Thermodynamics introduction
Dr. Asiri Indrajith
Asiri.Kulathunga@gmail.com
0716367129
Saturday, 16 October 2021
Introduction
Thermodynamic systems
What is thermodynamics
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•
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The science of energy that concerns with the ways in which the energy is
stored within a body.
Energy transformation- mostly involve heat and work movement
The fundamental law is the conservation of energy principle: energy cannot
be created or destroyed, but can only be transformed from one form to
another
Introduction
Thermodynamic systems
Heat
Is a form or energy which is transferred from one body to
another body at a lower temperature. For example, when
there is a body with certain temperature around 30 degrees, is
brought int contact with the body B at a lower temperature
body B. the there will be a heat transfer in-between two
bodies until the temperature of A and B are equal. When they
come to a same temperature there is no heat transfer between
bodies, and they are said to be in thermal equilibrium.
Introduction
Thermodynamic systems
Microscopic and macroscopic thermodynamics
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Microscopic thermodynamics:
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All the atoms and molecules of the system are considered and the summation of all the and
molecules are used. It is statistical approach of thermodynamics
Macroscopic thermodynamics
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When matter are considered as continuos function of space variable. It is classical approach of
thermodynamics, which requires simple mathematical formula for analyzing the system.
Introduction
Thermodynamic systems, surrounding and boundary
System:
Collection of matter within prescribed and identifiable boundaries
Open system
System in which there is a transfer of mass across the boundaries
Introduction
Thermodynamic systems, surrounding and boundary
Pressure of the system:
The pressure of the system is the force exerted by the system on unit area on its boundaries. Here
pressure is defined as the absolute pressure. N/m2 or Pa and Bar
Absolute, gauge and vacuum pressure:
Actual pressure at a given point is called as absolute pressure
Most pressure gauge devices care calibrated the value relative to the
atmospheric pressure. Therefore, that gives the gauge pressure
𝑷𝒈𝒖𝒂𝒈𝒆 = 𝑷𝒂𝒃𝒔 − 𝑷𝒂𝒕𝒎
Pressure below atmospheric pressure are called vacuum pressure
Introduction
Thermodynamic systems, surrounding and boundary
Introduction
Thermodynamic systems, surrounding and boundary
A vacuum gauge is connected to a chamber which reads 0.2 Bar at a
location where the atmospheric pressure is 1.02 Bar. Determine the
absolute pressure in the chamber.
Introduction
Thermodynamic systems, surrounding and boundary
• Variation of pressure with depth.
• P= h.z.g
• Pressure difference between two points in a
constant density fluid is proportional to the vertical
distance between the points. Same height points
has same pressure.
Introduction
Systems properties
Introduction
Systems properties
Work:
Is defined as the product of a force and the distance moved in the direction
of the force. When the boundary of a closed system moves in the direction
of the force acting on it, then the surroundings do work on the system.
When the boundary is moved outwards the work is done by the system on
the surrounding. The unit of the work is Nm.
Introduction
Systems properties
Heat and work are transitory energies and must not confused with
intrinsic energy possessed by a system. For example, when a gas contained
in a well lagged cylinder is compressed by moving the piston to the left,
the pressure and temperature of the gas are observed to increase, and
hence the intrinsic energy of the gas increases. The intrinsic energy
increase in the gas has been caused by the work done by the piston on the
gas.
Introduction
Systems properties
Consider a gas contained in a rigid container and heated, since the
boundaries of the system are rigidly fixed then no work is done on or by
the system. The pressure and temperature of the gas are observed to
increase, and hence the intrinsic energy of the gas will increase. The
increase in intrinsic energy has been caused by the heat flow to the system
Introduction
MCQ
1. Select the correct statement
1.
2.
3.
4.
Both molecular weight and total weight of a gas are intensive properties
Both molecular weight and total weight of a gas are extensive properties
Total weight of a gas is an extensive property molecular weight is an intensive property
Total weight of a gas is an intensive property molecular weight is an extensive property
2. The internal energy of a substance
1.
2.
3.
4.
decreases with increase in temperature
increases with increase in temperature
remains unaffected with change in temperature
can be calculated by the relation E = mc2
Introduction
Thermodynamic systems
Thermometer and thermometric property
Thermometer and thermometric property
Introduction
Thank you