Lecture 1 Flashcards
What is a system?
A system describe precisely what is being studied
Control mass or control volume
What is the surroundings to a system?
Everything external to the system
What is a systems boundary?
A boundary distinguishes a system from its boundaries
What is a closed system?
A control mass is under study where no mass would cross the boundary
m = constant, Energy can cross the boundary
What is an isolated system?
A special type of system that does not interact in any way with its surroundings is called an Isolated system
No mass & energy would cross any other part of the boundary
What is an open system?
A control volume is under study where mass may flow through the boundary
both mass and energy can cross the boundary
Define properties of a system
A macroscopic characteristic of a system such as mass, volume, energy, pressure and temperature to which a numerical value can be assigned at a given time without knowledge of the previous behavior (history) of the system
What is an extensive property?
A property where its value for an overall system is the sum of its values for the parts into which the system is divided
What is a state of a system?
The conditions of system as described by its properties
What is an Intensive Property?
Properties that are not additive. Independet of size or extent of a system and may vary from place to place within the system at any moment.
What is steady state?
No property change with time
What defines a process
A process starts with a property changeing and ends with a change of the state
What is equilibrium?
A state of balance where no natural processes can happen
No unbalenced forces in the system
Define Temperature
Measures a body´s thermal state.
Measures the state of movement of molecules and atoms. When the movement “ceases” the temperature is the lowest. This is an absolute zero of temperature.
What is the 0th law of thermodynamics?
If objects A and B are separately in contact with a third object C, then A and B are in thermal equilibrium with each other if they are both in thermal equilibrium with object C
Define the principle Thermal expansion
Thermometer
The volume expansion (or pressure increase) of a (ideal) gas gives the same scale as the thermodynamic temperature scale.
What is thermal equilibrium?
two objects that have the same temperature are in thermal equilibrium
Define the principle Blackbody radiation
Thermometer
All objects above absolute zero emit blackbody radiation for which the spectra is directly proportional to the temperature.
What is pressure?
Pressure is force per unit area, P=F/A
SI pressure units
1 Pa = 1 N/m^2
1 bar = 10^5 Pa = 100 kPa
1 atm = 1.013 bars = 14.7 psi
Define Absolute Pressure
Pressure with respect to the zero pressure of a complete vacuum.
How can you measure pressure?
With barometer and manometers the pressure becomes hight of a column of liquid
What is Specific Volume?
𝑣 =1/𝜌
Unit: m3/kg
What is the connection between energy and work?
W = ΔEk = ΔEp
Sign convention, apply it on work and heat (W, Q).
W>0: work done by the system
W<0: work done on the system
Q > 0 heat transfer to the system
Q < 0 heat transfer from the system
What is work?
Work = force * distance
[J] or [Nm]
What is specific work?
ε = W/m
What is Power?
P = dW/dt = ∫ pressure* dVolym
Rate of energy transfer by work
What is a Quasiequilibrium process?
The process is considered a series of equilibrium states,
i.e. “almost static”
The process is reversible.
The work can be evaluated in terms of changes in system
state
What is internal energy U
Energy attributed to the motions and configurations of the
individual molecules, atoms, and subatomic particles making up the matter in the system
U [J], u [J/kg]
Write an expression for total energy
E = Ek + Ep + U
What defines energy transfer by heat?
Energy exchange between bodies caused by a temperature difference
Q
Name 3 types of heat tranfer
Conduction
Convection
Radiation
