refrigeration sys

what component is installed directly downstream of the TXV

evaporator coil

one refrigeration ton is equal to what heat removal rate?

12,000 btu/hr

how much heat per hours can a 5 ton refrigeration unit remove from a refrigerated space

60,000 btu/hr

if the temperature remains constants, the volume of a given mass of gas is inversely proportional to its pressure

Boyles' law

Heat motion of molecules.

Can't be created or destroyed

when a refrigeration compressor is in the off cycle, the thermal expansion valve will react in what way

It will continue to function as a result of the net balance of forces acting on the diaphragm

temperature at which air molecule movement stops

absolute zero

refrigeration systems using forced air circulation evaporators have a tendency to cause rapid dehydration of produce in chill boxes. How do you minimize dehydration?

air is circulated slowly over a large evaporator with a minimum temperature differential

in multi-box refrigeration systems, the sensing bulb of the thermostatic expansion valves used on the refrigerated boxes with elevated temperature should be located where?

before the back pressure regulating valve

term for evaporator pressure and superheat spring compression acting on thermal expansion valve

closing force

which component keeps the refrigerant circulating through the system?

compressor

in the order of direction of flow, which components are considered to separate the high pressure side of a refrigeration cycle from the low pressure side of the cycle?

compressor and expansion valve

in a typical refrigeration system, where is the temperature of the refrigerant gas at the highest?

compressor discharge

seawater or low temperature central fresh water is typically provided to a ship's stores refrigeration plant for what purpose?

condense the refrigerant gas

the only means of removing the latent heat of condensation from a refrigerant in the thermal refrigeration cycle is by performing what process

condensing refrigerant in the system condenser

what mode of heat transfer is associated with the transport of thermal energy within a body or between two bodies in direct contact

conduction

what mode of heat transfer is associated with the transport of thermal energy from one location to another by fluid in motion

convection

how can heat be transferred from one body to another?

convection, conduction, and radiation

one ton air conditioning system has what operating characteristic

cooling capacity equivalent to melting 2,000lbs of ice per day

when the sensing bulb of a thermostatic expansion valve is charged with a fluid different from the charge used in the system, what name of the charge is associated with the power element?

cross charged

the boiling point of water in an open container at sea level is 212*F, If the pressure on the open container is decreased the boiling point will ________

decrease

what does the thermal expansion valve used in a refrigeration system regulate

degree of superheat of the gas leaving the evaporator

the method most frequently used to control evaporator refrigerant flow rate in a shipboard refrigeration system

direct expansion through a TXV with constant superheat

In a refrigeration system, at what component does the refrigerant absorb the latent head of vaporization

evaporator

the component of a refrigeration system in which the refrigerant vaporizes and absorbs heat

evaporator

location of the bulb for the thermal expansion valve

evaporator coil outlet

what will remain constant during operation when a properly adjusted thermostatic expansion valve exhibits stable operation without any appreciable hunting of the valve

evaporator outlet superheat

a thermostatic expansion valve is designed to respond directly to changes in which of the following parameters?

evaporator superheat

what parameter is the thermostatic expansion valve designed to maintain constant

evaporator superheat

TXV can be adjusted why?

evaporator superheat only

in a vapor compression type refrigeration cycle, the refrigerant temperature decreases the most when passing through which system component?

expansion valve

in the order of the direction of flow, the low pressure side of a refrigeration system is considered to exist between what two components?

expansion valve and compressor

flash gas formed in the liquid line of a direct reciprocating air conditioning system may cause what condition

expansion valve pins and seats to erode

when heat is transferred from one body to another the thermal energy given up by the first body must be equal to the internal energy taken up by the second body

first law of thermodynamics

what is the equivalent tonnage of a refrigeration system rated at 48,000 btu/hr

four tons

the heat removed from the refrigerant in the condenser of a refrigeration plant

heat compression

affected most by the temperature difference between the heat source and the heat sink

heat transfer

refrigerant enters the condenser in what condition?

high pressure vapor

what would the pressure and physical state of the refrigerant residing in the system receiver

high pressure vapor on top of high pressure liquid

the receiver used in a refrigeration system performs what essential function

holds the entire refrigerant charge after system pumps down

how does heat flow

hot to cold

for a given mass of gas, the volume is inversely proportional to its pressure and directly proportional to its temperature

ideal gas law

the evaporator coil will excessively frost

if an abnormally large difference is maintained between the evaporator refrigerant temperature and the box air temperature within the refrigerated compartment, what will be the result?

Charles' law

if the pressure remains constant, the volume of a given mass of gas is directly proportional to its pressure

evaporator

in which component does the superheating of the refrigerant take place?

rather than design an infinite variety of thermostatic expansion valve sizes to accommodate different capacities for heat removal, some manufacturers use a few standard valve body sizes in conjunction with what other feature

internal needle valve orifices of various sizes to accommodate different heat removal capacities

a constant hissing sound at the thermal expansion valve will always indicate what condition?

lack of refrigerant

what term is defined as the amount of heat required to convert a unit mass of a substance from a liquid to a vapor at constant temperature and pressure

latent heat of vaporization

in a typical refrigeration system, refrigerant leaving the receiver will then flow to what system component

liquid line strainer

if a thermostatic expansion valve is adjusted for too low a superheat setting, what will be the result

liquid may flood back to the compressor

refrigerant entering the compressor of a refrigeration system should be in which of the following conditions?

low pressure vapor

when multiple refrigeration evaporators are served by the same compressor and operate at different temperatures, what is true concerning the pressure of the coldest evaporator?

lower than the pressure in the warmest evaporator

what is the primary purpose f the thermostatic expansion valve as used in most refrigeration plants

maintain a constant degree of superheat at the evaporator coil outlet

what is the primary purpose of the thermostatic expansion valve as used in most refrigeration plants

maintain a constant degree of superheat at the evaporator coil outlet

heat transfer rates are directly proportional to the difference in fluid densities which, in turn, is directly proportional to the temperature gradient

natural convection

bulb pressure acting on thermal expansion valve is the

opening force

Fahrenheit absolute scale

rankine

what is the greatest effect of excess frost accumulation on evaporator coils in a refrigeration system

reduces the efficiency of the plant

the temperature of the refrigerant in the evaporator coil depends mostly upon what factor

refrigerant pressure in the evaporator

what is true concerning a typical shipboard multi-coil refrigeration system

refrigerant temperature in an evaporator is directly related to refrigerant pressure

one function of the thermal expansion valve used in a refrigerant system

regulate the amount of refrigerant flow to the evaporator coil

term applied primarily to the fresh vegetables cargo

respiratory heat

which condition what cause the thermal expansion valve to further open in a refrigeration system

rise in temperature at the evaporator outlet

zinc plates commonly found in refrigeration systems and used as sacrificial anodes are located where?

saltwater side of the condenser

the thermal bulb for a thermal expansion valve used in a reciprocating air conditioning system is usually charged with what substance

same refrigerant as the system

refrigerant leaving the metering device in a refrigeration system is a

saturated liquid/vapor mixture

zinc rods are installed in the refrigeration system in what location

seawater cooled condenser heads

when heat is transferred from one body to another, the direction of heat flow is uni-directional from the relatively hot body to the relatively cold body

second law of thermodynamics

transmits the bulb pressure (proportional to the coil temperature) to the thermal expansion valve diaphragm

sensing line

what term is identified as the quantity of heat necessary to raise the temperature of a unit mass of a substance one degree

specific heat

in a refrigeration plant, what is one vital purpose of the receiver?

store the refrigerant charge

the receiver used in a refrigeration systems performs what function

stores liquid refrigerant and acts as a surge tank to compensate for changes in system load

under normal conditions, the refrigerant leaves the condenser in an operating refrigeration system as a _________

sub-cooled liquid

amount of heat a substance contains and applies to vapors

superheat

the refrigerant gas returning t the compressor should be in what condition?

superheated

the refrigerant returning to the compressor should be ______

superheated

the low pressure refrigerant leaves the evaporator of a refrigerant system in what condition?

superheated vapor

the refrigerant leaves the evaporator of a refrigeration system as a low pressure

superheated vapor

the refrigerant leaves the evaporator of a refrigeration system as a low pressure _____

superheated vapor

the level of heat or heat intensity

temperature

besides the evaporator pressure, the thermal expansion valve reacts directly to changes in what parameter

temperature of the evaporator coil outlet

in a refrigeration system, the pressure within the power element of a thermostatic expansion valve depends directly upon what factor

temperature of the evaporator coil outlet

In a dry-type direct expansion refrigeration evaporator, what is true concerning the evaporator coils?

the coils are surrounded on the outside by air

a TXV is properly controlling evaporator superheat. Adjusting this valve to lower the evaporator superheat setting will results in what?

the evaporator feed will increase

radiation is

the mode of heat transfer that is associated with the transport of thermal energy through a transparent medium by means of electro-magnetic energy in the infrared spectrum

the actual position of the needle valve is dependent upon what

the net force of the evaporator pressure and the superheat adjusting spring

power is

the rate of doing work

in order for heat transfer to take place between two substances, what essential condition must exist?

the two substances must be different temperatures

In a refrigeration system, the amount of superheat absorbed by the refrigerant flowing through the evaporator coil is adjusted at what device

thermal expansion valve

constant superheat is maintained at the evaporator coil outlet of a refrigeration system or until by the action of what device

thermal expansion valve

superheated vapor

under normal conditions, the refrigerant enters the compressor in an operation refrigeration system in what condition?

reduce the possibility of moisture laden warm air from outside the refrigerated space from entering the insulation

vapor barrier seals

in the normal operation of a refrigeration system, where the refrigeration compressor cycles off, the thermal expansion valve will react in what manner

will respond according to operating forces acting on the valve