Ting Wang Thermo 1 Final Review

Studied by 18 people
5.0(1)
get a hint
hint

1 Pascal = __ N/m²

1 / 44

Tags and Description

UNO Ting Wang ENME 2770: Engineering Thermodynamics 1

45 Terms

1

1 Pascal = __ N/m²

1 N/m²

New cards
2

1 bar = __ Pa

10^5 Pa

New cards
3

1 atm = __ psi ~ __ bars

14.7 psi

1.013 bars

New cards
4

1 torr = __ mmHg

1 mmHg

New cards
5

When pressure decreases, the water’s freezing temperature:

a) increases

b) decreases

c) does not change

a

New cards
6

When the pressure increases, the water vapor’s condensing temperature:

a) increases

b) decreases

c) does not change

a

New cards
7

When the pressure is reduced below the saturated pressure at a given temperature, the liquid will:

a) boil

b) flash

c) does not change

b

New cards
8

Which equations are not correct for an ideal gas?

a) PV = mRT

b) Pv = nRT

c) PV = nRT

d) PV = n(universal R)T

c) pv = nRT

b and c

New cards
9

In the P-T (phase) diagram, what is the major difference between a substance contracting when freezing and another expanding on freezing. Show these two diagrams.

The curve between liquid and solid has a negative slope for a substance expanding during freezing and a positive slope for a substance contracting during freezing.

New cards
10

Define quality for a liquid-vapor mixture.

Quality is the percentage of vapor in a 2-phase mixture.

New cards
11

Write an equation to show how to use the property values of saturated liquid and saturated vapor to find internal energy (u) of liquid-vapor mixture with a quality x.

u = u_f + x * (u_g -u_f)

New cards
12

Why would a liquid on the left side of a vapor dome be called a “compressed” liquid?

The actual pressure is greater than the saturated pressure

New cards
13

Why would a liquid on the left side of a vapor dome be called a “subcooled” liquid?

The actual temperature is less than the saturated temperature

New cards
14

What are the 4 polytropic processes? And what are their n values?

1. isobaric: n=0 → P=C

2. isothermal: n=1 → T=C

3. isometric: n=infinity → V=C

4. isentropic: n=k → S=C, adiabatic, reversible

New cards
15

What is the function of a generalized compressibility factor (Z) chart?

to show deviation of areal gas from the ideal gas via the compressibility factor Z

New cards
16

Write the equations for Z, P_R, and T_R from the compressibility chart

Z = (RT) / (PV)

P_R = P / P_C

T_R = T / T_C

New cards
17

After a subsonic flow goes through a diffuser, the pressure:

a) increases

b) decreases

c) does not change

a

New cards
18

True/False

The Clausius statement says that it is impossible to transfer energy from a cooler body to a hotter body.

False

New cards
19

True/False

The perpetual motion machine of the third kind does not violate either the first or second laws of thermodynamics.

True

New cards
20

An inventor claims his invention delivers a thermal efficiency of 100%. This claim:

a) violates the 1st law

b) violates the 2nd law

c) violates both the 1st and 2nd laws

d) doesn’t violate either law

b

New cards
21

The black serpentine tube behind the refrigerator functions as a(n):

a) evaporator

b) condenser

c) compressor

d) expander

b

New cards
22

The indoor heat exchanger of a heat pump system functions as a(n):

a) evaporator

b) condenser

c) compressor

d) expander

b

New cards
23

The indoor heat exchanger of an air conditioning system functions as a(n):

a) evaporator

b) condenser

c) compressor

d) expander

a

New cards
24

Indicate changes (increase, decrease, or remains the same) of the following parameters after a supersonic flow goes through an adiabatic divergent duct:

velocity

Pressure

mass flow rate

total enthalpy

velocity: increases

Pressure: decreases

mass flow rate: does not change

total enthalpy: does not change

New cards
25

List the conditions that lead to the Bernoulli equation from the energy conservation equation.

1. no work

2. no heat transfer

3. no temperature change

New cards
26

What are the 7 values (or aspects, features) of the thermodynamic 2nd law.

1. determine whether any process is possible or not

2. predict which direction a spontaneous process will go

3. determine the theoretical max value for the: work that could be obtained, efficiency of a heat engine, COP of a refrigerator or heat pump

4. evaluate quantitatively the factors that preclude attaining the max coefficient

5. determine a thermodynamic temperature scale that is independent of physical properties, leading to Q_H/Q_C = T_H/T_C

6. correlate physical properties

7. quantify the grade of energy using the concept of entropy

New cards
27

What is the Kelvin-Planck 2nd law of thermodynamics?

It is impossible for any device operating in a cycle to absorb heat from a single reservoir and produce an equivalent amount of work.

efficiency =/= 100%

New cards
28

What are the two main purposes for employing a diffuser and a nozzle respectively?

Diffuser - increase pressure, decrease velocity

Nozzle - decrease pressure, increase velocity

New cards
29

Provide two examples of applications for a diffuser and a nozzle.

Diffuser:

1. Infront of a jet engine to convert high-velocity air stream to high pressure

2. Iin the back of a land-based gas turbine to recover exhaust gas kinetic energy as increased pressure

Nozzle:

1. Behind a jet engine to produce thrust

2. to produce low pressure suction to suck water as in a jet pump

New cards
30

Explain the function of a throttling process.

allows us to reduce temperature more than you would normally be able to

New cards
31

Give an example of a device that uses a throttling process.

Deep freezers → like for dry ice

New cards
32

What is the wet-vapor Carnot refrigeration/Heat pump cycle? What are the COP equations?

1→ 2: Compressor: isentropic (Q=0, W_in)

2→ 3: Condenser: isothermal/isobaric (W=0, Q_H,out)

3→ 4: Turbine: isentropic (Q=0, W_out)

4→ 1: evaporator: isothermal/isobaric (W=0, Q_C,in)

COP (ref) = Q_C / (Q_H - Q_C) = T_C / (T_H - T_C)

COP (heat) = Q_H / (Q_H - Q_C) = T_H / (T_H - T_C)

New cards
33

What is the gas Carnot power cycle? What is the efficiency equation?

1→ 2: isentropic compression (Q=0, W_in)

2→ 3: isothermal expansion (Q_in, W_out)

3→ 4: isentropic expansion (Q=0, W_out)

4→ 1: isothermal compression (Q_out, W_in)

Eff = 1 - (Q_out / Q_in) = 1 - (T_C / T_H)

New cards
34

What is the wet-vapor Carnot power cycle? What is the efficiency equation?

1→ 2: Compressor; isentropic (Q=0, W_in)

2→ 3: Boiler; isothermal/isobaric (W=0, Q_in)

3→ 4: Turbine; isentropic (Q=0, W_out)

4→ 1: Condenser; isothermal/isobaric (W=0, Q_out)

Eff = 1 - (Q_out / Q_in) = 1 - (T_C / T_H)

New cards
35

What is the gas refrigerant/heat pump Carnot power cycle? What are the COP equations?

1→ 2: isentropic compression (Q=0, W_in)

2→ 3: isothermal compression (Q_H,out, W_out)

3→ 4: isentropic expansion (Q=0, W_out)

4→ 1: isothermal expansion (Q_C,in, W_in)

COP (ref) = Q_C / (Q_H - Q_C) = T_C / (T_H - T_C)

COP (heat) = Q_H / (Q_H - Q_C) = T_H / (T_H - T_C)

New cards
36

How does a vortex tube work?

Pressurized gas is injected tangentially into a swirl chamber and accelerated to a high rate of rotation. The gas then travels down a tube in a vortex. Due to a conical nozzle at the end of the tube, only the outer most layer of compressed gas can escape. The rest of the gas is forced to return in an inner vortex.

New cards
37

What is relative pressure? What is it useful for?

the ratio of pressure to some reference condition, it can be found in the steam tables

it makes finding property values (pressure) much easier and faster

P2 / P1 = (P_R @ T_2) / (P_R @ T_1)

New cards
38

What is availability (Exergy)?

a measure of departure of the state of the system from that of the environment

maximum available energy to the system

New cards
39

When the system becomes equalized with the environment

New cards
40

What is irreversibility?

I = W_max - W_act = T_o (entropy production)

New cards
41

What is exergy destruction and losses?

represents lost work potential, is also called irreversibility or lost work.

(+) for any irreversible process

(0) for any reversible process

New cards
42

What does (1 - T_o / T_b) represent?

This represents the amount of available energy when multiplied by Q_j.

(T_o / T_b) is a ratio of unavailable energy to total energy

New cards
43

What is the difference between 2nd law efficiency and 1st law efficiency?

2nd law efficiency unavailable energy into consideration whereas 1st law efficiency does not.

New cards
44

What does each term mean in the below equation?

delta s = s(T_2) - s(T_1) - R ln(P_2 / P_1)

• delta s → change in entropy

• s(T_2) - s(T_1) → entropy difference at the same pressure (1 atm)

• R ln(P_2 / P_1) → pressure correction

New cards
45

The only processes that can occur are those for which the entropy of an isolated system _____.

increases

New cards

Explore top notes

Note
Studied by 33 people
Updated ... ago
5.0 Stars(2)
Note
Studied by 25 people
Updated ... ago
5.0 Stars(1)
Note
Studied by 4 people
Updated ... ago
5.0 Stars(1)
Note
Studied by 26 people
Updated ... ago
5.0 Stars(1)
Note
Studied by 8 people
Updated ... ago
5.0 Stars(1)
Note
Studied by 6 people
Updated ... ago
5.0 Stars(1)
Note
Studied by 32 people
Updated ... ago
5.0 Stars(2)
Note
Studied by 356 people
Updated ... ago
5.0 Stars(11)

Explore top flashcards

Flashcard140 terms
Studied by 7 people
Updated ... ago
5.0 Stars(1)
Flashcard124 terms
Studied by 27 people
Updated ... ago
5.0 Stars(1)
Flashcard39 terms
Studied by 44 people
Updated ... ago
5.0 Stars(2)
Flashcard39 terms
Studied by 2 people
Updated ... ago
5.0 Stars(1)
Flashcard46 terms
Studied by 18 people
Updated ... ago
5.0 Stars(1)
Flashcard70 terms
Studied by 3 people
Updated ... ago
5.0 Stars(1)
Flashcard64 terms
Studied by 10 people
Updated ... ago
5.0 Stars(1)
Flashcard41 terms
Studied by 82 people
Updated ... ago
5.0 Stars(1)