Chapter 5

Question 1

Conservation of Mass

Answer 1

Mass, like energy, is a conserved property, and it cannot be created or destroyed during a process

Question 2

Closed systems

Answer 2

The mass of the system remain constant during a process

Question 3

Control volumes

Answer 3

Mass can cross the boundaries, and so we must keep tract of the amount of mass entering and leaving the control volume

Question 4

The mass change due to energy change

Answer 4

Is negligible

Question 5

The average speed through a cross section

Answer 5

Average velocity

Question 6

Volume of fluid flowing through a cross section per unit time

Answer 6

Volume flow rate

Question 7

The conservation of mass principle for a control volume

Answer 7

The net mass transfer to or from a control volume during a time interval (change in t) is equal to the net change (increase or decrease) in the total mass within the control volume during change in t

Question 8

During a steady flow process, the total amount of mass contained within a control volume

Answer 8

Does not change with time (Mcv = constant)

The total amount of mass entering a control volume equal the total amount of mass leaving it

Question 9

Single stream

Answer 9

Nozzles, diffusers, turbines, compressors, pumps

One inlet and one outlet

Question 10

Steady flow of liquids - Incompressible flow

Answer 10

The volume flow rates, as well as the mass flow rates, remain constant since liquids are essentially incompressible substances

Question 11

During a steady-flow process

Answer 11

Volume flow rates are not necessarily conserved although mass flow rates are

Question 12

The work (or energy) required to push the mass into or out of the control volume. This work is necessary for maintaining a continuous flow through a control volume.

Answer 12

Flow work, flow energy

Question 13

A process during which a fluid flows through a control volume steadily

Answer 13

Steady-flow process

Question 14

Steady flow process - control volume

Answer 14

Mass and energy remain constant

Question 15

Steady-flow process - fluid properties at an inlet or exit

Answer 15

Remain constant (do not change with time)

Question 16

Under steady operation, ____ are the only forms of work a simple compressible system may involve

Answer 16

Shaft work and electrical work

Question 17

Nozzles and diffusers are commonly utilized in

Answer 17

Jet engines, rockets, spacecraft, garden hoses

Question 18

Nozzle

Answer 18

Device that increase the velocity of a fluid at the expense of pressure

Question 19

Diffuser

Answer 19

Device that increase the pressure of a fluid by slowing it down

Question 20

Cross-sectional area of a nozzle

Answer 20

Decreases in the flow direction for subsonic flows and increases for supersonic flows. Opposite for diffusers

Question 21

Nozzles and diffusers are shaped so that they cause…

Answer 21

Large changes in fluid velocities and thus kinetic energies

Question 22

Turbine

Answer 22

Drives the electric generator in steam, gas, or hydroelectric power plants

Question 23

As fluid passes through the turbine…

Answer 23

Work is done against the blade, which are attached to the shaft. This, the shaft rotates, and the turbine produces work

Question 24

Compressors, pumps, fans

Answer 24

Devices used to increase the pressure of a fluid

Work is supplied to these devices from an external source through a rotating shaft

Question 25

Fan

Answer 25

Increases the pressure of a gas slightly and is mainly used to mobilize a gas

Question 26

Compressor

Answer 26

Capable of compressing the gas to very high pressures

Question 27

Pumps

Answer 27

Work very much like compressors except that they handle liquids instead of gases

Question 28

Throttling valves

Answer 28

Are any kind of flow-restricting devices that cause a significant pressure drop in the fluid

Internal Energy + Flow Energy = Constant

Enthalpy = Constant

Question 29

What is the difference between a turbine and a throttling valve?

Answer 29

The pressure drop in the fluid is often accompanied by a drop in temperature and for that reason throttling devices are commonly used in refrigeration and air-conditioning applications

Question 30

The temperature of an ideal gas during a throttling process

Answer 30

Does not change

Question 31

In engineering applications, the section where the mixing process takes place is commonly referred to as a ____

Answer 31

Mixing chamber

Question 32

Conservation of mass principle for a mixing chamber

Answer 32

Requires that the sum of the incoming mass flow rates equal the mass flow rate of the outgoing mixture

Question 33

Heat exchangers

Answer 33

Devices where two moving fluid streams exchange heat without mixing

Question 34

Flow through a pipe or a duct usually satisfies the ____

Answer 34

Steady-flow conditions

Question 35

Processes that change within the control volume with time

Answer 35

Transient-flow processes, unsteady processes

Question 36

Most unsteady-flow processes can be represented reasonably well by ____ process

Answer 36

Uniform-flow

Question 37

Uniform-flow process

Answer 37

The fluid flow at any inlet or exit is uniform and steady, and thus the fluid properties do not change with time or position over the cross section of an inlet or exit. If they do, they are averaged and treated as constants for the entire process

Question 38

___ of a control volume may change during an unsteady-flow process

Answer 38

Shape and size

Question 39

The energy equation of a uniform-flow system reduces to that of a _____ when all the inlets and exits are closed

Answer 39

Closed system

Question 40

A uniform-flow system may involve…

Answer 40

Electrical, shaft, and boundary work all at once