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Fluid Mechanics > Fluid Machines > Flashcards

Fluid Machines Flashcards

1
Q

What is a pump and compressor?

A

A machine that converts mechanical energy into fluid energy.

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2
Q

What can be assumed from inspection of a pump or compressor?

A

It is assumed to be adiabatic and if the inlet and outlet are the same size and at the same elevation, the kinetic and potential energies can be neglected.

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3
Q

What is hydraulic power or pump power?

A

The net power transferred to the fluid by the pump.

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4
Q

How is the energy from the pump to the fluid manifested?

A

It is manifested primarily by an increase in pressure, and to much lesser degree, changes in velocity and, sometimes, elevation across the pump inlet and outlet.

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5
Q

What is the work energy principle?

A

The energy added is equal to the work done on the fluid.

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6
Q

What losses does the pump efficiency account for?

A

Power lost from the friction between the fluid and the pump and friction in the pump bearings.

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7
Q

What is purchased or electrical power?

A

The electrical power drawn from the power line.

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8
Q

What losses does the motor efficiency account for?

A

Power losses due to the frictional losses in the motor bearings, air wind age, and electrical heating.

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9
Q

What is brake power?

A

the output power.

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10
Q

What is the total pump efficiency equal to?

A

The product of the motor and pump efficiencies.

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11
Q

What is the isentropic efficiency of a compressor?

A

The ratio of the ideal energy input to actual energy input.

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12
Q

What are turbines?

A

Are pumps operating in reverse. Converts fluid energy into mechanical energy.

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13
Q

What can be assumed from inspection of a turbine?

A

It is assumed to be adiabatic and if the inlet and outlet are the same size and at the same elevation, the kinetic and potential energies can be neglected.

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14
Q

What is the isentropic efficiency of a turbine?

A

The ratio of the actual energy output to ideal energy output.

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15
Q

What is cavitation?

A

A spontaneous vaporization of the fluid inside the pump, resulting in a degradation of pump performance.

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16
Q

What are manifestations of cavitation?

A

Noise, vibration, impeller pitting and structural damage to the pump casing.

17
Q

When does cavitation occur in a pump?

A

Wherever the fluid pressure is less than the vapor pressure.

18
Q

What causes cavitation in terms of head?

A

When the available head is less than the required head for satisfactory operation.

19
Q

What is the net positive suction head required?

A

The minimum fluid energy required at the pump inlet for satisfactory operation.

20
Q

What is the net positive suction head available?

A

The actual total fluid energy at the pump inlet.

21
Q

What are dynamically similar pumps?

A

The performance of one pump can be used to predict the performance of another pump.

22
Q

When are the similarity laws used?

A

To scale the performance between dynamically similar pumps.

23
Q

What do the similarity laws assume between dynamically similar pumps?

A

They assume that both pumps operate in the turbulent region, have the same pump efficiency and operate at the same percentage of wide open flow.

24
Q

How do axial fans develop static pressure?

A

Fans that develop static pressure by changing the airflow velocity.

25
Q

Under what conditions are axial fans used?

A

When it is necessary to move large quantities of air against low static pressures.

26
Q

What are the pros and cons of axial fans to centrifugal fans?

A

They are more compact and less expensive. However, they run faster than centrifugals, draw more power, are less efficient, and are noisier.

27
Q

Under what conditions are centrifugal fans used?

A

When moving air at less than 500 meters cubed per second and pressures less than 15 kpa.

28
Q

How do centrifugal fans develop static pressure?

A

Fans that develop static pressure by imparting a centrifugal force on the rotating air.

29
Q

How does the curvature of the blade effect the a centrifugal fan?

A

Kinetic energy can be made greater or less than the tangential velocity of the impeller.

30
Q

Under what conditions are forward curved centrifugals used?

A

They are useful in high temperature applications where stress due to rotation is a factor.

31
Q

When cant forward curved centrifugal fans be used?

A

When the air contains particles or contaminants.

32
Q

What are the radial fans characteristics?

A

Are fans with low volume, high pressure, high noise, high temperature, and low efficiency.

33
Q

What shape are the radial fans blades?

A

They are fans with blades that are neither forward of backward inclined.

34
Q

What are the backward centrifugals fans characteristics?

A

They are quiet, medium to high volume and pressure, and high efficiency units.

35
Q

What are the clean air temperature and pressure range for backward curved centrifugals?

A

The temperatures below 540 degrees Celcius and up to pressures of 10 kPa.

Fluid Mechanics (6 decks)

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