chap 3
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my thermo great teaching materialTRANSCRIPT
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3
MV 2011– THERMODYNAMICS
Introduce the concept of energy and define its various forms.
Discuss the nature of internal energy.
Define the concept of heat and the terminology associated with energy transfer by heat.
Define the concept of work, including electrical work and several forms of mechanical work.
Introduce the first law of thermodynamics, energy balances, and mechanisms of energy transfer to or from a system.
*
*
An expression of THE 1ST LAW OF THERMO DYNAMICS
*
*
INTRODUCTION
“Energy can not be created nor can be destroyed there is only the transformation of one form to another”
In other word “the energy of whole universe is remain constant”
It gives relation b\n heat supplied & work done
U = Q - W
*
*
[email protected]
Q = U + W
thermal,
mechanical,
kinetic,
potential,
electric,
magnetic,
chemical,
nuclear …
[email protected]
FORMS OF ENERGY
Forms of energy that make up the total energy of a system can be grouped in two:
The macroscopic forms of energy are those a system possesses as a whole WRT some outside reference frame,
e.g. 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 U of a system.
*
*
[email protected]
the sum of all the microscopic forms of energy of a system.
related to the molecular structure and the degree of molecular activity and can be viewed as the sum of the kinetic and potential energies of the molecules.
sensible energy
latent energy
chemical energy
nuclear energy
HEAT & WORK
*
*
Defense Engineering, college, DEC
ENERGY TRANSFER BY HEAT
HEAT is energy (thermal) in transit, energy that transfers from one body to another because of temperature difference.
Heat flows from an area of high temperature to an area of low temperature (unless an external work is done).
Heat is measured with the following SI units:
joules (J); calorie (cal); kilocalorie (kcal or Cal)
where: 1 cal = 4.184J and 1 Cal = 1000cal
*
*
*Thermal conductivity – ability of a material to allow
heat to pass through
2. CONVECTION – heat transfer through fluids (liquids and gases), which involves currents/flow
3. RADIATION – heat transfer through empty space, through electromagnetic radiation, such as light, microwave, etc.
*
*
Defense Engineering, college, DEC
ENERGY TRANSFER BY WORK
Work is an energy interaction between a system and its surroundings.
If the energy crossing the boundary of a closed system is not heat, it must be work.
*
*
For Heat (Q)
For Work (W)
*
*
Electrical
Magnetic
*
*
[email protected]
Mechanical energy is the form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device such as an ideal turbine.
[email protected]
*
*
ΔU= - W
ΔU= Q
Isothermal: constant temperature
3
MV 2011– THERMODYNAMICS
Introduce the concept of energy and define its various forms.
Discuss the nature of internal energy.
Define the concept of heat and the terminology associated with energy transfer by heat.
Define the concept of work, including electrical work and several forms of mechanical work.
Introduce the first law of thermodynamics, energy balances, and mechanisms of energy transfer to or from a system.
*
*
An expression of THE 1ST LAW OF THERMO DYNAMICS
*
*
INTRODUCTION
“Energy can not be created nor can be destroyed there is only the transformation of one form to another”
In other word “the energy of whole universe is remain constant”
It gives relation b\n heat supplied & work done
U = Q - W
*
*
[email protected]
Q = U + W
thermal,
mechanical,
kinetic,
potential,
electric,
magnetic,
chemical,
nuclear …
[email protected]
FORMS OF ENERGY
Forms of energy that make up the total energy of a system can be grouped in two:
The macroscopic forms of energy are those a system possesses as a whole WRT some outside reference frame,
e.g. 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 U of a system.
*
*
[email protected]
the sum of all the microscopic forms of energy of a system.
related to the molecular structure and the degree of molecular activity and can be viewed as the sum of the kinetic and potential energies of the molecules.
sensible energy
latent energy
chemical energy
nuclear energy
HEAT & WORK
*
*
Defense Engineering, college, DEC
ENERGY TRANSFER BY HEAT
HEAT is energy (thermal) in transit, energy that transfers from one body to another because of temperature difference.
Heat flows from an area of high temperature to an area of low temperature (unless an external work is done).
Heat is measured with the following SI units:
joules (J); calorie (cal); kilocalorie (kcal or Cal)
where: 1 cal = 4.184J and 1 Cal = 1000cal
*
*
*Thermal conductivity – ability of a material to allow
heat to pass through
2. CONVECTION – heat transfer through fluids (liquids and gases), which involves currents/flow
3. RADIATION – heat transfer through empty space, through electromagnetic radiation, such as light, microwave, etc.
*
*
Defense Engineering, college, DEC
ENERGY TRANSFER BY WORK
Work is an energy interaction between a system and its surroundings.
If the energy crossing the boundary of a closed system is not heat, it must be work.
*
*
For Heat (Q)
For Work (W)
*
*
Electrical
Magnetic
*
*
[email protected]
Mechanical energy is the form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device such as an ideal turbine.
[email protected]
*
*
ΔU= - W
ΔU= Q
Isothermal: constant temperature