HYDRO ELECTRIC POWER PLANT

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HYDRO ELECTRIC POWER PLANT

• AGUS HARYANTO

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OBJECTIVES

• Introduce concept of energy and its various
  forms.
• Discuss the nature of internal energy.
• Define concept of heat and terminology associated
• Define concept of work and forms of mechanical
  work.
• Define energy conversion efficiencies.
• Discuss relation of energy conversion and
  environment.

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Recall ENERGY SISTEM TERMODINAMIKA

• BENTUK ENERGI
• 1. Energi Kinetik (KE) ?
• 2. Energi Potensial (PE) ? PE mgh
• 3. Energi dakhil atau Internal Energy (U)
• ENERGI TOTAL
• E U KE PE
• e u ke pe (per satuan massa)

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Thermodynamics Concern

• Thermodynamics deals only with the change of the
  total energy (?E). Thus E of a system can be
  assigned to zero (E 0) at some reference point.
  
• The change in total energy (?E) of a system is
  independent of the reference point selected.
• For stationary systems, the ?E is identical to
  the change of internal energy ?U.

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Macroscopic vs. Microscopic Energy

• The macroscopic forms of energy are those a
  system possesses as a whole with respect to some
  outside reference frame, such as kinetic and
  potential energies.
• The microscopic forms of energy are those related
  to the molecular structure of a system and the
  degree of the molecular activity, and they are
  independent of outside reference frames. The sum
  of all the microscopic forms of energy is called
  the internal energy of a system and is denoted by
  U.

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More on Internal Energy
SENSIBLE and LATENT energy

• The internal energy of a system is the sum of
  all forms of the microscopic energies.

CHEMICAL energy
NUCLEAR energy
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More on Internal Energy Sensible Energy

• The portion of the internal energy of a system
  associated with the kinetic energies of the
  molecules is called the sensible energy

The various forms of microscopic energies that
make up sensible energy
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More on Internal Energy Latent Energy

• The internal energy associated with the phase of
  a system is called the latent energy.
• The amount of energy absorbed or released during
  a phase-change process is called the latent heat
  coefficient.
• At 1 atm, the latent heat coefficient of water
  vaporization is 2256.5 kJ/kg.

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More on Internal Energy Chemical and Nuclear
Energy

• The internal energy associated with the atomic
  bonds in a molecule is called chemical energy.
• The tremendous amount of energy associated with
  the strong bonds within the nucleus of the atom
  itself is called nuclear energy.

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Energy Transfer Heat vs. Works

• Energy crosses the boundaries in the form of
• Heat
• Work
• Mass flow

) 1,2 for Clossed System 1,2,3 for Open System
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HEAT (Q)

• Heat the form of energy that is transferred
  between two systems (or a system and its
  surroundings) by virtue of a temperature
  difference

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WORK (W)

• Mechanics work is the energy transfer associated
  with a force acting through a distance (W F.s).
• Thermodynamics work is an energy interaction
  that is not caused by a temperature difference
  between a system and its surroundings.

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Sign Convention

-
-

• Qin (positive)
• Qout - (negative)
• Win - (negative)
• Wout (positive)

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Note on HEAT and WORK

1. Both are recognized at the boundaries of a system
   as they cross the boundaries. That is, both heat
   and work are boundary phenomena.
2. Systems possess energy, but not heat or work.
3. Both are associated with a process, not a state.
   Unlike properties, heat or work has no meaning at
   a state.
4. Both are path functions (i.e., their magnitudes
   depend on the path followed during a process as
   well as the end states), and not point functions.

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Path vs. Point Functions

• Path functions have inexact differentials
  designated by ?(?Q or ?W) NOT dQ or dW.
• Properties are point functions (i.e., they depend
  on the state only, and not on how a system
  reaches that state), and they have exact
  differentials designated by d. A small change in
  volume, for example, is represented by dV.

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Path vs. Point Functions

• Properties are point functions
• Heat and Work are path functions

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Example1

• A candle is burning in a well-insulated room.
  Taking the room (the air plus the candle) as the
  system, determine (a) if there is any heat
  transfer during this burning process and (b) if
  there is any change in the internal energy of the
  system.

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Example1 Solution

• (a) The interior surfaces of the room form the
  system boundary. As pointed out earlier, heat is
  recognized as it crosses the boundaries. Since
  the room is well insulated, we have an adiabatic
  system and no heat will pass through the
  boundaries. Therefore, Q 0 for this process.
• (b) The internal energy involves energies that
  exist in various forms. During the process just
  described, part of the chemical energy is
  converted to sensible energy. Since there is no
  increase or decrease in the total internal energy
  of the system, ?U 0 for this process.

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Example2

• A potato initially at room temperature (25C) is
  being baked in an oven that is maintained at
  200C, as shown in Fig. 221. Is there any heat
  transfer during this baking process?

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Example2 Solution

• This is not a well-defined problem since the
  system is not specified. Let us assume that we
  are observing the potato, which will be our
  system. Then the skin of the potato can be viewed
  as the system boundary. Part of the energy in the
  oven will pass through the skin to the potato.
  Since the driving force for this energy transfer
  is a temperature difference, this is a heat
  transfer process.
• Note if the system is the oven, then Q 0

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Example2

• A well-insulated electric oven is being heated
  through its heating element. If the entire oven,
  including the heating element, is taken to be the
  system, determine whether this is a heat or work
  interaction.
• How if the system is taken as only the air in the
  oven without the heating element.

Electrical Work Wel V.I.t I.R.I.t
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Example3 Solution 1st Case

• The energy content of the oven obviously
  increases during this process, as evidenced by a
  rise in temperature. This energy transfer to the
  oven is not caused by a temperature difference
  between the oven and the surrounding air.
  Instead, it is caused by electrons crossing the
  system boundary and thus doing work. Therefore,
  this is a work interaction.

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Example3 Solution 2nd Case

• This time, no electrons will be crossing the
  system boundary at any point. Instead, the energy
  generated in the interior of the heating element
  will be transferred to the air around it as a
  result of the temperature difference between the
  heating element and the air in the oven.
  Therefore, this is a heat transfer process.

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MECHANICAL FORMS OF WORK

• Kinetical Work
• Wk F.s
• Wb P.A.ds P.dV

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Example

• Sebuah tangki kokoh berisi udara pada 500 kPa dan
  150oC. Akibat pertukaran panas dengan
  lingkungannya, suhu dan tekanan di dalam tangki
  berturut-turut turun menjadi 65oC dan 400 kPa.
  Tentukan kerja lapisan batas selama proses ini.

Wb 0 karena dV 0
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Shaft Work

• Shaft Work
• Wsh 2.?.n.?
• ? torsi F.r
• Daya Poros

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Example4

• Determine the power transmitted through the
  shaft of a car when the torque applied is 200 N.m
  and the shaft rotates at a rate of 4000
  revolutions per minute (rpm).

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Example4 Solution

• The shaft power is determined directly from
• 83.8 kW (112 HP)

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Spring Work

• Spring Work
• Wsp 0.5 k (x12 x22)
• k spring constant (kN/m)
• F kx

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Work by Elastic Bars
?n normal stress ?n F/A
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Acceleration Grafitational Work
Wa 0.5 m.(V22-V12)

• Wg m.g.?z
• m.g. ?h

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Example5

• Consider a 1200-kg car cruising steadily on a
  level road at 90 km/h. Now the car starts
  climbing a hill that is sloped 30 from the
  horizontal (Fig. 235). If the velocity of the
  car is to remain constant during climbing,
  determine the additional power that must be
  delivered by the engine.

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Example5 Solution

• The additional power required is simply the work
  that needs to be done per unit time to raise the
  elevation of the car, which is equal to the
  change in the potential energy of the car per
  unit time

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Example6

• Determine the power required to accelerate a
  900-kg car shown in Fig. 236 from rest to a
  velocity of 80 km/h in 20 s on a level road.

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Example6 Solution