Thermo Final Exam Short Answer Questions

Question 1

The resultant pressure force acting on a body completely or partially submerged in a liquid is the:

Answer 1

Buoyant Force

Question 2

A system consisting of liquid water and ice undergoes a process. At the end of the process, the ice has melted and the system contains only liquid water. Can the system be considered a pure substance during the process? Explain.

Answer 2

The system is a pure substance. Although the phases change, the system remains of fixed chemical composition and is chemically homogenous.

Question 3

What is the difference between the triple point and the triple line?

Answer 3

The tripe line of the three-dimensional p-v-T surface projects onto a point on the phase diagram. This is called the triple point.

Question 4

What method do we use to retrieve the unknown specific volume between two temperature points on a T-v diagram?

Answer 4

Linear interpolation

Question 5

If a substance undergoes a constant - pressure expansion at a pressure higher than its critical pressure, can it undergo a phase change? If so, what phases are involved?

Answer 5

Yes. Solid and Liquid Phases.

Question 6

What is the state principle for simple systems?

Answer 6

For a simple compressible system, specification of the values for any two independent intensive thermodynamic properties will fix the values of all other intensive thermodynamic properties.

Question 7

Provide any two examples of a phase change.

Answer 7

Evaporation and Condensation

Question 8

The time rate of mass flow per unit area is called:

Answer 8

Mass Flux

Question 9

_____ - ____ means all properties are unchanging in time.

Answer 9

Steady-State

Question 10

A system consists of liquid water in equilibrium with a gaseous mixture of air and water vapor. How many phases are present? Does the system consist of a pure substance? Explain.

Answer 10

Two phases are present (liquid and gas). Not a pure substance because chemical composition is different in each phase.

Question 11

A device in which power is developed as a result of a gas or liquid passing through a set of blades attached to a shaft free to rotate.

Answer 11

Turbine

Question 12

A device in which work is done on a gas to increase the pressure and/or elevation.

Answer 12

Compressor

Question 13

A device in which work is done on a liquid to increase the pressure and/or elevation.

Answer 13

Pump

Question 14

A flow passage of varying cross-sectional area in which the velocity of a gas or liquid increases in the direction of flow.

Answer 14

Nozzle

Question 15

A flow passage of varying cross-sectional area in which the velocity of a gas or liquid decreases in direction of flow.

Answer 15

Diffuser

Question 16

A device where two moving fluid streams exchange heat without mixing.

Answer 16

Tube-within-a-tube counterflow heat exchanger

Question 17

A flow restricting device that causes a significant pressure drop in the fluid.

Answer 17

Throttling Device

Question 18

Which statement denies the transfer of heat from cooler to hotter body?

Answer 18

The Clausius Statement

Question 19

The process for which there are no irreversibilities within the system is called:

Answer 19

An internally reversible process.

Question 20

An ideal gas in a piston-cylinder assembly expands isothermally, doing work and receiving an equivalent amount of energy by heat transfer from the surrounding atmosphere. Is this process of the gas in violation of the Kelvin-Planck statement of the 2nd law? Explain.

Answer 20

No, the gas does not undergo a thermodynamic cycle.

Question 21

The h-s diagram is commonly known as the:

Answer 21

Mollier Diagram

Question 22

In a closed system when s1 = s2, the process must be ____ reversible.

Answer 22

Internally

Question 23

A closed system undergoes a process for which S2 = S1. Must the process be internally reversible? Explain.

Answer 23

The process does not have to be internally reversible, there could be entropy transfer by heat.

Question 24

With ___, steam expands through a first - stage turbine to an intermediate pressure, returns through a steam generator, and then expands through a second-stage turbine to the condenser pressure.

Answer 24

Reheat

Question 25

Among the principal irreversibilities of a gas turbine power plant, the most significant source of irreversibility by far is ______.

Answer 25

Combustion

Question 26

The Carnot refrigeration cycle consists of internally reversible processes and areas on a _____ can be interpreted as heat transfers.

Answer 26

T-s diagram

Question 27

Why is wet compression avoided within refrigeration cycle compression?

Answer 27

The presence of liquid droplets in flowing liquid vapor mixture can damage the compressor.

Question 28

The refrigerant temperature in the condenser is several degrees ____ the temperature of the warm region, TH.

Answer 28

Above

Question 29

A gas refrigeration application is often used to cool the interior cabin of a(n) ___.

Answer 29

Aircraft