Fluid Machines Flashcards
What is a pump and compressor?
A machine that converts mechanical energy into fluid energy.
What can be assumed from inspection of a pump or compressor?
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.
What is hydraulic power or pump power?
The net power transferred to the fluid by the pump.
How is the energy from the pump to the fluid manifested?
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.
What is the work energy principle?
The energy added is equal to the work done on the fluid.
What losses does the pump efficiency account for?
Power lost from the friction between the fluid and the pump and friction in the pump bearings.
What is purchased or electrical power?
The electrical power drawn from the power line.
What losses does the motor efficiency account for?
Power losses due to the frictional losses in the motor bearings, air wind age, and electrical heating.
What is brake power?
the output power.
What is the total pump efficiency equal to?
The product of the motor and pump efficiencies.
What is the isentropic efficiency of a compressor?
The ratio of the ideal energy input to actual energy input.
What are turbines?
Are pumps operating in reverse. Converts fluid energy into mechanical energy.
What can be assumed from inspection of a turbine?
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.
What is the isentropic efficiency of a turbine?
The ratio of the actual energy output to ideal energy output.
What is cavitation?
A spontaneous vaporization of the fluid inside the pump, resulting in a degradation of pump performance.
What are manifestations of cavitation?
Noise, vibration, impeller pitting and structural damage to the pump casing.
When does cavitation occur in a pump?
Wherever the fluid pressure is less than the vapor pressure.
What causes cavitation in terms of head?
When the available head is less than the required head for satisfactory operation.
What is the net positive suction head required?
The minimum fluid energy required at the pump inlet for satisfactory operation.
What is the net positive suction head available?
The actual total fluid energy at the pump inlet.
What are dynamically similar pumps?
The performance of one pump can be used to predict the performance of another pump.
When are the similarity laws used?
To scale the performance between dynamically similar pumps.
What do the similarity laws assume between dynamically similar pumps?
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.
How do axial fans develop static pressure?
Fans that develop static pressure by changing the airflow velocity.
Under what conditions are axial fans used?
When it is necessary to move large quantities of air against low static pressures.
What are the pros and cons of axial fans to centrifugal fans?
They are more compact and less expensive. However, they run faster than centrifugals, draw more power, are less efficient, and are noisier.
Under what conditions are centrifugal fans used?
When moving air at less than 500 meters cubed per second and pressures less than 15 kpa.
How do centrifugal fans develop static pressure?
Fans that develop static pressure by imparting a centrifugal force on the rotating air.
How does the curvature of the blade effect the a centrifugal fan?
Kinetic energy can be made greater or less than the tangential velocity of the impeller.
Under what conditions are forward curved centrifugals used?
They are useful in high temperature applications where stress due to rotation is a factor.
When cant forward curved centrifugal fans be used?
When the air contains particles or contaminants.
What are the radial fans characteristics?
Are fans with low volume, high pressure, high noise, high temperature, and low efficiency.
What shape are the radial fans blades?
They are fans with blades that are neither forward of backward inclined.
What are the backward centrifugals fans characteristics?
They are quiet, medium to high volume and pressure, and high efficiency units.
What are the clean air temperature and pressure range for backward curved centrifugals?
The temperatures below 540 degrees Celcius and up to pressures of 10 kPa.
