A3 - UP Flashcards
Area 3 from UP Reviewers (Farm elect, thermody, heat transfer,
Certain types of crystals produce a voltage when subjected to pressure.
Pressure (Piezoelectricity)
Voltage is produced when the junction of two unlike metals is heated. Thermocouples use the principle of thermoelectricity.
Heat (Thermoelectricity).
solar or photo cells convert radiant energy to electrical energy.
Light (Photoelectricity
Symbol and unit for conductance
G, siemens
if an object contains more number of total electrons than the total protons
Negatively charged
if an atom contains fewer number of total electrons than the total protons
positively charged
- The result of non-random movement of electrons
- Defined as the rate at which electrical charge flows
- Measured in amperes (A)
- One ampere is equal to one coulomb per second
current
- The ability of a material to resist the flow of electrical charge when subjected to a given potential difference
- Electrical resistance is measured in ohm (Ω)
Electrical Resistance
The lower the resistivity of the material, the _____ conductor it is
better
Conductors are materials which has ____ resistance to electron flow
low resistance
Insulators are materials which has ____ resistance to electron flow
high resistance
_____ are materials having an intermediate resistance to electron flow; usually used in construction of solid state electronic devices such as diodes and transistors
Semiconductors
Conductance is the reciprocal of _____, measured in mhos
resistance
phenomenon when conductors lose their resistance in extreme cold
superconcuctivity
States that the current flowing in a circuit varies directly with the electrical pressure and inversely with the opposition
ohm’s law
Because charge cannot be created but must be conserved, the sum of the current in a node must be equal to zero
Kirchhoff’s current law
the ability of material to conduct electricity; reciprocal of resistivity
conductivity
The net voltage around a close circuit is zero
Kirchhoff’s voltage law
- The power dissipated by an electrical circuit is given by:
- The common unit of electric power is watt.
- An instrument called a wattmeter measures power. The wattmeter gives a reading of the product of the current and voltage in a circuit.
Power Calculations (Joule’s Law)
The value of the _____depends on the kind of opposition offered. It is never greater than 1.
power factor
Power factor is equal to ____ for heaters, electric ranges and incandescent lamps.
The opposition is pure resistance.
one (1)
Power factor is between ____ for electric motors.
0.6 to 0.8
From the point of the view of the load, any network composed of ideal voltage and current sources, and of linear resistors, may be represented by an equivalent circuit
consisting of an ideal voltage source in series with an equivalent resistance.
Norton’s theorem
Characterized by non-variant current flow in one direction at all times
Common source are batteries, thermocouples, solar cells, and rotating _____ generators
direct current (DC)
Characterized by an alternating flow of in two directions
Most common variation is of a sine wave
Alternating Current (AC)
When voltage and current are in phase, all the power is ____
positive
_____, in VAR units, is the power below the axis. It is “watt-less” and does no useful work. VAR means volt-ampere-reactive.
Reactive power
Coils of wire such as those found in transformers, relays, and motors have ______
inductive reactance
the property to oppose current change.
inductance
Current in AC circuit with pure inductance will lag the voltage by ____
90 deg
The amount of electric charge that a capacitor receives for each volt of applied potential is called its ___
measured in farads but practical devices are rated in terms of
microfarads.
capacitance
Power factor improvement can be accomplished either by ____ of series or parallel-connected capacitors.
addition
are lines of force surrounding a permanent magnet or a moving
charged particle.
magnetic fields
the quantity of magnetic field force or “push”; also known as magnetic potential difference; analogous to electric voltage (emf).
Magnetomotive force (mmf)
the quantity of total field effect or “substance” of the field; analogous
to electric current.
magnetic flux
the amount of field force (mmf) distributed over the length of the electromagnet.
magnetic field strength (intensity)
the amount of magnetic field flux concentrated in a given area.
magnetic flux density
Completely describes the laws of electromagnetism and its effect based on four equations or theories developed by Gauss, Ampere and Faraday.
Maxwell’s Equations
describes that the electric field due to electric charges can be derived by Coulomb’s Law.
Gauss’s law for electricity
states that the net magnetic flux through any (real or imaginary) closed surface is zero. Magnetic field lines do not start or stop at any point in space, but form a close loop thus any magnetic field line entering a closed surface must also leave that surface, so the net flux is zero.
Gauss’ law for magnetism
describes the production of magnetic fields not only by electric currents but by changing electric field as well.
Ampere’s law
describes the production of electric fields as a result of changing magnetic fields.
Faraday’s law of induction
voltage induced by a changing magnetic flux
induced emf
current produced during electromagnetic induction
induced current
There are three standard types of DC generators:
(a) shunt generator;
(b) series generator; and
(c) compound generator
There are three general classes of synchronous generators:
a) slow-speed engine-driven type
b) moderate-speed waterwheel-driven type
c) high-speed turbine-driven type
an engine that has 75-90 rpm, though runs as high as 150 rpm
slow-speed engine-driven type
an engine that has 80-90 rpm and higher
moderate-speed waterwheel-driven type
The total power output for a 3-phase system is a _____
constant value
The main reason for the use of 3-phase systems is that for the same voltage and current, a 3-wire, 3-phase system will deliver ______ as much power as a 2-wire, single-phase system.
1.73 times
an engine that has 720-3600 rpm
high-speed turbine-driven type
________ are the most common in the home, on the farm and in light industry. It requires some type of starting mechanism.
Single-phase motors
__________ are inherently self-starting. They are common in ratings from ½ hp to 400 hp.
Three-phase motors
If the equipment can be successfully operated by hand, a ______ motor will do.
¼ hp motor
common motor enclosure types
a) drip proof
b) splash-proof
c) totally enclosed
Transformers only work with ____ voltages, not _____ voltage. Thus, they may be classified as an AC device and not a DC device.
changing voltages, not steady voltages
The primary winding has more turns than the secondary.
Step-up transformer
The primary winding has fewer turns than the secondary.
Step-down transformer
States that the induced voltage in a coil is always in a direction so as to oppose the effect which is producing it.
The Lenz’s law
refers to the portion of electric conductors that extends from the service entrance to an outlet or a certain group of outlets. It connects the loads to the final overcurrent protection device.
Branch circuit
No point along the floor line in any wall space should be more than _____ from
a receptacle outlet.
Any wall space greater than 0.6 m (2 ft) shall have an outlet.
1.8 m (6 ft)
Any wall space greater than _____shall have an outlet.
0.6 m (2 ft)
Provide one 20 A circuit for each ______ or one 15 A circuit for each 35 m2 (375 ft2) floor area.
46 m2 (500 ft2)
At least _____ wall switch controlled lighting outlet shall be installed in every habitable
room.
one
Allow _____ outlets for each 15 A circuit and ______ for each 20 A circuit.
8 to 10 outlets
10 to 12 outlets
A factor of ________ is used for all floor area excluding open porches, garages, basements or unused or unfinished spaces not adaptable for future use.
32 watts/m2 (3 watts/ft2)
the use of colors of conductor covers in the wiring connections
polarizing
white wire is always the _____ wire
neutral wire
_____ are those which are larger than the wires.
cables
Wires and cables are either stranded or solid.
is grounding of equipment not intended to be at a voltage potential different from the earth.
It is necessary to prevent electric shock to persons coming into contact with metallic objects which, either intentionally or accidentally, form part of the electric system.
equipment grounding
The resistance of the human body varies from about _____ Ω when dry to about
____Ω when wet (including the effects of perspiration).
500,000 Ω
300 Ω
Therefore, voltages as low as 30V can cause sufficient current to be fatal
is grounding of current-carrying portions of a system.
The principal reason is to limit the voltage between any conductor and ground from rising above a safe level due to some fault outside a building.
system grounding
green wire is the ____wire
grounding wire
reed or black wires are ____ conductors
hot conductors
white wires are to be connected to _____ colored terminals, and red or black wires to ____colored terminals
silver-colored terminals
brass-colored terminals
all switches are in the ____ conductors
hot conductors
Two basic classes of devices are ________
fuses and circuit breakers
______ is never to be interrupted by a fuse, circuit breaker, switch or any other device.
Grounded neutral
types of distribution centers
a) indoors
b) outdoor
c) pole
The pole type should be located at the ______
electrical load center of the
farmstead
The best location for indoor type distribution center is the position closest to the equipment having the largest wattage rating
The outdoor type should be nearest to the
______
electrical load center
allowable voltage drop
2%
COMMON TYPES OF LIGHT SOURCES
cheap, instant start and re-start, simple and compact installation
low efficacy, short life, sensitive and critical on voltage changes, high maintenance costs, more heat is produced than light
incandescent lamps
COMMON TYPES OF LIGHT SOURCES
efficacy is higher than incandescent lamp, 20% of input energy is converted to light, 80% to heat
long life but life span is affected by the number of times lamp is switched on and off
fluorescent lamp
other types of common light source
mercury lamp
metal halide lamp
high pressure sodium lamp
low pressure sodium lamp
tungsten-halogen lamp
intensity of light is measured in _______ in english system, and ___ in the SI system
footcandles (fc)
Lux (lx)
2 general classes of thermodynamics properties
extensive property
intensive property
its value for an overall system is the sum of its values for the parts into which the system is divided; varies directly with the mass i.e. total volume.
extensive property
its value is independent of the size or extent of a system and may vary from place to place within the system at any moment i.e. pressure, temperature and density.
intensive property
indicates thermal state and the ability to exchange energy with a substance in contact with it. It is a measure of the internal energy of a body.
temperature
measured above existing atmospheric pressure. It is the excess of the absolute pressure over the atmospheric pressure.
gage pressure
the number of degrees above absolute zero expressed in Kelvins or Rankine.
Absolute temperature, T
is the measure of pressure above zero.
absolute pressure
mass per unit volume
densityvolume
per unit mass, reciprocal of density
specific volume
the quantity of energy required to raise the temperature of a unit mass by 1Kelvin
specific heat, Cp
LAWS OF THERMODYNAMICS
when two bodies have equality of temperature with a third body, they in turn have equality of temperature with each other
zeroth law
LAWS OF THERMODYNAMICS
also known as the Conservation of Energy principle, states that energy can neither be created not destroyed, it can only change forms.
first law
LAWS OF THERMODYNAMICS
deals with the quality of energy (energy degradation).
second law
It is impossible to construct a device that will operate in a cycle and produce no effect other than the raising of a weight and the exchange of heat with a single reservoir.
kelvin-plank statement
It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a cooler-body to a hotter body.
clausius statement
states that the entropy of a perfect crystal is zero at the absolute zero of temperature.
third law
amount of heat added to or subtracted from a substance when unit weight of the material changes 1° in temperature.
Coefficient of Thermal Capacity
fraction by mass of the vapor in the liquid-vapor mixture.
Quality (x) of a two-phase mixture
the amount of heat required to change unit mass of a pure substance from the saturated liquid state to the saturated vapor state, the pressure (or temperature) remaining constant.
enthalpy or latent heat of vaporization
the amount of heat required to change unit mass of a pure substance from the solid state to the vapor state, the pressure (or temperature) remaining constant.
Enthalpy (or latent heat) of sublimation
the amount of heat required to change unit mass of a pure substance from the solid state to the liquid state, the pressure (or temperature)
remaining constant.
Enthalpy (or latent heat) of fusion
The 3 two-variable equations of state for an ideal gas:
boyle’s law
charles’ law
gay-lussac’s law
The time rate of energy transfer by conduction is quantified macroscopically by ________ which states that the rate of heat transfer across any plane normal to the x direction, Qx, is proportional to the wall area, A, and the temperature gradient in the x direction, dT/dx:
Fourier’s law
occurs when heat moves from one place to another by means of currents that are set up within some fluid medium.
Heat transfer by convection
These currents are known as convection currents and result from the change in density that is brought about by the expansion of the heated portion of the fluid.
occurs in the form of a wave motion similar to light waves wherein the energy is transmitted from one body to another without the need for
intervening matter.
heat transfer by radiation
Heat energy transmitted by wave motion is called radiant energy.
ratio of rate at which a given surface absorbs radiation to the rate of radiation of a black body at the same temperature.
absorptivity of a surface
temperature of surrounding medium.
hypothetical body capable of absorbing all radiation at the maximum rate for a given temperature.
black body
Heat Balance - is the difference between the heat gained (or generated) within the
building and the entire heat test from the building.
is the change of heat (energy) required to change unit mass of a substance from a liquid to a gas.
Latent Heat of Evaporation
expressed as the ratio at which the given surface emits radiation to the rate of radiation of a black body at the same temperature
Emissivity of a Surface
Heat Capacity or Specific Heat - refer to the ratio of the heat capacities of the material to
that of water.
is the heat for evaporation of a saturated liquid into a saturated vapor. It is the heat gained or lost without a change in temperature when a substance passes from one state to another as a solid, liquid, or gas.
Latent Heat -
the heat energy required to raise the temperature of unit mass of a substance by 1°C.
Specific Heat
specific volume is the volume of space occupied by a pound of dry air at standard atmospheric pressure. expressed in m³/kg dry air.
Specific Volume
the amount of heat transmitted in unit time across unit area through unit thickness for unit temperature change.
Thermal Conductivity
provides a heat transfer surface through which heat can pass from the refrigerated space or product into the vaporizing refrigerant.
evaporator
conveys the low-pressure vapor from the evaporator to the suction inlet of the compressor.
suction line
removes the vapor from the evaporator and raises the temperature and pressure of the vapor to a point such that the vapor can be condensed with normally available condensing media.
vapor compressor
delivers the high pressure, high-temperature vapor from the discharge of the compressor to the condenser.
“hot ga” or discharge line
provides a heat transfer surface through which heat passes from the hot refrigerant vapor to the condensing medium.
condenser
provides storage for the condensed liquid so that a constant supply of liquid is available to the evaporator as needed.
receiver tank
carries the liquid refrigerant from the receiver tank to the refrigerant flow control.
liquid line
meters the proper amount of refrigerant to the evaporator and reduces the pressure of the liquid entering the evaporator so that the liquid will vaporize in the evaporator at the desired low temperature.
refrigerant flow control
substance employed as the heat absorber or cooling agent is called the
also a medium of heat transfer which absorbs heat by evaporating at a low
refrigerant
Classification cooling process according to the effect the absorbed heat has upon the refrigerant:
the absorbed heat causes a change in the physical state of the refrigerant (either melting or vaporizing).
latent
Classification cooling process according to the effect the absorbed heat has upon the refrigerant:
the absorbed heat causes an increase in the temperature of the refrigerant.
sensible
Secondary refrigerants include _____ and ____
brines and antifreezes.
Two of the most popular brines are calcium chloride and sodium chloride solutions.
Dry air is composed mainly of ______ (78%) and ________(21%), the remaining 1% being made up of ______ and minute quantities of other gases such as hydrogen, helium, neon and argon.
nitrogen
oxygen
CO2
is the temperature at which the water vapor in the air is saturated.
dew point temperature
water vapor in the air
humidity
mass of water vapor per unit volume of air
absolute humidity or vapor density
ratio of the actual partial pressure exerted by the water vapor in any volume of air to the partial pressure that would be exerted by the water vapor if the water vapor in the air is saturated at the temperature of the air.
relative humidity
also called as specific humidity, is an expression of the mass of water vapor per unit mass of dry air.
humidity ratio
also called as percentage humidity, is the ratio of the mass of water vapor in the air per unit mass of dry air to the mass of water vapor required for saturation of the same air sample.
saturation ratio
temperature as measured by an ordinary dry bulb thermometer
dry bulb temperature of air
temperature as measured by a wet bulb thermometer. A wet bulb thermometer is an ordinary thermometer whose bulb is enclosed in a wetted cloth sac or wick.
wet bulb temperature of air
mixture of dry air and water vapor is the sum of the enthalpy of the dry air and the enthalpy of the water vapor.
enthalpy
difference between the dew point and dry bulb temperature of air
degrees of superheat
refers to a rate of heat transfer attributable only to a change in dry-bulb temperature of the air
sensible heating or cooling
may be adiabatic or with addition of heat
humidification
results in a reduction of both the dry-bulb temperature and the humidity ratio
cooling and dehumidification
the water vapor from the air is absorbed or adsorbed by a hygroscopic material
chemical dehumidification process
a type of valve that is installed in the line to block flow completely when it is closed. This is installed wherever any component of the system should at certain times be isolated from the remainder of the system.
shutoff valve
a type of valve that is installed in the suction line to maintain a sufficiently high pressure in an evaporator to prevent freezing or excessive dehumidification of air in an air cooling coil.
back-pressure valve or
evaporator-pressure regulator
a type of valve that is electrically powered magnetic valves which serve as automatic shutoff valves. These are often installed in the liquid line and close when the compressor is not operating.
solenoid valve
A check valve which permits flow of fluid in either direction but which limits excessive flow in one direction. If the designated flow is exceeded, the valve
automatically closes.
excess flow valve
A valve designated as a safety device to open, and remain open, to discharge a fluid whenever the fluid pressure reaches the start-to-discharge setting of the valve. When the fluid pressure drops below this setting, the relief valve automatically
closes.
pressure relief valve
A manually operated valve specially designed to accomplish rapid shutoff to fuel flow to dryer.
quick acting valves
consists of a wheel or rotor within a scroll spiral type housing. The air enters parallel to the shaft, makes a 90° turn in the fan wheel, and is discharged from the wheel (and housing) in a radial manner.
radial flow or centrifugal fan
it has about 12 blades, essentially flat and tilted backward from the direction of wheel rotation. It is a high-speed type of fan with a self-limiting horsepower characteristic. It is the most efficient and more expensive. It cannot be recommended for dirty air.
backward-curved blade
it has a large number of blades, i.e. up to 60, narrow in the radial dimension but wide parallel to the shaft and facing forward in the direction of rotation like a scoop. It is a low-speed fan and is limited to handling clean air.
forward-curved blade
it has a smaller number of blades – from 6 to 20 – and the blades are essentially in a plane radiating from the shaft. The blades are normally about 2 to 3 times as long radially as they are wide. It usually has a larger housing than the other types. It has the ability to handle dirty air and to convey materials that go through the fan.
straight or double-curved fan
airflow is parallel to the shaft or axis.
axial-low or properller fan
may have two or more blades which may be of sheet steel or airfoil shape.
The blades may be narrow or wide. They may have uniform or varied pitch.
This is used to handle large volumes of air against free delivery or low heads.
This is suited for ventilation of rooms and air ducts of low resistance.
This is characterized by excessive noises at high speeds.
propeller
distinguished by large hubs and short blades, in addition to stationary straight vanes on the discharge sides of the fan to prevent rotation or swirling of the air.
vane axis
this is similar to a vane-axial fan except that it does not contain guide vanes. It is simpler and somewhat less efficient than the vane-axial.
tube axial
temperature of the surrounding air
ambient temperature
transmission through or by means of conductor, distinguished in the case of heat from convection and radiation
conduction
transference of heat or electricity by moving masses of matter, as by currents in gasses and liquids caused by differences in density, or by electrically charged particles across a spark gap
convection
energy is emitted from molecules and atoms owing to the internal changes. also the combined process of emission, transmission, and absorption of radiant energy
radiation
is a rice particle with length of 6/8 or more of the length of the whole unbroken milled rice kernel.
head rice grain
a rice particle with a length of 3/8 or more but shorter than 6/8
large broken milled grain
are rice particles which will not pass through a perforated sieve with a round perforation of 1.4 mm but length of the grain is shorter than 3/8.
small brokens
is composed of rice particles which will pass through a sieve with a round perforation of 1.4 mm diameter.
brewer’s rice
or binlid in filipino language
Common ric mill in the phil
more popular and most patronized mill in rural areas. It is composed mainly of a metal cylinder with rectangular protrusions running along its whole length and a hollow cylinder casing. It works on the principle of friction in dehulling the paddy. A (low) recovery of 50 to 60% is obtained.
kiskisan
technically known as the under runner disc which consists of 2 horizontal cast iron disc partly coated with an abrasive layer. The top disc is fixed in the frame housing while the bottom disc rotates. This mill is equipped with a vertical cone-shaped polisher.
cono-type rice mill
Common ric mill in the phil
most advanced milling machine that works on the principle of centrifugal force and impact
centrifugal type
Common ric mill in the phil
this falls under friction type machines consisting of two rubber rolls rotating in opposite directions at different speeds. One roll moves about 25% faster than the other. The difference in peripheral speeds subjects the paddy grains falling between the rolls to a shearing action that strips off the husk. The clearance between the rolls is adjustable and is kept at less than the thickness of the grain. It has a 70% milling recovery.
rubber roll
types of paddy separator
makes use of the difference in specific gravity and buoyancy of the paddy grains and brown rice
compartment-type rice separator
types of paddy separator
makes use of the difference in specific gravity and length
tray type separator
makes use of the difference in width and thickness
seven-type separator
Process of bran removal
uses rough surface, which is an abrasive stone, to break and peel the bran off the grain
abrasion process
Process of bran removal
uses friction between the grains themselves to break and peel off the bran
friction process
refers to the process of removing small bran particles that stick to the rice surface after whitening and gives the rice grain a shiny appearance
polishing
the processs of removing the outer and sometimes inner bran layer
whitening
kinds of whitening machines widely used in the industry
is more compact than the vertical abrasive whitener. The machine consists of an abrasive roll (emery stone attached to a steel shaft) operating in a cylindrical metal perforated screen mounted horizontally.
horizontal abrasive whitener
kinds of whitening machines widely used in the industry
are often called jet or pneumatic pearlers. This machine uses the friction process in which the bran is peeled off by friction of the rice grains. Steel hullers are also used as friction-type whiteners.
horizontal friction whiteners
a warehouse used for storing paddy or rice either in bulk or bag.
godown
kinds of whitening machines widely used in the industry
available with the cone directed either up or down, but with no difference in performance or capacity.
vertical abrasion whitener
Milled corn grains where the outer covering and germs have been removed.
corn grits
small metal probe for taking samples of paddy or rice from bags or from bulk containers.
trier
Corn grains with relatively large amount of hard endosperm on the sides and the inner portion is composed of soft starch.
flint corn
embryo of the kernel removed during the degermination process
germ
outer covering of the corn kernel removed during the milling process
pericarp or hull
attachment of the kernel to the cob; the entryway of nutrients, water, etc. to
the kernel
tip cap
combination of germ, tip cap, pericarp, and corn grits
bran
milled corn grains where the outer covering (pericarp), germ (embryo), and tip cap have been removed leaving only the endosperm that passed through different sieve
sizes
corn grits
load applied at a point or along a line
Concentrated load
load spread over a large area
Distributed load
load is equal over all portion of the contact area
Uniformly distributed load
include the weights of various structural members and materials permanently attached to the structure (e.g. weight of roofing or floor covering, columns, beams, girders, walls, windows, etc.)
Dead loads
include loads imposed during building construction (e.g. roofing process) and after construction (e.g. re-roofing operations, air conditioning and mechanical equipment installation and servicing)
roof live loads
gravity loads which are not permanently applied to the structure
Live loads
occurs when structures block the flow of wind converting wind’s kinetic energy into potential energy of pressure.
wind loads
based on the occupancy or use of the building (human occupants, furniture, stored materials, etc.)
floor live loads
