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# Cycles

## Cycles

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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

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

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?

ΔS

engine

> 0

ΔS

engine

= 0

ΔS

engine

< 0

None of the above