Exam (elaborations)
Prime Movers and Engines/Pumps And Compressors/Heating Boilers – Q&A
Prime Movers and Engines/Pumps And Compressors/Heating Boilers – Q&A
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Prime Movers and Engines/Pumps AndCompressors/Heating Boilers – Q&A
What kinds of factors would decide what type of energy transfer system to
use? ✔️Ans - - Type/Cost of fuel
- Transmission Distance
- Equipment Cost
- Manpower
- Repair Costs
A heat engine is refers to one specific device. True or False? ✔️Ans - False. A
heat engine can be a single device, a system or a cycle of operations.
What is the specific name for the cycle of operations in a gas powered engine?
✔️Ans - The Otto Cycle.
Could an entire steam plant be considered a Heat Engine? ✔️Ans - Yes. It
would have numerous devices, the working fluid is water and steam and the
process is called the Rankine cycle.
What is a Prime Mover? ✔️Ans - A single device, either by itself or as part of
an overall heat engine, converts a natural source of energy into natural
motion.
A steam turbine is a heat engine but not a prime mover. True or False?
✔️Ans - False, it is a prime mover but not by itself a heat engine.
1) Examples of heat engines?
2) Examples of prime movers? ✔️Ans - a) compression ignition engines, gas
turbines, jet engines, steam plants producing power.
b) Steam turbines, steam engines, hydraulic turbines, wind turbines.
Electric motors are not a prime mover. True or False? ✔️Ans - True.
Potential energy sources used in large scale production of power? ✔️Ans -
Solid, liquid and gaseous carbon-based fuels, waterpower and nuclear energy.
,Why are steam plants so widely used? ✔️Ans - - Burn solid fuels such as
coal and wood
- Highest overall efficiency
- Internal combustion engines limited to liquid or gaseous fuels
A few specialized applications steam engines still have? ✔️Ans - - Slow
rotational speed is required without reduction gearing
- Reversal of rotational direction without gearing is required
- Driving reciprocating pumps
- Restored steam engines
General description of a basic Steam Engine? ✔️Ans - Single cylinder,
double acting, vertical engine with a D slide valve and a throttling governor.
Purpose of the Slide valve? ✔️Ans - Controls admission and exhaust to and
from the engine cylinder.
Composition of a valve gear? ✔️Ans - Eccentric, Eccentric rod and Valve
Rod. Slide valve has a reciprocating motion timed to match the motion of the
piston imparted by the valve gear.
How does the steam act on the piston? ✔️Ans - Acts above to give a
downward thrust and above to give an upward thrust.
Why is steam supply cut off part way through a stroke? ✔️Ans - It is cut off
1/4-1/3 of the way through its stroke because the steam is expanding
throughout the stroke. The Slide valve then opens to exhaust steam out of the
piston.
Benefit of using the "expansive" approach to operation? ✔️Ans - More
economical. Very few steam engines continue steam admission throughout the
whole stroke.
2 critical actions that take place in the steam engine? ✔️Ans - - Up and down
action of the piston in the cylinder (which then turns the crankshaft)
- Slide action of the D valve - lets in steam and exhausts steam and is
controlled by the movement of the crankshaft
,Describe the sheave of Eccentric. ✔️Ans - - Made in halves secured bolts and
split cotter pins
- Band surrounding the sheave is called the strap.
Which device converts reciprocating motion into rotary motion between the
crankshaft and piston? ✔️Ans - The crank pin shrunk into the crank disc
into which the end of the crankshaft is also shrunk.
What is the purpose of the Crosshead? ✔️Ans - It makes the angular push or
pull of the connecting rod against the piston rod during the greater part of the
revolution when these rods are not in line.
What prevents steam from leaking past the piston rod/valve rod? ✔️Ans -
Packing stuffed in the Packing box.
Drain cocks? ✔️Ans - Used to drain any condensate formed at the bottom of
the piston.
There is greater force at the end of a stroke V.S. the beginning of a stroke. True
or False? ✔️Ans - False, there is always greater force at the beginning of the
stroke.
Flywheel? ✔️Ans - Fitted to dampen or even out the changes of speed
caused by varying steam pressure. The flywheel also carries the engine over
dead centre when the pistons aren't moving.
How does a flywheel always maintain dead centre? ✔️Ans - It takes a
considerable amount of force to start it in motion or to spot it.
Steps to Starting a steam engine: ✔️Ans - 1) No tools laying around, parts
are clear for movement
2) Steam chest and Cylinder Drains are open.
3) Open separator drain on steam line to empty water
4) If drain valve not draining, open stop valve to let live steam enter
5) Dont cause water hammer
Things to look for in a running steam engine? ✔️Ans - - Lubrication
- Bearing Operation
- Running temperature
, - Strange noises
Steam flow is regulated to control engine speed by what? ✔️Ans - A
Throttling Valve
Advantages of a Steam Turbine over a steam engine? ✔️Ans - - Greater
thermal efficiency
- Compact in size
- Easily coupled with an electrical generator
- Lubrication is easier
- Oil free condensate (recycle)
- Bearings are located out of the steam zone and do not need to withstand high
pressures and temperatures.
Impulse turbine? ✔️Ans - Entire steam pressure drop takes place in the
stationary nozzles
Reaction turbine? ✔️Ans - Steam pressure drops passing through the
moving blades as well as the stationary nozzles or blades
Stationary passages? ✔️Ans - - Lower pressure, higher speed
- One or more stationary nozzles
What is the name of the stationary passage of a reaction turbine? ✔️Ans -
Fixed Blade.
Where is the thrust imparted by the steam derive from on an impulse blade?
✔️Ans - From the change in momentum, or impulse, of the steam as it changes
direction to follow the shape of the blades.
What forms the rotor flow passage? ✔️Ans - Blades and buckets.
Impulse blades? ✔️Ans - - The space between the blades doesn't allow any
pressure drop between the spaces
- Thrust comes from change in momentum
Reaction blades? ✔️Ans - - Allow a steam pressure drop between the blades
resulting in an increase in steam speed creating a back thrust on the blades
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