A3 - 2 Flashcards
refrigeration, heat transfer, renewable, processing
quantity of energy required to raise the temperature of a unit mass by 1K
specific heat
can be thought of as a measure of disorder in a system.
if a gas or vapor is compressed without friction and without adding or removing heat during the process, the entropy of the process remains constant
entropy, S
temp at the critical point beyond of which there are no distinct phases
critical temp
point at which a substance can exist as solid, liquid, and gas in thermodynamic equilibrium
triple point
defined by saturation points where substances exists as saturated liquid, saturated vapor or mixtures of both
saturation line
the sum of all the energies of all molecules in a system
Internal Energy, U
the amount of energy possessed by a thermodynamic system that can be transferred between the system and its environment
Enthalpy, (H = U + PV)
THERMODYNAMIC PROCESSES
no change in pressure of the fluid
Isobaric
THERMODYNAMIC PROCESSES
no change in volume of the fluid
Isochoric/ Isometric
THERMODYNAMIC PROCESSES
no change in temperature of the system
Isothermal
THERMODYNAMIC PROCESSES
no heat transfer from or to the fluid
Adiabatic
THERMODYNAMIC PROCESSES
no change of entropy of the fluid
Isentropic
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
THERMODYNAMIC PROCESSES
no change of enthalpy
Isenthalpic
a process which there is no change in enthalpy from state one to state two, h1 =h2; no work done, W=0; and the process is adiabatic, Q = 0
Throttling Process
also known as the Conservation of Energy principle, states that energy can neither be created nor destroyed, it can only change forms
first law of thermodynamics
Work done by system is usually ____ sign
positive sign (+)
Work done on the system is usually ____ sign
negative sign (-)
Law of Thermodynamics states that the state of entropy of the entire universe, as an isolated system, will always increase over time. The law also states that the changes in the entropy in the universe can never be negative.
Second Law of Thermodynamics
a reversible cycle (a cycle having a succession of reversible processes such that the system periodically returns to its initial state)
carnot cycle
2 types of carnot cycle
Carnot heat engine
Carnot refrigeration cycle
Receives heat from low temperature to higher temperature via work (of compressor)
refrigeration cycle
a device that transfers heat energy from a source of heat to what is called a “heat sink”. Moves thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one
heat pump
If the objective of the device is to perform work it is a
heat engine
a thermodynamic quantity representing the unavailability of a system’s thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system
entropy
if its objective is to supply energy to a body it is a
heat pump
if its objective is to extract energy from a body it is a
refrigerator
A pure substance is _______. It may exist in more than one phase, but each phase must have the same chemical composition.
homogeneous
After all the solid is melted, the temperature of the liquid again rises until vapor just begins to form. This state is called the _______.
saturated liquid state
Gases tend to approach the properties of ideal gas on the following conditions:
As the molecular weight ______
As the pressure _______
As the temperature ______
As the molecular weight decreases
As the pressure decreases
As the temperature increases
Momentum transfer is energy (in form of momentum) in transit due to velocity difference
Newton’s law on Viscosity
the total pressure of the mixture is equal to the sum of the individual pressures, if each gas separately occupied the space
dalton’s law of partial pressures
Heat transfer is energy in transit due to a temperature difference.
Fourier’s law
MECHANISMS OF HEAT TRANSFER
Transfer of thermal energy due to molecular vibrations
conduction
Mass transfer is mass in transit due to concentration difference
Fick’s law on mass diffusion
MECHANISMS OF HEAT TRANSFER
Transfer of thermal energy due to electron configuration
radiation
MECHANISMS OF HEAT TRANSFER
Transfer of thermal energy due to molecular motions
convection
the transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles
conduction
In the absence of any bulk fluid motion, heat transfer between a solid surface and the adjacent fluid is by ________
pure conduction
material property that appears in heat conduction analysis (normally in unsteady states) is the _______, which represents how fast heat diffuses through a material
thermal diffusivity
mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion.
convection
In gases and liquids, conduction is due to the collisions and diffusion of the molecules during their random motion
conduction
The faster the fluid motion, the _____ convection heat transfer
greater
Convection is called _____ if the fluid is forced to flow over the surface by external means such as a fan, pump, or the wind.
forced convection
the transfer of energy by _____ does not require the presence of an intervening medium. In fact, energy transfer by radiation is fastest (at the speed of light) and it suffers no attenuation in a vacuum.
radiation
The rate of convection heat transfer is observed to be proportional to the temperature difference, and is conveniently expressed by
Newton’s law of cooling
The maximum rate of radiation that can be emitted from a surface at an absolute temperature Ts (in K or R) is given by the
Stefan-Boltzmann Law
The idealized surface that emits radiation at thismaximum rate is called a ____, and the radiation emitted by a blackbody is called _____
blackbody
blackbody radiation
Convection is called _____ if the fluid motion is caused by
buoyancy forces that are induced by density differences due to the variation of temperature
in the fluid.
natural (or free)
convection
With values in the range 0 to 1, this property provides a measure of how efficiently a surface emits energy relative to a blackbody.
emissivity
Another important radiation property of a surface is its _____, α which is the fraction of the radiation energy incident on a surface that is absorbed by the surface.
Like emissivity, its value is in the range 0 to 1.
absorptivity
Heat transfer problems are often classified as being ____ (also called steady state) or _____ (also called unsteady).
steady
transient
-The term steady implies no change with time at any point within the medium, while transient implies variation with time or time dependence.
ratio of the heat transfer resistances inside of a body and at the surface of a body
biot number
ratio of convective to conductive heat transfer at a boundary in a fluid
nusselt number
ratio of the buoyancy to viscous force acting on a fluid. used in natural convection problems
grashof number
analogous to grashof number. used in force convection problems
reynold’s number
ratio of sensible to latent heat
stefan number
ratio of momentum diffusivity to thermal conductivity
prandtl number
ratio of conductive transport rate to the rate of thermal energy storage
fourier number
the high value of volume flow per ton with ____ makes it suitable for service in centrifugal compressors. _____ and R113 are the most-used refrigerants in centrifugal compressor system.
refrigerant 11
this is the most widely used refrigerant. It is used primarily with reciprocating compressors for service in household refrigeration appliances, commercial and industrial air conditioning, and in a multitude of other types of refrigeration systems. _____ possesses desirable properties, having convenient operating pressures, low power requirement per ton, and is nontoxic and noncorrosive.
refrigerant 12
like R12, is nontoxic and has a low power requirement per ton. _____ is competitive with Refrigerant 12 in small air-conditioning units. It is competitive with ammonia in industrial low-temperature systems in cases where toxicity of the refrigerant is of concern.
refrigerant 22
the vapor in the air is saturated
saturated air
air containing superheated vapor
unsaturated air
heat does not affect the temperature of the substance but damage its state
Latent heat
is the heat absorbed or given by a substance that changes its temperature
Sensible heat
sum of latent heat and sensible heat
Total heat
is the ratio of sensible heat load to the total heat load
SENSIBLE HEAT RATIO (sensible heat factor)
ratio of partial pressure of water vapor in the air to the saturation pressure corresponding to the temp of the air
relative humidity
the difference between the reading of the dry bulb and wet bulb temperature
wet bulb depression
the saturation temperature corresponding to the actual partial pressure of the stem in air or the temperature at which condensation of the moisture begin when the air is cooled at constant pressure
dew point temperature
the ratio of the air humidity ratio (SH or W) to the humidity ratio of saturated air ( SHs or Ws ) at the same temperature
degree of saturation
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
located on vertical lines angling up and to the left from the dry-bulb temperature scale
specific volume
a material quality which describes how readilty a substance vaporizes
volatility
The lowest temperature at which a liquid can give off vapor to form an ignitable mixture in air near the surface of the liquid.
flash point
are liquids that has flashpoint below 37.8°C (100°F)
flammable liquids
are substances that has flashpoints above 37.8°C (100°F) and below 93.3°C (200°F)
combustible liquids
All of the hydrogen in the fuel is converted into water and all of the carbon is converted into carbon dioxide
stoichiometric combustion
The lowest temperature at which a liquid can flow.
pour point
The lowest temperature at which the vapour will continue to burn for at least 5 seconds.
fire point
Chemical reaction of carbon and hydrogen in the fuel with oxygen in the air to form water and other exhaust products
combustion
When air-fuel ratio is lower than stoichiometric ratio
rich combustion
When air fuel ratio is higher than stoichiometric ratio
lean combustion
Sequence: Four-stroke cycle used in gasoline/petrol engines:
intake (1),
compression (2),
power (3), and
exhaust (4).
Sequence: In a 2-stroke engine, it only takes one piston stroke to complete the combustion cycle.
There’s a (1) compression stroke, then an (2) explosion of compressed fuel.
On the return, the exhaust is pushed out of the cylinder by the fresh fuel moving in. The spark plugs fire for each revolution.
BiGSHOW
➢Biomass and Biofuels
➢Geothermal
➢Solar
➢Hydroelectric power
➢Ocean
➢Wind
How much bioethanol is being sold in the market today?
10%
Solar energy is converted to heat energy for heating/cooling applications (e.g., Flat plate collectors)
Heat based (Thermal) Applications
solar energy is converted into electrical
energy.
Photovoltaics
Hydropower: > 100 MW
large scale
Hydropower: 10 MW - 100 MW
medium scale
Hydropower: < 10 MW
small scale
Hydropower: 1 MW - 10 MW
small
Hydropower: 100 kW - 1 MW
mini
Hydropower: 50 kW - 100 kW
micro
Hydropower: < 5 kW
pico
Categories of wind turbine
Depend on surface drag force
Example:
Cup type, Paddle type, Savonius, Crossflow type
drag type
Categories of wind turbine
Use the aerodynamic lift produced by the wind flow over the lifting surfaces to
propel the rotors
Example:
Single propeller, Double propellers, Three propellers, Straight-wing, Darrieus
lift type
Classification of wind turbines
As to shaft speed
- Few bladed windmills (turbines)
- Can develop a speed of more than 300 rpm
- Also referred to as “low torque windmill”
- Mostly used for electric conversion
high speed
Classification of wind turbines
As to shaft speed
- Multi-bladed windmills
- High torque windmill
- Suitable for pumping water (windpumps)
low speed
Classification of wind turbines
As to shaft orientation
- Rotor axis is perpendicular with the direction of wind
- Has no wind vane to orient the rotor
- Hence, also called as “non-directional windmill”
vertical axis
Classification of wind turbines
As to shaft orientation
- Rotor axis is parallel with the direction of wind
- Uses wind vane to orient the rotor to the direction of flow
- Also known as “directional windmill type”
horizontal type
deals on the principles and practices of processing agricultural products suitable for food/feed
agricultural processing
crops produced and harvested with normally low moisture content of about 20 to 30% and are not easy to deteriorate or spoil.
Cereal grains and legumes are the examples of these crops.
durable crops
crops that have high moisture content (30% and above) such as fruits and vegetables including dairy, meat, and fish and easily to deteriorate and spoil.
perishable crops
deals on the secondary processing of a product after it undergoes primary processing. The original shape and form of the product is altered making it more attractive for human consumption.
food processing
processing operation, which does not heavily change the physical characteristics of the product.
Drying and dehydration of grains and fruits are examples of this operation.
primary processing
processing operation which change the physical properties of the product. On-plant processing such as converting banana into catsup or mango to puree are examples of this operation.
secondary processing
- Fluid at rest
- Deals with the fluid at rest such as those fluid stored in tanks, etc.
hydrostatic
- Fluid in motion
- Deals with the various factor affecting the relationship between the rate of flow and the various pressures tending to cause or inhibit the flow.
hydrodynamics
Mass as an isolated system is neither created or destroyed by chemical reaction or physical transformation.
The mass of the product in a chemical reaction must equal the must of the reactant.
conservation of mass
The total energy of an isolated system remain constant – it is said to constant over time.
Energy can neither be created nor destroyed. It transform from one form to
another.
conservation of energy
The _______ of fluid is constant at any point in a system and there is no accumulation or depletion of fluid within the system.
rate of flow
When fluid is released and is permitted to fall or move from an initial position or a given reference plane, the fluid will have an ability to do an amount of work equal to the product of weight of fluid and its distance from reference plane.
potential energy
Fluid, in addition to the potential energy, is subjected into an internal static pressure expressed in lbs per in2, kg per m2.
pressure energy
Body in motion possesses an amount of kinetic energy.
velocity energy
Sum of the three types of energy plus the work supplied by a machine (pump) less friction of fluid in the system (conduit and fittings, etc.).
total hydraulic energy
CLASSIFICATION OF FLOW
- Fluid flows in parallel elements
- Direction of motion of each element is parallel with the other element
streamlined flow
CLASSIFICATION OF FLOW
- Fluid moves in elemental swirls or eddies
- Both velocity and direction of each element changes with time
turbulent flow
FLUID CLASSIFICATIONS
- Characterized by the rate of fluid shear that is linearly related to shear force.
- Example, oil, water, etc.
newtonian fluid
demonstrate the finite existence of the streamlined and turbulent flow.
reynolds number
FLUID CLASSIFICATIONS
- The characteristics of fluid is not linear with the shear force.
- Examples, slurries, food purees, paints, butter, mayonnaise, etc
non-newtonian fluid
- The internal resistance of fluid to shear.
- The coefficient may be considered as the coefficient of friction of fluid to fluid.
viscosity
side of pile in relation to the horizontal. It varies with the moisture content, and the amount of foreign matters present
angle of repose
- Pressure that results from force due to change in velocity of the fluid.
- Pressure taken from the direction of fluid.
dynamic pressure
flow rate varies with the cube of the orifice diameter. The exponent range from 2.50 to 2.96.
rate of flow
determines the minimum pitch of conduit
intended to move the materials by gravity.
coefficient of friction
- Pressure resulting from elevation and indicates forces perpendicular to the walls of a container.
- Pressure taken perpendicular from the direction of fluid.
static pressure
simplest and most reliable pressure gauge wherein the pressures are determined by the difference in height of the fluid inside a tube.
manometer
- Open tube pointing into the stream of fluid.
- Impact of moving fluid creates pressure head nearly equal to the velocity (V2/2g).
- Fluid static pressure or head is added to the pressure head so that a pressure gage attached to the tube indicates the sum of the velocity pressure and elevation head.
pitot tube
widely used for operation control wherein accuracies of approximately 2% are acceptable
bourdon tube
consists of spring loaded diaphragm or bellow which actuates a series of levers attached to the indicating hand.
diaphragm
- Preferable to the pitot tube when average cross-sectional velocity is desired
- Velocity indicated is a true average
- Pressure difference can be magnified by increasing the diameter ratios
*More accurate readings can be obtained - An excellent measuring device for permanent installation
venturi meter
- Based on the variation in resistance of an electrical conductor .
- with conduit temperature
- variation of the conductor temperature with the velocity of gas past the wire
- increase in velocity will permit an increase in the current flowing
- cooled wire will offer less resistance to electrical flow
hot-wire anemometer
- operates from the motion of the fluid rather than the volume that is flowing
- activated by the fluid motion
- examples are vane, propeller, or cup rotors
propeller meter
Study that deals with the principles and practices of processing agricultural products suitable for food and feeds.
Agricultural processing
Study that deals with the application and practices in converting agricultural products into different kinds and forms of food suitable for animal consumption.
Feed processing
Study that deals with the application and practices in converting agricultural products into different kinds and forms of food.
food processing
indicates the percentage volume of spaces over the volume of the product plus the volume of spaces within the product. dictated by the shape and dimension of the product as well as the roughness of the product surface.
Porosity
ratio of the weight and the volume of the product. It indicates the weight of the product at a given volume.
It is normally expressed in kg/m3 of lb/ft3.
The knowledge on this property will give an accurate estimate of determining the size of the holding bin or storage structure required for a certain product to be handled.
bulk density
angle measured from the horizontal at which a product will start to move downward over a smooth surface and smoothness of the material.
angle of friction
Basically, moisture content affects the angle of friction of the grain. Wet grains has a greater angle of friction than dried grain.
angle at which the product formed a conical shape from the horizontal after it is allowed to freely flow from discharge spout bins.
angle of repose
indicate the amount of heat transfer from one side of the material to the other side by conduction.
Thermal conductivity
Thermal conductivity of paddy grain and husk increases linearly with an\ increase of the mean bulk temperature, bulk density, moisture content.
amount of heat required to raise its temperature one degree higher when heat is added.
specific heat
amount of heat required to remove a certain amount of moisture from the product.
heat vaporization
process of allowing the grain to rest in order for the moisture at the innermost portion of the kernel to equilibrate with the outer layer.
tempering
The use of air to separate grains from other materials is an important principle of many agricultural machines.
a fan or a blower is used to create higher pressure which will cause the grain to move and separate during separation
pneumatic separation
refers to the velocity of air required to lift the products overcoming the gravity.
terminal velocity
Moisture that can be found at the surface of the product particularly at the void spaces of the materials.
free moisture
Moisture inside the tissue of the material which can be removed by heating or reducing the vapor pressure with in the material
bound moisture
Difficult-to-remove moisture and need chemical reaction by high temperature or other means in order to remove it.
chemically bound moisture
requires a sensitive analytical balance and a thermostatically controlled electrically-heated vacuum or drying oven.
oven method
determines the moisture by fractional distillation. The sample is heated at a temperature considerably above the boiling point of water in 150 ml of mineral oil.
distillation method
samples of known weight are placed on top of a platform scale of the meter where they are heated at a relatively high infrared temperature. The samples loose moisture as they are heated and give the moisture level after reaching its equilibrium level.
infrared method
commonly used by researchers. The value obtained with this method are used to calibrate all secondary type of moisture measuring devices. The steps are too cumbersome and time consuming.
primary method
types of primary method
oven method
distillation method
infrared method
types of secondary method
electric of secondary method
dielectric method
chemical method
hygrometric method
based on the principle that the electrical resistance and conductivity of a material depends upon the moisture content.
electric resistance method
determines the moisture content of the product due to its die-electric properties.
dielectric method
water is removed from the sample by the addition of chemicals that either decompose or combine with the water.
chemical methods
sample of the product is placed in a sealed container and allowed to equilibrate with the air in the container which has a known relative humidity and temperature.
hygrometric method
the study of the properties of the air, and use of the psychrometric chart are essential for an understanding of the processes involved in drying and storage of grains and other agricultural crops, and for analyzing individual requirements for a particular climatic condition.
psychrometry
temperature of the air as measured by an ordinary thermometer such as a household thermometer. The bulb is the sensitive portion of the instrument. As the temperature of the bulb increases, the liquid in the bulb expands and rises in the stem.
dry-bulb temperature
temperature of the air as measured by an ordinary thermometer whose glass bulb is covered by a wet cloth or gauze. The clean cotton wick absorbs water.
wet bulb temperature
temperature at which moisture condenses on a surface. it is the temperature at which condensation occurs when air is cooled at constant humidity ratio and constant atmospheric pressure
dewpoint temperature
weight of the water vapor contained in the moist air per unit weight of dry air. other terms used for humidity ratio are absolute humidity and specific humidity
humidity ratio
ratio of the partial pressure of water vapor, the pressure that saturated water vapor exerts at the temperature of air
relative humidity
______ of moist air is defined as the volume per unit weight of air. the specific density of the moist air is equal to the reciprocal of its _____
specific volume
_____ of a dry air-water vapor mixture id the heat content of the moist air per unit weight of dry air above a certain reference temperature
enthalpy
GENERAL CLASSIFICATION OF FANS AND BLOWERS
operate at pressures equal to or more than 1 lb/in2 (27.7 in. of water). machines in this class also include centrifugal compressors and turbo compressors
Class I: Blower
GENERAL CLASSIFICATION OF FANS AND BLOWERS
operate at pressures of less than 1 lb/in2 (27.7 in. of water). machine in this class area also called centrifugal fans, fans blowers, or exhausters
Class II: Fans
air flow is parallel to the shaft or axis. propeller fan is a generic term.
axial flow or propeller fan
used to handle large volumes of air against free delivery or low heads. this may have 2 or more blades which maybe of sheet or airfoil shape. blades may be narrow or wide, may have uniform or varied pitch
propeller fan
Similar to disk fan but is more defined for the hubs have been enlarged. The blades are warped for better efficiency and have a close radial clearance with the housing. As a result, it is able to operate against higher pressure and, therefore, has a better efficiency.
axial flow fan
Consists of an axial flow wheel within a cylinder and includes driving mechanism support, either for belt drive or for direct connection.
tube axial fan
Consists of an axial flow wheel within a cylinder, a set of guide vanes located either before or after the wheel, and a driving mechanism
support for either belt drive or direct connection.
vane axial fan
A low speed fan, capable of operating at several inches pressure under most conditions but is limited to handling clean air. It has a squirrel-cage rotor and a large number of blades.
forward curved blade fan
a binary alloy of copper and zinc
brass
the resistance of a conductor ____ when its temperature is increased
increases
a meter whose needle is initially at the center
galvanometer
automatic device that operates at a preset value
relay
modern contact surfaces are made from ____ alloys
silver
unit of magnetic flux in SI is
weber
a small lamp used to indicate that a circuit is energized
pilot lamp
an instrument that measures the voltage or electrical pressure in a circuit
voltmeter
good conductors
silver
gold
copper
brass
steel
aluminum
iron
sea water
good insulator
rubber
glass
oil
diamond
dry wood
plastic
a good capacitor has a _______ resistance
very high
the energy stored in an electrolytic cell is ________
a chemical
the most common usage of resistors in electronic circuits is to _______
a) limit current
b) introduced a voltage drop
c) generate heat
d) all of these
d) all of these
a substance that cannot be decomposed any further by a chemical reaction
element
admittance in AC circuit is a parameter equivalent to the ______
reciprocal of impedance
1 hp is equivalent to ______W
746 W
in aming a resistance test, remember that the resistance of a short circuit is ______
approximately zero
grease is a lubricant that is basically a combination of _____
oil and soap
electromotive force is measured by a
voltmeter
a potentiometer is used to control the _____ of the circuit
voltage
the efficiency of a cell _____ that of a DC generator
more than
an open coil can be detected by reading
high resistance
a pipe bending tool
a) pipe vise
b) hickey
c) pipe reamer
d) gimlet
b) hickey
cells are connected in _______ when high voltage, as well as high current is desired
series-parallel
this is the greatest effective difference of potential that exist between any two conductors of a circuit
voltage
electric current in a wire is a flow of ______
free electrons
the device to transform AC electricity to dc electricity
converter
