Flashcards in Module 2-2 Deck (33):
What is moving boundary work
PdV work. work caused by moving the boundary of the system in a CM system
When is moving boundary work not applicable
Rigid systems (inflexible boundaries)
what is the difference between point functions and path functions
With a point function, knowing the end of the points is enough to determine the value of the integral. With path functions we need the entire path to determine the total amount added
What are common path vs point functions
Energy -> point function
Work -> path function
Heat -> Path function
(W2, Q2, W1, Q1 are meaningless)
What are thermodynamic properties
Properties related to energy
What determines the number of independent thermo properties
# of independent TD properties = (# of reversible work modes) + 1
What is a simple compressible substance
substance where the only reversible work mode is PdV work
How many idep TD properties are there for a SCS
2 (1 reversible work mode + 1 for heat transfer)
What is a compressed liquid
At a given P, the T is too low to vaporize. Additional Q increases T
What is a saturated liquid
At a given P, the T at which adding any more Q will lead to vaporization
What is a saturated mixture
At a given P, T is at the phase change T. Both phases exist, adding Q increases the amount of vapor
What is a saturated vapor
at a given P, the T is such that removing Q will lead to condensation
what is a superheated vapor
at a given P, T is high enough that removing Q will not lead to condensation
What is the vapor dome?
The two phase region. In the region, Lines of constant temperature are horizontal (constant P)
What is the critical point
The top of the vapor dome. At this pressure/temp combo, there is no observable phase change from liquid->vapor
What is a saturated mixture
mixture of states in the vapor dome
what is the mixture quality?
x = mg/m (percent that is gas)
What is the mixture quality of a saturated liquid
what is the mixture quality of a saturated vapor
How do we determine TD properties within the vapor dome
y = (1-x)y_liquid + x*y_vapor
how can we determine the mixture quality from a property, y?
x = (y-yf)/(yg-yf) =
What is enthalpy?
h = u + Pv, H= U + PV
how is u defined
u is defined from a reference point. Due to this, we are unable to mix tables and figures as they have different reference points
For a SCS, most TD properties are function of what other property
Most properties are a function of temperature alone (v,u,h,s) (although h is slightly affected by p)
what are the two ways of calculating h for a SCS?
h = u(Tsat) + P*v(Tsat),
h = h(Tsat) + v(Tsat)*(P-Psat)
What is the ideal gas state equation
Pv = RT
What is the compressibility factor and how is it used?
Z = Pv/RT. When Z is close to 1 the ideal gas law holds
What limitations are there for when we can assume ideal gas?
P << Pcr or T > 2*Tcr
What is specific heat?
the amount of energy required to raise the temperature 1K per unit mass
What are the euqations for specific heat
cv = dU/dT at constant v
cp = dh/dT at constant P.
Note: v or p do not need to be constant in order to use cv and cp
how does internal energy vary for an ideal gas
internal energy is only dependent on temperature. u = u(T)
how does enthalpy vary for an ideal gas
enthalpy is a function of u + Pv, but Pv = RT. therefore h = u(T) + RT, it is a function of T alone