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Flashcards in Exam 2 Deck (69):
1

The equation (velocity*cross sectional area)/specific volume is used to compute?

mass flow

2

which of the following is NOT a valid unit for measuring pressure:
a.) psi
b.) mm Hg
c.) kPa
d.) in H2O
e.) none of these

none of these

3

the SI unit for specific heat is

kJ/(kg-K)

4

an English unit for power is

Btu/hr

5

(TURE OR FALSE) a cycle is part of a process

false

6

(TURE OR FALSE) an isentropic process is adiabatic

false

7

what is the difference between mechanical efficiency (nm) and thermal efficiency(nt)?

nm applies to processes and nt applies to cycles
nm applies to first law of thermodynamics and nt applies to 2nd law or thermodynamics

8

what is the functional difference between a pump and a compressor?
a.) no difference, same as 1st law equation for both devices
b.) pump handles gases, compressor handles liquids
c.) pump handles small volumetric flow, compressor handles large volumetric flow
d.) pump handles large mass flow, compressor handles small mass flow
e.) none of these

none of these

9

the term isobaric means

constant pressure

10

use the first law of thermodynamics to derive a simplified equation for a throttle that explains its performance based on inlet (1) and outlet (2) conditions.

0 = h2 - h1

11

use the first law of thermodynamics to derive a simplified equation for a nozzle that explains its performance based on inlet (1) and outlet (2) conditions

0 = 1/2(v2^2 - v1^2) + (h2 - h1)

12

an engine produces 8.0 kW of power with a thermal efficiency of 20%. What is the rate of heat rejection for this cycle?

nth = W/Qh
0.2 = 8/Qh
Qh = 40
Ql/Qh = 0.8
Ql/40 = 0.8
Ql = 0.8 (40)
Ql = 32

13

Even though the Carnot Cycle has never been built, it is still useful because it

defines peak performance.

14

A Carnot heat pump supplies warm air to a building at 100 degrees F. What is the coefficient of Performance when to cold outside air is -10 degrees F?

COP = Th/(Th-Tl)
COP = 560/(100-(-10))
COP = 560/110
COP = 5.1

15

A turbine for an ideal Rankine Cycle power plant decreases the pressure of the water but does not change its

entropy

16

what are the English units for "k" in the conduction equation Q = -k*A(delta T/delta x)

Btu - in/(hr - ft^2 - degrees F)

17

what new design information do heat transfer equations provide Thermodynamics equations?
a.) temperature
b.) pressure
c.) flow
d.) solid, liquid, gas
e.) none of these

none of these, area and size

18

fill in the blank: ___ & ___ are used to estimate Nusselt #, which is then used to estimate the convection heat transfer coefficient

Reynolds # & Prandtl #

19

An empirical equation is?

determined be experiments

20

The inverse of specific volume (1/v) is?

density

21

The magnehelic pressure gage used in the hair dryer experiment measured velocity pressure in units of?

fpm

22

the flow of air in a duct would most likely be expressed in

cfm

23

the power supplied to an electric motor would likely be expressed in

kW

24

which of the following is energy (not power)?
a.) hp
b.) Btu/hr
c.) therm
d.) kW
e.) none of these

therm

25

The English unit for specific heat (c) is?

Btu/(lbm-R)

26

m*c*delta T has units of

energy

27

Enthalpy is a derived property that combines

internal and flow energy

28

(TRUE OR FALSE) hfg quantifies latent energy

true

29

(TRUE OR FALSE) hf > hg for a fluid

false

30

An open system has

mass flow

31

sensible energy is "heat transfer by virtue of ____ change"

temperature

32

A 1st law analysis of a diffuser shows that it converts

pressure to kinetic energy

33

The term isentropic means
a.) constant volume
b.) constant pressure
c.) constant temperature
d.) constant mass
e.) none of these

none of these

34

use the first law of thermodynamics to derive a simplified equation for a turbine that explains its performance based on inlet (1) and outlet (2) conditions

w=h2-h1

35

what are two modes of operation for a heat pump?

heating or work

36

An engine uses 80 kW of heat to deliver 20 kW of useful work. How much heat is rejected to surroundings?

60

37

The ____ Cycle represents perfection in terms of heat engine performance.

Carnot

38

A Carnot heat pump supplies warm air to a building at 100 degrees F. What is the Coefficient of Performance when the cold outside air is 20 degrees F?

7

39

How much electricity is needed to operate a heat pump with a COP of 3 that provides 3kW of useful cooling?

1kW

40

A boiler for an ideal Rankine Cycle power plant increases the temperature of the water but does not change its ____.

pressure

41

The energy transfer to water in the boiler for a power plant is?

sensible and latent

42

Which device in a power plant transfers the least energy?
a.) pump
b.) turbine
c.) boiler
d.) condenser
e.) none of these

pump

43

Air removing heat form a light bulb is an example of ____ heat transfer

convection

44

Heat moving through a solid object is an example of?

conduction

45

Thermal efficiency of a heat engine

nth = output/input
nth = Wnet/Qh
nth = 1-Ql/Qh

46

Coefficient of Performance

COP = output/input
COP = Qh/(Qh-Ql)

47

Carnot Heat engine

nth = output/input
nth = Wnet/Qh
nth = 1-Tl/Th

48

What is the difference between mechanical and thermal efficiency?

Thermal: amount of work that can be obtained
Mechanical: how efficiently the engine converts from one form of energy to another

49

What is 2nd Law efficiency?

the efficiency of a process taking into account the 2nd law of thermodynamics

50

What is entropy?

property based on heat transfer and temperature
defined in terms of dS = delta*Q/T
also quantifies magnitude of irreversibility in a process

51

causes of entropy change

heat transfer, irreversibilities, mass transfer

52

Rankine cycle

the ideal steam power plant cycle consisting of 4 processes: boiler, turbine, condenser, and feedwater pump

53

Thermodynamics vs, Heat Transfer

how much vs. how big

54

types of heat transfer

conduction, convection, radiation

55

conduction

heat transfer due to particle interaction with a substance or between two similar substances
Qcond = -kA(delta T/delta x)

56

convection

heat transfer between a surface and a moving fluid
Qconv= hA(Ts-Tinfinity)

57

radiation

transfer by electromagnetic wave
Qrad = epsilon*sigma*A(Ts^4-Tsurr^4)

58

heat transfer coefficient "h"

measure of capability for heat flow from surface to fluid
as h increases, Q increases
varies with type of fluid, flow conditions and surface properties

59

Which line on the T-S graph shows a process where superheated steam enters a condenser at point 1 and exits as a saturate mixture at point 2? (see notecard 1)

c

60

which line on the T-S graph shows a process where a saturated vapor enters a condenser at point 1 and exits as a subcooled liquid at point 2? (see notecard 1)

b

61

(TRUE OR FALSE) from looking at the heat engine sketch, W = Qh-Ql. (see notecard 2)

true

62

which of the sketches correctly summarizes a heat engine? (see notecard 3)

c

63

which of the sketches correctly summarizes a heat pump? (see notecard 3)

d

64

Which of lines on the T-S graph represent an isobaric process? (see notecard 4)

B and D

65

Which of the lines on the T-S graph represent the turbine in a power plant? (see notecard 4)

c

66

Name pump, boiler, turbine and condenser in the diagram. (see notecard 4)

a: pump
b: condenser
c: turbine
d: boiler

67

isobaric

T does not change, entropy does

68

power plant schematic

(see notecard 5)

69

name each of the 3 states (see notecard 6)

1: compressed liquid
2: saturated liquid-vapor mixture
3: superheated vapor