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HYDRO ELECTRIC POWER PLANT. AGUS HARYANTO. 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.

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HYDRO ELECTRIC POWER PLANT

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Hydro electric power plant

HYDRO ELECTRIC POWER PLANT

AGUS HARYANTO


Objectives

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.


Recall energy sistem termodinamika

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)


Thermodynamics concern

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.

Thechange 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.


Macroscopic vs microscopic energy

Macroscopic vs. Microscopic Energy

The macroscopicforms of energy are those a system possesses as a whole with respect to some outside reference frame, such as kinetic and potential energies.

The microscopicforms 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 byU.


More on internal energy

More on Internal Energy

SENSIBLE and LATENT energy

CHEMICAL energy

NUCLEAR energy

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


More on internal energy sensible energy

More on Internal Energy: Sensible Energy

The various forms of microscopic energies that make up sensible energy

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


More on internal energy latent energy

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 coefficientof water vaporization is 2256.5 kJ/kg.


More on internal energy chemical and nuclear energy

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.


Energy transfer heat vs works

Energy Transfer: Heat vs. Works

*) 1,2 for Clossed System; 1,2,3 for Open System

Energy crosses the boundaries in the form of:

Heat

Work

Mass flow*


Heat q

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


Work w

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.


Sign convention

Sign Convention

+

-

-

+

Qin = + (positive)

Qout = - (negative)

Win = - (negative)

Wout = + (positive)


Note on heat and work

Note on HEAT and WORK

Both are recognized at the boundaries of a system as they cross the boundaries. That is, both heat and work are boundary phenomena.

Systems possess energy, but not heat or work.

Both are associated with a process, not a state. Unlike properties, heat or work has no meaning at a state.

Both are path functions (i.e., their magnitudes depend on the path followed during a process as well as the end states), and not pointfunctions.


Path vs point functions

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.


Path vs point functions1

Path vs. Point Functions

Properties are point functions

Heat and Work are path functions


Example1

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.


Example1 solution

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.


Example2

Example2

A potato initially at room temperature (25°C) is being baked in an oven that is maintained at 200°C, as shown in Fig. 2–21. Is there any heat transfer during this baking process?


Example2 solution

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


Example21

Example2

Electrical Work: Wel = V.I.t = I.R.I.t

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.


Example3 solution 1 st case

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.


Example3 solution 2 nd case

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.


Mechanical forms of work

MECHANICAL FORMS OF WORK

Kinetical Work

Wk = F.s

Wb = P.A.ds = P.dV


Example

Example:

Wb = 0 karena dV = 0

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.


Shaft work

Shaft Work

Shaft Work

Wsh = 2..n.

 = torsi = F.r

DayaPoros:


Example4

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).


Example4 solution

Example4: Solution

The shaft power is determined directly from:

=

= 83.8 kW (112 HP)


Spring work

Spring Work

Spring Work

Wsp = 0.5 k (x12 – x22)

k = spring constant (kN/m)

F = kx


Work by elastic bars

Work by Elastic Bars

n = normal stress

n = F/A


Acceleration grafitational work

Acceleration & Grafitational Work

Wa = 0.5 m.(V22-V12)

Wg = m.g.z

= m.g. h


Example5

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. 2–35). If the velocity of the car is to remain constant during climbing, determine the additional power that must be delivered by the engine.


Example5 solution

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:


Example6

Example6

Determine the power required to accelerate a 900-kg car shown in Fig. 2–36 from rest to a velocity of 80 km/h in 20 s on a level road.


Example6 solution

Example6: Solution


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