Module 2-2

Question 1

What is moving boundary work

Answer 1

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

Question 2

When is moving boundary work not applicable

Answer 2

Rigid systems (inflexible boundaries)

Question 3

what is the difference between point functions and path functions

Answer 3

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

Question 4

What are common path vs point functions

Answer 4

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

Question 5

What are thermodynamic properties

Answer 5

Properties related to energy

P,v,T,u,h,s

Question 6

What determines the number of independent thermo properties

Answer 6

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

Question 7

What is a simple compressible substance

Answer 7

substance where the only reversible work mode is PdV work

Question 8

How many idep TD properties are there for a SCS

Answer 8

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

Question 9

What is a compressed liquid

Answer 9

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

Question 10

What is a saturated liquid

Answer 10

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

Question 11

What is a saturated mixture

Answer 11

At a given P, T is at the phase change T. Both phases exist, adding Q increases the amount of vapor

Question 12

What is a saturated vapor

Answer 12

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

Question 13

what is a superheated vapor

Answer 13

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

Question 14

What is the vapor dome?

Answer 14

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

Question 15

What is the critical point

Answer 15

The top of the vapor dome. At this pressure/temp combo, there is no observable phase change from liquid->vapor

Question 16

What is a saturated mixture

Answer 16

mixture of states in the vapor dome

Question 17

what is the mixture quality?

Answer 17

x = mg/m (percent that is gas)

Question 18

What is the mixture quality of a saturated liquid

Answer 18

0

Question 19

what is the mixture quality of a saturated vapor

Answer 19

1

Question 20

How do we determine TD properties within the vapor dome

Answer 20

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

Question 21

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

Answer 21

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

Question 22

What is enthalpy?

Answer 22

h = u + Pv, H= U + PV

Question 23

how is u defined

Answer 23

u is defined from a reference point. Due to this, we are unable to mix tables and figures as they have different reference points

Question 24

For a SCS, most TD properties are function of what other property

Answer 24

Most properties are a function of temperature alone (v,u,h,s) (although h is slightly affected by p)

Question 25

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

Answer 25

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

Question 26

What is the ideal gas state equation

Answer 26

Pv = RT

Question 27

What is the compressibility factor and how is it used?

Answer 27

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

Question 28

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

Answer 28

P << Pcr or T > 2*Tcr

Question 29

What is specific heat?

Answer 29

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

Question 30

What are the euqations for specific heat

Answer 30

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

Question 31

how does internal energy vary for an ideal gas

Answer 31

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

Question 32

how does enthalpy vary for an ideal gas

Answer 32

enthalpy is a function of u + Pv, but Pv = RT. therefore h = u(T) + RT, it is a function of T alone

Question 33

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

Answer 33

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