Refri Flashcards
In polytropic process, PV^n = C, if the volume of n is infinitely large, the process is _______
Isometric
Branch of science that deals with the process of
reducing or maintaining the temperature of the
surrounding.
Refrigeration
It is defined as the quantity of heat extracted from a cold body or space to be cooled in a given time
Refrigerating effect, N
It is the quantity of heat required to raise or lower the temperature of one kg of water or ice through one kelvin or 1 celcius in one second
Specific heat
These machines are expressed by cooling capacity
Capacity of refrigerating
The standard unit of expressing capacity of refrigerating machine
Ton of refrigeration
Quantity of heat abstracted to freeze one ton of water into one ton iof ice in a duration of 24 hrs at 0 C
One ton of refrigeration, TR
Defined as ration if heat extracted in a given time (refrigerating effect)to work input
Coefficient of performance ,CoP
Ideal refrigerants
- High latent heat of evaporation
- Low boiling point and low freezing point
- Non toxic and should non corrosive
- Non flammable and non explosive
- High thermal conductivity
- Easy to handle
- Low specific volume of vapor
- High coefficient of performance
Working medium which is used for cooling the substance by absorption of latent heat
Primary refrigerant
Refrigerants that provide refrigeration by undergoing a phase change process in evaporator
Primary refrigerant
These systems use air as their refrigerant which compresses and expands to create heating and cooling capacity
Air refrigeration
A system that uses a heat source to provide the energy needed to run the cooling process.
Absorption Refrigeration
Uses two types if coolant; the first coolant performs evaporative cooling and is then absorbed into the second coolant
Absorption Refrigeration
Pulls low pressure vapor from the evaporator
Compressor
Compresses this vapor into a high temperature, high pressure gas so that it may be condensed
Compressor
Removes heat from refrigerant by providing a medium at a lower temperature to which the heat may flow and be dissipated.
Condenser
Super heated gas converted to subcooled liquid
Condenser
And expansion device which throttles high pressure liquid to low pressure liquid
Thermal expansion valve
The low pressure liquid from TXV has a saturation temperature well below that of the surrounding medium
Evaporator
This results in a rapid boiling of refrigerant with heat being absorbed from the surrounding to desired cooling temperature
Evaporator
Condition of refrigerant after passing through the condenser in a vapour compression system
Saturated liquid
Indicates the velocity of molecules of a substance
Temperature
Pressure ____ when volume increases
Drops
Process 1-2
Isentropic compression
The rate of heat removal from the evaporator or low temperature space
Refrigerating Effect, QA
The ratio of the refrigerating effect divided by the power input and is usually express in BTU/hr per watt
Energy Efficiency Ratio, EER
Process of conditioning the air cooling according to human comfort, irrespective to external conditions
Air conditioning
If the condition of mixture lies in the saturation line, the air is said to be _____
Saturated
Rate of heat transfer attributable only to a change in dry -bulb temperature of the air
Sensible heat / cooling
May be adiabatic or with addition of heat
Humidification
Results in a reduction of both the dry bulb temperature and humidity ratio
Cooling and dehumidification
The water vapor from the air is absorbed or adsorbed by hygroscopic material
Chemical and dehumidification process
The temperature to which the air would have to cool (at constant pressure and constant vapor content) in order to reach saturation
Dew point temperature
Dew point temperature will never be _____ air temperature
Greater
It is amount of water vapor in the air
Humidity
Amount of water vapor divided by the amount of dry air in certain volume of air at a particular temperature
Absolute humidity
The hotter the air is, the ____ water it can hold
The more water
Ratio of current absolute humidity to the highest possible absolute humidity
Relative humidity
Air cant hold any more water
100% relative humidity
Aka specific humidity
Humidity ratio
Temperature as measured by an ordinary dry bulb thermometer
Dry bulb
Mixture of dry air and water vapor
Sum of enthalpy
Defined as the process of achieving temperature below ambient, with the aim of cooling a product or space to the required temperature
Refrigeration
Machine used to extract heat from the body low temperature and then rejects the heat to high temperature body
Refrigerator
Machine used to heat a medium warmer than the surrounding
Heat pump
Specific heat of water in KJ/kg K
- 19 KJ/kg K
Specific heat of ice in KJ/kg K
2.1 KJ/kg K
Latent heat of ice
144 BTU/lb
335 KJ/kg
One ton of refrigeration
12, 000 BTU / hr
3.52 KJ / hr
Any substance that absorbs heat through expansion and vaporisation process and loses heat due to condensation in a refrigeration process
Refrigerants
Synthetically produced and were developed as the the Freon Family of refrigerant
Halocarbon Refrigerants
Commonly used in domestic, industrial and commercial purposes due to wide range of boiling points at atmospheric pressure
Halocarbon Refrigerants
Ozone unfriendly refrigerants
Halocarbon Refrigerants
Halo carbon refrigerant example
R11
R12
R13
A stable mixture of two or several refrigerants whose vapour and liquid phases retain identical compositions over a wide range of temperature
Azeotropes Refrigerants
Refrigerants whose code starts with digit 5
Azeotropes Refrigerants
A mixture is one whose composition in liquid phase differs to that in vapour phase
Zeotropes Refrigerant
Refrigerants designated by R followed by number
Inorganic refrigerant
Refrigerants that are highly flammable and required additional safety precautions during its use as refrigerant
Hydro-carbon refrigerant
Refrigerants Dominant in domestic market like household refrigerators and freezers
Hydro-carbon refrigerant
Substance already cooled by the primary refrigerant and then employed for cooling purposes.
Secondary Refrigerant
Most widely used refrigerant
Refrigerant 12
High pressure refrigerant where high operating pressures are required for efficient operation
CO2
Refrigerants used in such low temperature application such as frozen food
Ammonia
Solid carbon dioxide having a temperature of -78 C.
Dry Ice Refrigeration
Ordinary ice is used for keeping the space at temperatures below the surrounding temperature
Ice refrigeration
It applies the principle of boiling water under 100 C by the process of reducing the pressure on the water surface below atmospheric pressure
Steam Jet Refrigeration
It is simply the process of reducing the pressure of the liquid refrigerant as it passed through the expansion device
Throttling Refrigeration
In these types of refrigeration systems, the refrigerant vapour is compressed by means of centrifugal, screw or reciprocating compressor
Mechanical Compression Refrigeration
This system use water to cool the air bought in from outside
Evaporative Cooling
Water is pumped onto the pad through which air passes and the air losses its heat from the water
Evaporative Cooling
This is a system that uses a heat source to provide energy needed to run the cooling process
Absorption Refrigeration
A system where normally works on the principle of the Peltier Process
Thermoelectric Refrigeration
The working agent employed in these types are like ammonia, carbon dioxide, sulfur dioxide and Freons
Vapour Refrigeration
This type of refrigeration uses liquid refrigerant in a closed system that circulates the refrigerant through 4 stages in which it is compressed and expanded to alternate between vapor and liquid form without leaving the refrigerating area
Vapour Compression Refrigeration
These systems are primarily used where high pressure is not readily available.
Vapour Absorption Refrigeration
In these systems, water is used as refrigerant and a solution of lithium bromide in water is used as the absorbent
Vapour Absorption Refrigeration
It is the most efficient refrigeration cycle operating between two specified temperature level.
Reversed Carnot Cycle
The most widely used cycle for refrigerator, air conditioner and heat pump
Vapor Compression Refrigeration
Assumption for ideal vapor compression cycle
- no frictional pressure drops
- Heat losses to the surrounding are ignored
- Compression process is isentropic
- Refrigerant flows at constant pressure through the evaporator and condenser
- Irreversibility with evaporator, condenser, and compressor are ignored
Provides 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 evaporator to the suction inlet of the compressor
Suction line
Removes vapor from the evaporator and raises the temperature and pressure of the vapor to a point such 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 gas 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 at the desired low temperature
Refrigerant flow control
Valve that is installed in the line to block flow completely when it is closed.
Shut off valve
It 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
Electrically powered magnetic valves which serves as automatic shut off valves
Solenoid valve
Some oil escapes from all compressor into the discharge line. To recover as much of this oil as possible before it goes through the condenser and collects in the evaporator, ______ may be installed
Oil separator
These are installed in the suction and discharge lines to reduce transmission of vibration from the compressor.
Vibration eliminators
Contain desiccant such as silica gel or activated alumina which adsorb moisture
Driers
Prevents foreign particles from flowing through the refrigerating system
Filters
Short transparent fitting that allows the flow of refrigerant to be viewed
Liquid indicator
Its purpose is to heat the vapor coming from the evaporator while it subcools liquid flowing between the condenser and expansion valve
Heat exchanger
A vessel which stores liquid refrigerant
Liquid receiver
Prevents suction vapor from carrying slugs of liquid to the compressor from the evaporator
Liquid accumulator
Removes air from the system
Purger
Whenever a cooling coil operates with surface temperature below 32 F, frost is likely to form on the coil, what should be installed
Defrosting
Type of fan that consists of a wheel or rotor within a scroll spiral type housing.
Radial flow or centrifugal fan
The air enters parallel to the shaft makes 90 degrees turn in the fan wheel, and is discharged from the wheel in a radial manner
Radial flow or centrifugal fan
It has large number of blades, ie 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.
Forward curved blade
It has 12 blades and tilted backwards from the direction of wheel rotation
Backward curved blades
It is a low speed fan and is limited to handling clean air
Forward curved blade
It is a high speed type of fan with a self limiting horse power characteristics.
Backward curved blades
- Smaller number of blades
- blades in plane radiating from the shaft
- has the ability to handle dirty air
Straight or double curved fan
Air flow is parallel to the shaft or axis
Axial -flow or propeller fan
Used to handle large volumes of air against free delivery or low heads
Propeller
Suited for ventilation of rooms and air ducts of low resistance
Propeller
Normally used for delivery of air for pressure to 2.24 kpa and for ventilation systems where space is valuable or head room is limited
Vane axial
Same with vane axial except it does not contain guide vanes
Tube axial
Simultaneous control of temperature, humidity, air movement and air quality of air in the space
Air conditioning
The study of properties of mixture of air and water vapor
Psychrometry
Graphical representation of the thermodynamics properties of moist
Psychrometric chart
A balanced conditions of air and water occurs when the air has become saturated with water vapor
Air Moisture Content
A mixture of dry air and water vapor
Moist air
Mechanical mixture of gases and water vapor
Air
Dry air composed of
Nitrogen 78%
Oxygen 21%
Carbon dioxide, hydrogen, helium, neon and argon 1%
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 if air
Absolute humidity or vapor density
Ratio of actual partial pressure exerted by the water vapor in any volume of the 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
Aka Specific humidity
Humidity ratio
Temperature as measured by an ordinary dry bulb thermometer
Dry bulb temperature of the air
An ordinary thermometer whose bulb is enclosed in a wetted cloth sac or wick
Wet bulb temperature of the air
Difference between the dew point and dry bulb temperature of the air
Degrees of superheat
If the condition of mixture lies on the ______, the air is saturated
Saturation line
Refers to rate of heat transfer attributable only to the change in dry bulb temperature of the air
Sensible heat or cooling
Made up of the heat that must be removed from the refrigerated product in order to reduce the temperature of the product to the desired level
Product load
Defined as uncontrolled entry of unconditioned outside air directly to the building
Infiltration Load
Heat loss or heat gain due to temperature difference across a building element.
Transmission load
Heat gains due to the release of energy within a space
Internal load
Amount of heat gain in the space due to lighting depends in the wattage of the lamps and the type of fixture
Internal load
Heat generated by the refrigeration equipment itself as it performs certain task.
Refrigeration Equipment Load
If the wet bulb and dry bulb reading of air temperature are identical
The air is saturated
Refrigerant commonly used for air conditioning of passenger aircraft
Ammonia
R-11
CO2
The amount of heat required to change the temperature of one unit of substance into one degree unit of temperature
Specific heat
It is the removal of moisture in air being circulated in a given space
Dehumidification
Ratio of useful refrigeration to the net work
Coefficient of Performance
The heart of vapor compression system is____
Compressor
The term used to the ratio of the partial pressure of the water in saturated air at the same temperature
Relative Humidity
Freon group of refrigerant are…
Non toxic and non inflammable
Boiling point of ammonia
-33.33%
Vapour compression refrigerator employs the ff cycle
Reversed Carnot
One ton of refrigeration is
The refrigeration effect to freeze 1 ton of water at 0C into ice at 0C in 24 hrs
COP of domestic refrigerator
Is more than 1
In vapor compression cycle, _______ compression of refrigerant from
saturated vapor to condenser pressure
Reversible adiabatic
In vapor compression cycle, ________rejection of heat, causing
condensation of the refrigerant
Reversible isobaric
In vapor compression cycle, _______expansion from saturated
liquid to evaporator pressure
Irreversible isenthalpic
In vapor compression cycle, _____addition of heat at constant pressure
causing evaporation to saturated vapor
Reversible
the study of the mixture of air and water
vapor
Psychrometry
properties of moist air
PSYCHROMETRIC PROPERTIES
the graphical representation of the
thermodynamics properties of moist air
PSYCHROMETRIC CHART
binary mixtures dry air and cooler vapor
Moist air
none condensing component of the mixture, mainly the
nitrogen and oxygen
Dry air
the considerable component of mixture, the water vapor
or stem which may exist in a saturated or super heated state
Vapor
vapor in the air is saturated
Saturated vapor
air containing superheated vapor
Unsaturated air
heat does not affect the temperature of the
substance but damage its state
Latent heat
the heat absorbed or given by a substance
that changes its temperature
Sensible heat
sum of latent heat and sensible heat
Total heat
the ratio of the partial pressure of water vapor in the
air to the saturation pressure corresponding to the temperature of the air
Relative Humidity
the difference between the
reading of the dry bulb and wet bulb temperature
Wet bulb
is 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
In an air-water vapor mixture, the temperature which is
the measure of the total heat of the mixture
Dry bulb
In the refrigeration system the heat absorbed in the
evaporator per pound of refrigerant passing through
a. equals the increase in enthalpy
b. equals the increase in volume
c. equals the change in temperature
d. equals the change in entropy
c. equals the change in temperature
• If the wet bulb and dry bulb reading of air temperature
are identical
a. the thermometers are in error
b. the air is saturated
c. the relative humidity is zero
d. the mixture is completely dry
c. the relative humidity is zero
Sensible heat
a. can be measured/computed with a thermometer
b. cannot be measured
c. increases with cold
d. depends on the volume
a. can be measured/computed with a thermometer
• As heat is removed from a substance it gets colder. When no more heat can be removed and the temperature cannot be lowered any further, we have
reached
a. perfect zero
b. absolute zero
c. double zero
d. cold zero
d. cold zero
In an ideal refrigeration cycle, liquid leaves the condenser and is expanded in such a manner that the enthalpy of the liquid is equal to the enthalpy of the resulting saturated mixture. This type of expansion is known as
isochoric
• The lower horizontal line of the refrigeration cycle plotted on the pressure enthalpy diagram represents
a. compression of refrigerant vapor
b. evaporation of liquid refrigerant
c. condensation of refrigerant vapor
d. metering of liquid refrigerant
d. metering of liquid refrigerant
• In which part of vapor compression system there is a change in pressure and temperature
a. Evaporator b. condenser
c. compressor d. dryer
c. compressor
What refrigerant is most commonly used for air conditioning of passenger air craft
CO2
• The amount of heat required to change the temperature of one unit weight of substance into one degree unit of temperature
specific heat
When air is saturated the wet bulb depression is
Unity
• The vertical line of refrigeration cycle plotted in the pressure enthalpy diagram represents
a. compression of refrigerant vapor
