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Presentation on theme: "Cycles"— Presentation transcript:
Slide1
Cycles
Contributions by:
John L. Falconer & Will Medlin
Department of Chemical and Biological Engineering
University of Colorado
Boulder, CO 80309-0424
Supported by the National Science Foundation
Slide2
Consider the best possible heat engine working in air at 25°C. The engine continuously converts heat from a source at 300°C to work, and heat is continuously transferred into the engine at a rate of 100 kJ/s. The maximum possible rate at which the engine can continuously produce work is ___________ 100 kJ/s.
greater than
equal to
almost
significantly less than
Slide3
For a Carnot heat engine, which statement must be incorrect?
|Q
c
| > |W|
|Q
H
| < |W|
|Q
H
| > |Q
C
|
Slide4
A Carnot heat engine is run in reverse so for every 100 kJ of electrical work added to the pump, 700 kJ of heat is added to the building. Is this consistent with the 1st and 2nd laws?
Yes
No
Cannot be determined
Slide5
Which diagram corresponds to a Carnot engine in which both adiabatic steps in the cycle are irreversible?
T
S
1
2
4
3
A
B
T
S
1
2
4
3
D
S
T
1
2
4
3
T
S
1
2
4
3
C
Slide6
Which diagram corresponds to a Carnot heat pump in which both adiabatic steps in the cycle are irreversible?
T
S
1
4
2
3
T
S
1
4
2
3
T
S
1
4
2
3
T
S
1
4
4
3
A
C
B
D
Slide7
Which diagram represents a Rankine cycle?
P
H
P
P
P
H
H
H
A
B
C
D
Slide8
Which diagram represents a Rankine cycle?
P
H
P
P
P
H
P
H
H
H
A
B
C
D
E
Slide9
Which diagrams are not possible for a vapor compression refrigeration cycle using a throttle valve?
2 & 51 & 42, 3, & 41, 2, 4, & 51, 4, & 5
T
T
S
T
S
S
S
S
#1
#2
#3
#4
#5
T
T
Slide10
Which diagrams do not represent a vapor compression cycle? The compressor is adiabatic, the expansion valve is a throttle process, the evaporator and condenser are each at constant pressure.
11 & 222 & 33
P
H
P
P
H
H
#1
#2
#3
Slide11
Which diagrams do not represent a vapor compression cycle? The compressor is adiabatic, the expansion valve is a throttle process, the evaporator and condenser are each at constant pressure.
11 & 21 & 32 & 33
P
H
P
P
H
H
#1
#2
#3
Slide12
Indicate, in the correct order, which P-H diagram represents a vapor compression cycle and which represents a Rankine power cycle.
1& 22 & 33 & 44 & 21 & 3
P
P
H
H
#3
#4
P
P
H
H
#1
#2
Slide13
A
B
C
D
Pressure
Enthalpy
(kJ/kg
)
Which line is most likely to represent a reversible turbine in a
Rankine
cycle?
Slide14
A
B
C
D
Pressure
Enthalpy
(kJ/kg
)
Which line is most likely to represent a liquid pump?
Slide15
A well-insulated water heater heats water from 10°C to 50°C. The efficiency of the process is _______________ .
much greater than 1
much less than 1
almost equal to 1
not possible to tell
Slide16
Which will require more work to compress from 1 atm to 100 atm?
Liquid
Gas
Solid
Slide17
Liquid water at 1.5 MPa and 180°C expands continuously through a throttling valve to 100 kPa. What can you definitely say about this system?
All the liquid evaporates
Some of the liquid evaporates
The temperature increases
The temperature does not change
Slide18
Liquid water at 1.5 MPa and 180°C expands continuously through a throttling valve to 100 kPa. What can you definitely say about this system?
All the liquid evaporates
The temperature increases
The temperature decreases
The temperature does not change
Slide19
1,000 J/s electrical energy is supplied to a heat pump for a house. Which is the most likely amount of heat that is provided to the house?
35,000
J/s
3,000 J/s
1,000 J/s
400 J/s
Slide20
Rank the following types of energy in terms of quality:1) hot combustion gas 2) hot water3) electricity 4) chemical energy
4 > 3 > 1 > 2
3 > 4 > 1 > 2
3 > 1 > 4 > 2
4 > 1 > 3 > 2
4 > 3 > 2 >
1
Slide21
The quality of steam from an irreversible turbine, compared to a reversible turbine, at the same final pressure is _______.
higher
lower
the same
Slide22
Liquid water at 10°C flows into an insulated tank where an electric heating element heats it to its exit temperature of 50°C. The efficiency of this process is ____________ 100%.
much greater than
about equal to
much less than
Slide23
Which cannot be done continuously?
Convert 100 kJ work to 100 kJ heat
Convert 100 kJ electricity to 200 kJ heat
Convert 100 kJ heat to 100 kJ work
Both A and B
Slide24
Which statement is incorrect?
Work
can be continuously converted to heat
with efficiency close to 100%
Heat
can be continuously converted to work
with efficiency close to 80%
Electricity
can be continuously converted to
work with efficiency greater than 50%
Electricity
can be converted to heat with
efficiency close to 100%
Slide25
Suppose both adiabatic steps in a Carnot cycle are irreversible. Which is the correct statement about the entropy change of the Carnot engine?
