Termodinamica

 Independent of the size or extent of a system. Examples: pressure,temperature.

Its value is not additive as for extensive properties.

May vary from place to place within the system at any moment – function of both position and time.

10

 When a system is isolated, it does not interact with its surroundings; however, its state can change as a consequence of spontaneous events occurring internally as its intensive properties such as temperature and pressure tend toward uniform values. When all such changes cease, the system is at an equilibrium state.

 Equilibrium states and processes from one equilibrium state to another equilibrium state play important roles in thermodynamic analysis.

11



Energy is an extensive property that includes the kinetic and gravitational potential energy of engineering mechanics.

 For closed systems, energy is transferred in and out across the system boundary by two means only: by work and by heat.

Energy is conserved. This is the first law of thermodynamics.

13

The closed system energy balance states:

The change in the amount of energy contained within a closed system during some time interval

Net amount of energy transferred in and out across the system boundary by heat and work during the time interval

We now consider several aspects of the energy balance, including what is meant by energy change and energy transfer.

14

 In engineering thermodynamics the change in energy of a system is composed of three contributions:

 Kinetic energy

 Gravitational potential energy  Internal energy

15

 The change in kinetic energy is associated with the motion of the system as a whole relative to an external coordinate frame such as the surface of the earth.

For a system of mass m the change in kinetic energy from state 1 to state 2 is

∆KE=KE –KE =1m(V2−V2) 21221

where

►V1 and V2 denote the initial and final velocity magnitudes. ►The symbol ∆ denotes: final value minus initial value.

(Eq. 2.5)

16

►The change in gravitational potential energy is associated with the position of the system in the earth’s gravitational field.

►For a system of mass m the change in potential energy from state 1 to state 2 is

where

∆PE=PE2 –PE1 =mg(z2 –z1)

(Eq. 2.10)

 z1 and z2 denote the initial

...