Exam 1 Ch.1-3 Flashcards
Thermodynamics
The science of energy
Energy
The ability to cause changes
Conservation of energy principle
During an interaction, energy can change from one form to another, but the total amount of energy remains constant. That is, energy cannot be created or destroyed.
Change in E
Change in E = Ein - Eout
First law of thermodynamics
An expression of the conservation of energy principle, it asserts that energy is a thermodynamic property
Second Law of thermodynamics
Asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy
Classical Thermodynamics
A macroscopic approach to the study of thermodynamics that does not require a knowledge of the behavior of individual particles. It provides a direct and easy way to solve engineering problems.
Units
Magnitudes assigned to dimensions
Dimensions
Any physical quantity
Derived units
velocity, energy, volume, expressed in terms of the primary dimensions and are called secondary dimensions or derived dimensions
Primary / Fundamental dimensions
length (meter), mass (kilogram), time (second), temperature (kelvin), electric current (ampere), amount of light (candela), amount of matter (mol)
pound-force (lbf)
the force required to accelerate a mass of 1 slug at a rate of 1 ft/s^2
Weight
he gravitational force applied to a body, its magnitude is determined from Newton’s Second Law, W=m*g where m is mass, g is the gravitational acceleration (g is 9.807 m/s^2 or 32.174 ft/s^2
Work
A form of energy, can simply be defined as force times distance
Joule
= 1 N*m
BTU (British Thermal Unit)
The energy required to raise the temperature of 1 lbm of water at 68F by 1F.
Calorie
the amount of energy needed to raise the temperature of 1g of water at 14.5C by 1C.
Watt
J/s, unit for time rate of energy, in the case of work, the time rate of energy is called power
1 kg m/s^2
Newton
Surroundings
The mass or region outside the system
Boundary
The real or imaginary surface that separates the system from its surroundings (can be fixed or movable) Has zero thickness
Closed System (Control Mass)
Consists of a fixed amount of mass, and no mass can cross its boundary, no mass can enter or leave. Energy in the form of heat or work can cross the boundary and the volume does not have to be fixed.
Isolated system
Closed system where energy is not allowed to cross the boundary
Open system (Control volume)
Usually encloses a device that involves mass flow such as a compressor, turbine, or nozzle. Both mass and energy can cross the boundary of a control volume.
Property
Any characteristic of a system Ex: pressure, temp, volume, mass, viscosity, thermal conductivity, etc.
Intensive properties
Properties independent of the mass of a system, such as temperature, pressure, and density
Extensive Properties
Properties that depend on the size - or extent - of the system. Total mass, total volume, total momentum
Specific Properties
Extensive properties per unit mass Ex: specific volume
Continuum
Continuous, homogeneous matter with no holes
Density
Mass per unit volume
Specific Volume
The reciprocal of density, volume per unit mass
Specific Gravity (Relative density)
the ratio of the density of a substance to the density of some standard substance at a specified temperature
State
A set of properties that completely describes the condition of the system at a specific time
Equilibrium
Implies a state of balance. There are no unbalanced potentials or driving forces within the system
