Module 2-2 Flashcards Preview

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Flashcards in Module 2-2 Deck (33):
1

What is moving boundary work

PdV work. work caused by moving the boundary of the system in a CM system

2

When is moving boundary work not applicable

Rigid systems (inflexible boundaries)

3

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

4

What are common path vs point functions

Energy -> point function
Work -> path function
Heat -> Path function
(W2, Q2, W1, Q1 are meaningless)

5

What are thermodynamic properties

Properties related to energy
(P,v,T,u,h,s)

6

What determines the number of independent thermo properties

# of independent TD properties = (# of reversible work modes) + 1

7

What is a simple compressible substance

substance where the only reversible work mode is PdV work

8

How many idep TD properties are there for a SCS

2 (1 reversible work mode + 1 for heat transfer)

9

What is a compressed liquid

At a given P, the T is too low to vaporize. Additional Q increases T

10

What is a saturated liquid

At a given P, the T at which adding any more Q will lead to vaporization

11

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

12

What is a saturated vapor

at a given P, the T is such that removing Q will lead to condensation

13

what is a superheated vapor

at a given P, T is high enough that removing Q will not lead to condensation

14

What is the vapor dome?

The two phase region. In the region, Lines of constant temperature are horizontal (constant P)

15

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

16

What is a saturated mixture

mixture of states in the vapor dome

17

what is the mixture quality?

x = mg/m (percent that is gas)

18

What is the mixture quality of a saturated liquid

0

19

what is the mixture quality of a saturated vapor

1

20

How do we determine TD properties within the vapor dome

y = (1-x)y_liquid + x*y_vapor

21

how can we determine the mixture quality from a property, y?

x = (y-yf)/(yg-yf) =

22

What is enthalpy?

h = u + Pv, H= U + PV

23

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

24

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)

25

what are the two ways of calculating h for a SCS?

h = u(Tsat) + P*v(Tsat),
h = h(Tsat) + v(Tsat)*(P-Psat)

26

What is the ideal gas state equation

Pv = RT

27

What is the compressibility factor and how is it used?

Z = Pv/RT. When Z is close to 1 the ideal gas law holds

28

What limitations are there for when we can assume ideal gas?

P << Pcr or T > 2*Tcr

29

What is specific heat?

the amount of energy required to raise the temperature 1K per unit mass

30

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

31

how does internal energy vary for an ideal gas

internal energy is only dependent on temperature. u = u(T)

32

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

33

How can we approximate change in enthalpy or internal energy for a system across T1->2

We can assume linear change in cv or cp. therefore
u1->2 = cvavg(T2-T1)
h1->2 = cpavg(T2-T1)