Lectures 4-7 Flashcards
Internal Energy is…
Sum of all of the microscopic forms of energy
Boundary work is…
Work associated with the system boundary changing shape
Equation for boundary work
W b = P * change in V
Boundary W = pressure * change in volume
The general equation for boundary work
W b = integral ( P dV )
Boundary W = integral (pressure * change in volume)
Enthalpy combines…
Denoted by letter…
Internal energy and Boundary work
H
Enthalpy should be used for systems with a …
CHANGING volume
On the other hand, internal energy should be used for systems with a…
FIXED volume
Base equation of enthalpy
H = U + W b
Enthalpy = internal energy + Boundary work
Equation for enthalpy subbing in for the Boundary work equation
H = U + PV
Enthalpy = Internal energy + (pressure * volume)
First Law of Thermodynamics
Energy can neither be created or destroyed; it can only change forms
An energy balance is when you …
find the difference in the sums of all the energy going into the system as well as those leaving the system.
When carrying out an energy balance equation, we must remember to account for the energy associated with
mass
When considering a stationary system energy balance equation, what can we assume as 0… This leaves only —, — and — to consider.
Kinetic and all potential energies
Mass, work and heat
What interactions affect the energy content of a control volume/system?
As well as mass flow, heat and work
When analysing a closed system what term can we remove from the energy balance equation
mass term as it is a closed system where no mass crosses the system boundary
Closed system energy balance equation is
E system = Q net + W net
E system = change in U (change in internal energy)
as change in U = Q net + W net (net thermal energy and net work done)
When a system runs in a cycle, what must return to its original state
The working fluid
Efficiency in terms of a system measures what
how well an energy transfer or conversion has been carried out
Specific heat capacity is defined as
the amount of energy required to raise the temperature of a unit mass of substance by one degree
In thermo module, the two types of specific heat are
c v (constant volume) and c p (constant pressure)
For solids and vapours are there two different values for specific heat?
No
State specific heat capacity at constant volume
The amount of energy required to raise the temperature of a unit mass by 1K (or 1 degree C) with the volume being held constant.
Equation for specific heat capacity at constant volume, to derivation of final equation using the 1st Law of Thermodynamics
- c v = ( change in q / change in T ) v
- 1st law of thermo Q 1-2 = U2 - U1 + W 1-2
- Work term would be zero as the volume stays constant with NO boundary work so Q 1-2 = U2 - U1 (+ 0)
- So change in q = change in u (q is thermal energy and u is internal energy)
- c v = ( change in u / change in T ) v
What are the units for specific heat cap at constant vol
kJ/kg・K
