thermo

1. Basic Principles and Concepts of
Thermodynamics
Definitions, Systems, States, Processes, Properties, System of Units, and
the Laws of Thermodynamics

2. Systems and Control Volumes
• A System is defined as a “quantity of matter or a region in space chosen for
study”.
• The Surroundings is the mass or region outside the system
• The real or imaginary surface that separates the system from the surroundings
is called the Boundary.

3. Types of Systems
1. Closed System- or Control Mass, is a system wherein no mass can cross
the boundary, but work or energy can. It contains a fixed
mass.
2. Open System- or Control Volume, is a system that involves mass flow and
energy flow. Some examples are turbines, pumps, boilers,
etc.

4. Properties of a System
1. Intensive Properties- these are the properties that are independent of the
mass of the system. Some examples are temperature,
pressure and density.
2. Extensive Properties- properties that are dependent of the size, or extent of
the system. Mass, length, and volume are a few
examples.
State of a System
• The condition of a substance or a system is defined by thermodynamic
properties. However, the term “condition” is not acceptable in
thermodynamics. We use the term State.
• By knowing the thermodynamic properties of a substance or a system, we can
know its state.
• According to the state postulate, “The state of a simple compressible system is
completely specified by two independent, intensive properties”.

5. Processes and Quasi Equilibrium Processes
• Any change a system undergoes from one equilibrium state to another is
called a process.
• The series of states through which a system passes during a process is called
the path.
• Quasi-Static or Quasi-Equilibrium Processes are processes that proceeds in
such a manner that the system remains infinitesimally close to an equilibrium
state at all times.
• This can be viewed as a very slow process that allows the system to adjust
itself internally so that the properties of one part does not change any faster
than others.

6. Laws of Thermodynamics
1. The 1st Law of Thermodynamics deals with the conservation of energy. It
states that energy can neither be created nor destroyed; it only transforms
from one form to another.
2. The 2nd Law of Thermodynamics deals with the direction of flow of heat
energy. It states that heat flows from a higher temperature body to lower
temperature one. It also states that the net entropy of the universe will
always increase.
3. The 3rd Law of Thermodynamics states that the entropy of a perfect crystal
at absolute zero is exactly equal to zero.
4. The Zeroth Law is the law concerning thermal equilibrium. The law states
that when two bodies are each in thermal equilibrium with some third
body, then they are also in equilibrium with each other.

7. System of Units, Conversion Ratios and Thermodynamic Properties
• Any physical quantity can be characterized by dimensions. The magnitude assigned to these
dimensions are called units.
• Dimensions can be grouped into two, namely primary and secondary or derived dimensions.
Dimension (Primary) Unit
Mass kilogram (kg)
Length meter (m)
Time second (s)
Temperature kelvin (K)
Electrical Current ampere (A)
Amount of Light candela (cd)
Amount of Matter mole (mol)

8. 1. Mass and Weight

9. 1. Mass and Weight
• Mass is the absolute quantity of matter in a substance or body.
• Weight is the force of gravity on the body and could be determined by devices such as
weighing scales and springs. This quantity changes with gravity.
• Newton’s 2nd law of motion states that the acceleration of a particular body is directly
proportional to the force exerted on it and inversely proportional to the mass.
𝑎 ∝
𝐹
𝑚
𝑜𝑟 𝑎 = 𝑘
𝐹
𝑚
𝑜𝑟 𝐹 =
𝑚𝑎
𝑘
Unity value for k Non unity value for k
1
𝑔 𝑚 ∙ 𝑐𝑚
𝐷𝑦𝑛𝑒 ∙ 𝑠2 981
𝑔 𝑚 ∙ 𝑐𝑚
𝑔 𝑓 ∙ 𝑠2
1
𝑘𝑔 𝑚 ∙ 𝑚
𝑁 ∙ 𝑠2 9.81
𝑘𝑔 𝑚 ∙ 𝑚
𝑘𝑔 𝑓 ∙ 𝑠2
1
𝑠𝑙𝑢𝑔 ∙ 𝑓𝑡
𝑙𝑏𝑓 ∙ 𝑠2
32.2
𝑙𝑏 𝑚 ∙ 𝑓𝑡
𝑙𝑏𝑓 ∙ 𝑠2

10. 2. Density
• An intensive property defined as mass per unit volume.
𝜌 =
𝑚
𝑉
Where 𝜌= density of the substance,
𝑘𝑔 𝑚
𝑚3 𝑜𝑟
𝑙𝑏 𝑚
𝑓𝑡3
𝑚= mass of the substance, 𝑘𝑔 𝑚 𝑜𝑟 𝑙𝑏 𝑚
𝑉= volume of the substance, 𝑚3
𝑜𝑟 𝑓𝑡3
3. Specific Volume
• It is the volume of a unit mass. It is the inverse or reciprocal of density.
ν =
𝑉
𝑚
=
1
𝜌
Where ν= specific volume of the substance,
𝑚3
𝑘𝑔 𝑚
𝑜𝑟
𝑓𝑡3
𝑙𝑏 𝑚

11. 4. Specific Weight
• Specific weight is the force of gravity per unit volume.
𝛾 = 𝜌𝑔
5. Specific Gravity
• This is the ratio of the specific weight or density of a substance to water
(if liquid) or to air (if gas).
𝑆𝐺 =
𝜌
𝜌 𝑤
=
𝛾
𝛾 𝑤
𝑜𝑟
𝜌
𝜌 𝑎
=
𝛾
𝛾𝑎

12. Sample Problems
1. The weight of an object is 100 lbf. Determine its mass standard conditions.
2. Find the weight of an object with 50 lbm at sea level.
3. Determine the specific weight of water at standard conditions, in kgf/m3 and lbf/ft3.
4. Two liquids of different densities ρ1=1500 kg/m3, ρ2=500 kg/m3, were poured together into a
100 liter container, filling it. If the resulting density of the mixture is 800 kg/m3, find the
respective amounts of the liquids used. Also, find the weight of the mixture in kgf; local
g=9.675 m/s2.
5. A cylinder 3 inches in radius and 10 inches in height contains oil that has a density of 850
kgf/m3. Determine the weight of the oil in lbf.
6. The fuel tank of a car holds 60 L of gasoline. Assuming that the gasoline has a specific gravity of
0.74, determine the weight of the gasoline in the tank, in kgf.
7. A liquid has a specific weight of 200 lbf/ft3. Calculate the volume needed to have a weight of
390 lbf.
8. Gasoline has a density of 1.3 slugs per cubic feet. What is the weight of 60 L of gasoline?
9. If a tank can hold 275 gallons of oil, and oil has a specific weight of 8,800 N/m3, how many
pounds of oil will there be in a full tank?