Chapter 5 Flashcards

1
Q

Conservation of Mass

A

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

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2
Q

Closed systems

A

The mass of the system remain constant during a process

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3
Q

Control volumes

A

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

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4
Q

The mass change due to energy change

A

Is negligible

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5
Q

The average speed through a cross section

A

Average velocity

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6
Q

Volume of fluid flowing through a cross section per unit time

A

Volume flow rate

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7
Q

The conservation of mass principle for a control volume

A

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

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8
Q

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

A

Does not change with time (Mcv = constant)

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

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9
Q

Single stream

A

Nozzles, diffusers, turbines, compressors, pumps

One inlet and one outlet

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10
Q

Steady flow of liquids - Incompressible flow

A

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

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11
Q

During a steady-flow process

A

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

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12
Q

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.

A

Flow work, flow energy

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13
Q

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

A

Steady-flow process

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14
Q

Steady flow process - control volume

A

Mass and energy remain constant

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15
Q

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

A

Remain constant (do not change with time)

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16
Q

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

A

Shaft work and electrical work

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17
Q

Nozzles and diffusers are commonly utilized in

A

Jet engines, rockets, spacecraft, garden hoses

18
Q

Nozzle

A

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

19
Q

Diffuser

A

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

20
Q

Cross-sectional area of a nozzle

A

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

21
Q

Nozzles and diffusers are shaped so that they cause…

A

Large changes in fluid velocities and thus kinetic energies

22
Q

Turbine

A

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

23
Q

As fluid passes through the turbine…

A

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

24
Q

Compressors, pumps, fans

A

Devices used to increase the pressure of a fluid

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

25
Fan
Increases the pressure of a gas slightly and is mainly used to mobilize a gas
26
Compressor
Capable of compressing the gas to very high pressures
27
Pumps
Work very much like compressors except that they handle liquids instead of gases
28
Throttling valves
Are any kind of flow-restricting devices that cause a significant pressure drop in the fluid Internal Energy + Flow Energy = Constant Enthalpy = Constant
29
What is the difference between a turbine and a throttling valve?
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
30
The temperature of an ideal gas during a throttling process
Does not change
31
In engineering applications, the section where the mixing process takes place is commonly referred to as a ____
Mixing chamber
32
Conservation of mass principle for a mixing chamber
Requires that the sum of the incoming mass flow rates equal the mass flow rate of the outgoing mixture
33
Heat exchangers
Devices where two moving fluid streams exchange heat without mixing
34
Flow through a pipe or a duct usually satisfies the ____
Steady-flow conditions
35
Processes that change within the control volume with time
Transient-flow processes, unsteady processes
36
Most unsteady-flow processes can be represented reasonably well by ____ process
Uniform-flow
37
Uniform-flow process
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
38
___ of a control volume may change during an unsteady-flow process
Shape and size
39
The energy equation of a uniform-flow system reduces to that of a _____ when all the inlets and exits are closed
Closed system
40
A uniform-flow system may involve...
Electrical, shaft, and boundary work all at once