FINAL PWEN ABSA PRACTICE EXAM FRIDAY 21 APRIL Flashcards
The term prime movers refers to
A single device that either by itself or as part of a system converts a natural source of energy into motion
Dry cooling towers
Pass the cooling water through a closed circuit of finned tubes
Impulse turbines
- Have a velocity increase through the nozzles
- Blades have the angle of inlet the same as the outlet
- Could have more than one set of blades
- May not require a trust bearing
In a reaction steam turbine
Expansion takes place in the fixed and moving blades
The rate of heat transfer in any cooling tower system depends on the:
Relative velocity of both air and water during contact
Length of contact time between the air and water
Difference between the inlet water T and the inlet air wet bulb T
Some of the characteristics that make the gas turbine a better choice over other prime movers are:
Low maintenance
Minimum cooling water
Rapid start-up and loading
The air side of a gas turbine regenerator is located:
Downstream of the compressor
In a compression ignition engine, the fuel is ignited by:
The compressed air temperature
A fuel injector is used to _____ the fuel in an engine:
Ignite
Cavitation of a pump refers to, when the:
Pump is filled with vapour
The capacity of a centrifugal pump should only be reduced by:
throttling the discharge valve
Which type of pump produces the greatest suction?
Positive displacement
Wear rings:
Are used on impellers
Are used on the casing
Reduce the maintenance costs of the pump
An air compressor may be automatically started and stopped by a pressure switch, which is usually found connected to the:
Receiver
Compressor unloaders:
Keep the suction valve open
Grease
Can be used under condition where oil may leak away and leave the bearing dry
Is less likely to drip or splash from bearings and therefore finds wide application in the textile and food industries
Serves to seal out dirt and water from bearings
Gives the working surface a permanent protective coating to prevent rusting during idle periods
The most common cause of lubrication problems in anti-friction bearings is:
over-lubrication
Trust bearing
Are used on reaction turbines
Prevent the turbine rotor from moving axially
Are lubricated with the same oil as the main bearings
In an equivalent circuit developed from a multi-resistor series circuit
The sum of voltage drops across the original resistances will be equal to the voltage drop of the equivalent circuit
Current flow direction and intensity will:
Affect magnetic field direction and intensity
Faraday discovered:
That a conductor will have a voltage induced if it cuts magnetic flux
Voltmeters are connected with the negative or black lead connected to the:
Negative side of the circuit
A kilowatt-hour meter has a small motor which:
Ha s a speed proportional to the power consumption
The rotating field of an alternator is obtained by exciting the windings on the rotor with
DC Power
When synchronizing an alternator; voltage, phase and frequency must all be the same as well as the:
Phase sequence
When magnetic flux produced by one coil induces an EMF in a second coil, it is called:
Mutual inductance
When AC action causes a counter current in a coil, it is termed:
Self inductance
An electrical distribution system is composed of service, feeders and:
branch circuits
A sensing element receives its signal from the:
Controlled variable
The purpose of a spiral or a helix Bourdon tube is to:
To provide a greater degree of rotation
Relative to flow, velocity is kinetic energy and when velocity increases, the:
Potential energy in the form of pressure will decrease
The common standard control modes for a plant control system are:
Derivative, proportional and integral
The most reliable method of checking or testing a low water fuel cutoff is to:
Lower the water in the boiler to the level where the burner should cut out
Safety devices and interlocks on boilers, when activated, shut off the:
Fuel
Digital output is put through a/an _____ before an analog control can react to the signal
Analog converter
The steam and water spaces of a cast iron sectional boiler are connected by:
Push nipples
Cast iron boiler sections maximize heat transfer by:
Exposing as large a surface as possible to the hot gases