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1. Fundamental Concepts and    Definitions

                        1.1 Thermodynamic system
                  When analyzing physical  situations we usually focus our attention on some portion
            of matter which we  separate, in our minds, from the environment external to it.  We
            call  such    a  portion  the  system.    Everything  outside  the    system  which  has  a  direct
            bearing  on  its  behavior  is  called  the  environment.  Then  we  seek  to  determine  the
            behavior  of the system by finding  how  it interacts with its environment.
                  Thermodynamic system is called some portion of  matter  which can interact  with its
            environment by the energy exchange i.e. performance of some work or transfer of some
            heat (fig. 1.1).
                  The  quantity of  matter or region of space  must be within a prescribed boundary.
            This boundary may be deformable and may be imaginary.
                  Everything outside the system boundary is referred to as the surroundings. Usually
            the term surroundings is restricted to those things outside the system that in some way
            interact with the system or affect the behavior of the system.
            The system can be divided to three types, which are:
               - A Closed System
              - An Isolated System
              - An Open System)
                  If a system  is defined as a particular quantity of matter, then the system always
            contains  the  same  matter  and  there  can  be  no  transfer  of  mass  across  the  boundary.
            However, if a system is defined as a region of space within a prescribed boundary, then
            matter may cross the system boundary. In order to distinguish between these two types
            of  systems,  the  type  that  has  no  mass  transfer  across  its  boundary  we  call  a  closed
            system or control mass. An open system is a region of space within a boundary which
            matter  may  cross.  This  boundary  may  be  moving.  An  open  system  is  also  called  a
            control volume and its boundary is called a control surface.
                  A  special  case  of  a  closed  system  is  an  isolated  system.  An  isolated  system  is  a
            system that  in  no way  interacts with  its surroundings. Notice that an  isolated system
            must be a closed system, since the requirement that there be no interaction of the system
            with its surroundings prohibits any transfer of mass across the system boundary.
                                                    Examples of systems used in thermodynamic analysis
                                              range  from  tiny  partials  to  complete,  complex  power
                                              plants and even to large regions in the earth's atmosphere.
                                                    The most important step in the solution of a problem
                                              in  thermodynamics  is  often  the  selection  and  careful
                                              specification of the system which is to be considered. The
                                              importance of this step will be emphasized frequently later
                                              in  this  synopsis.  A  example  of    thermodynamic  systems
                                              will now be considered.
                                                    Examples of systems used in thermodynamic analysis
                                               range  from  tiny  partials  to  complete,  complex  power
             Fig.1.1-thermodynamic  system    plants and even to large regions in the earth's atmosphere.


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