1.2.1 Sources of Power in the Farm Flashcards
Oldest sources of power in the farm
Human Power
While fire is considered the greatest discovery of man; the _____ is the considered the greatest invention of man.
wheel
Human Power-____ hp
Animal Power-____hp
Human Power - 0. 1hp
Animal Power- 1 hp
Animal Power:
low work capacity - this means more time spent for a single operation (_____ h/ha plowing once)
25-50 h/ha
Animal Power:
low work capacity - this means more time spent for a single operation (_____ h/ha plowing once)
25-50 h/ha
Animal Power:
more labor input and drudgery (a farmer walks with the carabao __ km/ha), and limited working period to avoid the intense heat of the sun
77 km/ha
Determine the time required and distance travelled in plowing a onehectare field using a 13-cm wide animal-drawn plow with a field efficiency of 70%. If the draft is 60 kg and the animal is travelling at 3 kph, what is the horsepower output of the animal?
Time to plow one hectare (hr/ha) — 36.63 h/ha
Distance travelled per hectare (km) — 109.89 km
Horsepower output of animal (hp) — 0.66 hp
used to convert electrical energy into mechanical energy
Electric motor
Energy conversion efficiencies of major farm power units:
POWER UNIT ENERGY CONVERSION EFFICIENCY
Electric motor _______
Gasoline engine _______
Diesel engine _______
POWER UNIT ENERGY CONVERSION EFFICIENCY (%)
Electric motor 50-99
Gasoline engine 25
Diesel engine 40
commonly used as prime movers for stationary and indoor equipment such as those used for processing of farm products and by-products
Electric Motors
Electric motors :
available in fractional hp sizes (__, __, __Hp) and low integral hp sizes (__, __, ___, __, __ Hp)
fractional hp sizes (1/4, ½, ¾ Hp)
low integral hp sizes (1, 1 ½, 2, 2 ½, 3 Hp)
2 Types Electric Motors
AC and DC Motors
Type of motor which current is sent into the stator winding which is placed in a stationary laminated
iron core; the rotating element may or may not be a set of magnet poles.
AC motor
Type of motor which current is sent into the armature winding, which is placed in-between a set
of radially supported magnet poles.
Direct current (DC) motor
5ype of motor which is small series motors up to 3.73 kW rating which are commonly designed
to operate on either direct current or alternating current.
Universal motor
Direct-current motors main components:
1.
2.
3.
Field pole, Armature (rotor), and Commutator
Direct-current motors main components:
1.
2.
3.
Field pole, Armature (rotor), and Commutator
—interaction of two magnetic fields causes the rotation in a DC motor.
—north and south poles that are stationary and an armature (rotor) that turns on bearings in the space between the field poles.
Field pole
—becomes an electromagnet when current goes through it.
— linked to a drive shaft in order to drive the load.
— it rotates in the magnetic field established by the poles, until the north and south poles of the magnets change location with respect to the armature.
— the current is reversed to switch the south and north poles of the armature. Thus rotation is achieved
Armature (rotor)
is found only in DC motors. Its purpose is to overturn the direction of the electric current in the armature. It also aids in the transmission of current between the armature and the power source.
Commutator
—use direct-unidirectional current.
—commonly used in special applications where high torque starting or smooth acceleration over a broad speed range is required.
Direct-current motors
—use an electrical current, which reverses its direction at regular intervals.
— majority of electrical motors used in homes and on farms are alternating current motors.
—difficult to control the speed; can be equipped with variable frequency drives
Alternating -current motors
Electric motor two major parts:
stator and rotor
—runs at constant speed requires direct current (DC) for excitation
—low starting torque.
—Applications: low load requirement such as air compressors, frequency changes and motor generators.
Example : clocks and timers
Synchronous motor
A type of DC motor, in which the field winding is connected in parallel with the armature.
NOTE: used in constant speed application.
Shunt-wound motor
A type of DC motor, in which the field winding is connected in series with the armature.
NOTE: The series motor is used in applications where a high starting torque is required.
Series-wound motor
A type of DC motor, which has a series-field and shunt-field winding.
NOTE: the drop of the speed-torque characteristics may be adjusted to
suit the load.
Compound-wound motor
A type of AC motor capable of raising the power factor of systems having large induction-
motor loads.
Synchronous
A type of AC motor, wherein secondary windings are wound with discrete conductors with
the same number of poles as the primary winding on the stator.
Wound-rotor
A type of AC motor wherein the rotor or secondary winding consists merely of 28 identical
copper or cast-aluminum bars solidly connected to conducting end wings on each end, thus
forming a “squirrel-cage” structure.
Squirrel-cage
Classification of electric motors based on electrical service required:
Single-phase alternating current (__ hp)
Three-phase alternating current (__ hp)
Single-phase alternating current (< 5 hp)
Three-phase alternating current (> 5 hp)
Calculate the maximum locked-rotor current (starting current) for a ½-hp, 220-volt motor with an H motor code.
A=16.14 amp.
refers to how frequently the motor is started and for how long it will run each time it is started.
Motor duty
is the type of service in which the motor is operated for more than 60 minutes at a time.
Continuous duty
type is operated only for up to 30 minutes at a time with a rest or cooling period between operations.
Intermittent duty
The _______________ allows for easy movement of air through the windings by providing slots in the end shields or frame where air can pass through.
open-type enclosure
The type of enclosure _______________ allows for easy movement of air through the windings by providing slots in the end shields or frame where air can pass through.
open-type enclosure
The type of enclosure________ does not allow entry of air to the windings
closed-type enclosure
What should be the motor code rating of a 220V electric motor having a maximum of ¾ horsepower rating and a starting current of 30 amperes.
—USED THE MOTOR CODE TABLE—
8.8 KVA/HP (code:K)
___________ is a heat engine that converts the heat energy of fuels into mechanical energy.
internal combustion engine
- confines the expanding gases and forms the combustion chamber.
Cylinder
- confines the expanding gases and forms the combustion chamber.
Cylinder
- forms a cover on one end of the cylinder.
Cylinder head
- covers the other end of the cylinder, slides inside the cylinder to transmit the force of expansion to the connecting rod and drives the crankshaft into rotary motion.
Piston
- effects a tight seal against the cylinder wall.
Piston rings
- transmits the power of combustion from the piston to the crankshaft.
Connecting rod
- converts the reciprocating motion of the piston to rotary motion by means of a crank and two bearing supports.
Crankshaft
- stores energy during the power stroke and returns this energy during the idle strokes producing a uniform rotation.
Flywheel
-open and close the ports leading into and out of the combustion chamber.
Valves
-open and close the ports leading into and out of the combustion chamber.
Valves
-produces the spark to initiate the ignition of the fuel and air mixture.
Spark plug
-covers the crankshaft and holds the oil for the lubrication of the moving parts.
Crankcase
A __________ is a series of events occurring one after the other in a definite order and repeats itself after the last event has occurred.
cycle
Events for one cycle
Intake, compression, power, exhaust
-air or air-fuel mixture enters the combustion chamber.
Intake
- air or air-fuel mixture is compressed inside the combustion chamber.
Compression
- air-fuel mixture is ignited resulting to a very rapid expansion of the burning mixture.
Power
- air-fuel mixture is ignited resulting to a very rapid expansion of the burning mixture.
Power
- burned gases are removed from the combustion chamber, and the cycle is repeated.
Exhaust
This engine requires four strokes of the piston to complete the cycle
Four-stroke-cycle engine
A ______ is the movement of the piston from one extreme position to the other extreme position.
-Top dead center position (TDC)
-Bottom dead center position (BDC).
stroke
This engine requires only two movements of the piston to complete the cycleTwo-stroke-cycle engine. This implies that in one stroke several events have to occur.
Two-stroke-cycle engine
A the beginning of the stroke, power event is being accomplished. Towards the end of the stroke, the exhaust port along the side of the cylinder is uncovered by the piston that starts the exhaust event. Still further down, the piston also uncovers the inlet port that now starts the intake event.
Downward stroke
At the beginning of the stroke, both intake and exhaust events are occurring. As the piston goes up, the inlet port will be covered and followed by the exhaust port. From then on, compression will be accomplished, and the crankcase recharged with fresh supply of airfuel mixture.
Upward stroke
This engine uses a spark produced by a spark plug to ignite the compressed air-fuel mixture. The spark is timed to occur before the end of compression such that maximum pressure due to the expansion of burning gases is felt when the piston is ready to start its downward movement. The fuel used in this engine is gasoline and the carburettor does the metering.
Spark-ignition engine
This engine uses a spark produced by a spark plug to ignite the compressed air-fuel mixture. The spark is timed to occur before the end of compression such that maximum pressure due to the expansion of burning gases is felt when the piston is ready to start its downward movement. The fuel used in this engine is gasoline and the carburettor does the metering.
Spark-ignition engine
Uses the heat of compressed air to ignite the fuel.
Intake stroke, only air is taken and compressed to a very high degree producing a very high temperature in the combustion chamber. Towards the end of compression, pressurized fuel is injected into the cylinder.
The moment the fuel comes in contact with the hot air, spontaneous ignition and combustion occurs producing the power of the engine.
Compression-ignition engine
Determine the compression ratio of the engine with the following specification: Total volume = 70 cc, Bore = 4 cm and Stroke = 5 cm.
CR=9.76:1
Determine the compression ratio of the engine with the following specification: Total volume = 70 cc, Bore = 4 cm and Stroke = 5 cm.
CR=9.76:1
Determine the bore of the engine if its clearance volume is 7.18 cc, compression ratio is 8:1 and stroke is 4 cm.
D=4 cm
Determine the bore of the engine if its clearance volume is 7.18 cc, compression ratio is 8:1 and stroke is 4 cm.
D=4 cm
An 8x10 cm, 7 hp, 4-stroke single cylinder compression ignition engine is operating at 1850 rpm. If the clearance volume is 14 cc, determine the following: a. Piston Displacement b. Compression Ratio c. Torque output d. Average Piston Speed
a. PD=502.656 cc
b. CR= 37: 1
c. T= 2.7488 kg-m = 26.957 N-m
D. APS= 22.2 kph = 370 m/min = 6.17 m/s
