales
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