Energy Flashcards
What is the Internal Energy of a System?
The sum of all microscopic forms of energy: Molecular translation, rotation, vibration
It has the symbol U and is equal to m * u where m is the mass of the system and u is the specific internal energy
What is the Enthalpy of a System?
The sum of all microscopic forms of energy of a fluid in motion: Internal energy + Flow energy
It has the symbol H and is equal to m * h where m is the mass of the system and h is the specific enthalpy.
h = u + Pv
u = Specific Internal Energy
P = Pressure
v = Specific Volume
What is the Kinetic Energy of a System?
A macroscopic form of energy that quantifies energy relative to the velocity.
1/2 * m * v^2
What is the Potential Energy of a System?
A macroscopic form of energy which quantifies energy relative to it’s elevation relative to a reference.
m * g * h
What is the equation for the total energy of a system?
e = u + Pv + ke + pe
e = u + mechanical energy
E = H + KE + PE
What is the Bernoulli Equation?
(Pressure / Density) + (Velocity^2 / 2) + (Gravitational Field Strength * Relative Height) = Constant
When is the Bernoulli Equation valid?
- The fluid must be incompressible (Density doesn’t change)
- There is no heat or work transfer
- There is no losses (The fluid isn’t viscous)
What are the main ways to transfer energy?
- Heat
- Work
- Via Mass Transfer
What is the equation for total heat transfer?
Q = Q dot * Delta t
The total heat transfer is equal to the rate of heat transfer multiplied by the time of transfer if the rate is constant
What is the equation of displacement work?
W = F * x
Work done = Force * Distance travelled
What is the equation for boundary work?
W = P * dV
Work done = Pressure * Change in Volume
What is the equation of shaft work?
W = Tau * Delta Theta
Tau = Force * Radius
Delta x = Radius * Delta Theta
What is the equation for electrical work?
P = V * I
Power = Voltage * Current
What is the equation for spring work?
Work done = 1/2 * Spring Constant * ((Distance After)^2 - (Distance Before)^2)
What do both the heat and work depend on?
Both heat and work depend on the process, not the states
How can we apply the first law of thermodynamics to the mass flow in an open system?
Because energy is conserved, then the energy flowing into the system minus the energy flowing out of the system is equal to the energy change within the system
What is the equation of efficiency?
Efficiency = Desired Output / Required Input
