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RETA INDUSTRIAL REFRIGERATION EXAM
| 2 DIFFERENT EXAMS | ALL QUESTIONS
AND CORRECT ANSWERS | GRADED A+ |
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RETA INDUSTRIAL REFRIGERATION (FIRST EXAM)
When servicing a DX air unit? (pg. 4-12) A) It is acceptable to use the TXV as an isolation valve as the warm temperature will result in a complete closing of the valve B) A separate isolation valve must always be used to isolate the coil C) The TXV can be used to isolate the coil if the superheat adjustment is turned completely in to the "manual off" position D) The TXV can be used to isolate the coil if the superheat adjustment is turned completely out to the "manual off" position ------CORRECT ANSWER---------------B) A separate isolation valve must always be used to isolate the coil Which of the following is a typical function of a low-side vessel? (pg. 4-19) A) Oil cooling B) Phase separation C) Thermosyphon refrigerant storage D) Sub-cooling liquid for low-side use ------CORRECT ANSWER--------------- B) Phase separation If the power element of a TXV lost its charge...? A) The evaporator would starve B) The evaporator would hunt C) There would be low superheat at the coil outlet D) The evaporator would flood ------CORRECT ANSWER---------------A) The evaporator would starve
Hand expansion valves are? (pg. 4-12) A) Seldom used in new systems B) Only used to feed gravity flooded evaporators C) Not used in a series with another feed control device D) Commonly used in a series with another feed control device ------ CORRECT ANSWER---------------D) Commonly used in a series with another feed control device The thermostatic expansion valve is opened by forces coming from? (pg. 4-
A) Evaporator pressure only B) Evaporator temperature only C) Compressor pressure only D) Sensing bulb pressure ------CORRECT ANSWER---------------D) Sensing bulb pressure A hand expansion valve can control the flow of refrigerant into an evaporator better than a typical stop valve because? (pg. 4-4) A) It is larger than the liquid line pipe size feeding it B) It has an adjustable orifice designed to control flow C) It is made of special alloy metal that expands and contracts with temperature change D) Pointers can be attached to the hand wheel ------CORRECT ANSWER-- -------------B) It has an adjustable orifice designed to control flow Where may hand expansion valves be found in modern industrial refrigeration systems? (pg. 4-28) A) They are not used B) They are commonly used as the only valve feeding the evaporator C) They are usually not used in series with another feed device
B) They are commonly used on dry expansion evaporators C) They are commonly used on pumped overfeed evaporators D) They are commonly used in a bypass around an automatic liquid feed --- ---CORRECT ANSWER---------------B) They are commonly used on dry expansion evaporators The advantage of a float valve liquid make-up device is? (pg. 4-28) A) 120 VAC control power B) Low cost C) Their design allows easy maintenance and or replacement D) Proportional responsiveness to changes in liquid level ------CORRECT ANSWER---------------D) Proportional responsiveness to changes in liquid level The float switch maintains the liquid level by? (pg. 4-28) A) Opening and closing the expansion valve B) Opening and closing the liquid solenoid valve C) Opening and closing the hot gas valve D) Opening and closing the float valve ------CORRECT ANSWER------------- --B) Opening and closing the liquid solenoid valve Heating the bulb of a Sporlan Level Master thermostatic expansion valve causes? (pg. 4-33/34) A) Increased liquid flow B) Increased superheat C) Decreased liquid flow D) Decreased bulb pressure ------CORRECT ANSWER---------------A) Increased liquid flow Why are hand expansion valves used in series with solenoid valves on a gravity flooded evaporator? A) To protect the hand expansion valve from erosion damage
B) Hand expansion valves are required to set evaporator pressure C) To protect the solenoid valve from erosion damage D) To reduce the operating pressure of the solenoid valve ------CORRECT ANSWER---------------C) To protect the solenoid valve from erosion damage Hand expansion valves are used in a series with solenoid valves to? A) Control evaporator pressure B) Regulate flow of the refrigerant C) Regulate the superheat generated in the evaporator D) To protect the hand expansion valve from erosion damage ------ CORRECT ANSWER---------------B) Regulate flow of the refrigerant Why is a DX coil considered dry expansion? (pg. 5-1/2) A) Because it has no liquid in it B) Because the condition of the refrigerant leaving the coil is a '"dry" vapor C) Because they always operate in a dry environment D) Because they do not form condensation on their surface and therefore do not dehumidify the air passing over them ------CORRECT ANSWER------ ---------B) Because the condition of the refrigerant leaving the coil is a '"dry" vapor In steady state operation, approximately how far through the coil circuit path does liquid refrigerant travel in a properly adjusted DX coil? (pg. 5-1) A) 25% B) 50% C) 75% D) 100% ------CORRECT ANSWER---------------C) 75% Where does the flash gas go after the expansion valve in a DX coil system? (pg. 5-2) A) Through the coil with the liquid refrigerant B) Around the coil straight to the suction line
A) Flash gas flows through the coil B) It requires a pump to operate C) It must be located near a surge drum D) The typical expansion device used for DX coils must be manually adjusted to keep up with changing load ------CORRECT ANSWER------------ ---A) Flash gas flows through the coil As defined in the text, liquid slugs (in DX coils) result from? (pg. 5-4) A) High velocity vapor pushing liquid ahead of it B) A TXV closing abruptly C) A compressor unloading rapidly D) Oil accumulating in the bottom of a coil ------CORRECT ANSWER--------- ------A) High velocity vapor pushing liquid ahead of it Which of the following is NOT true about suction line accumulators in a plant? (pg. 5-10) A) They may be emptied by allowing the liquid to evaporate from the accumulator B) They may be emptied by automatic pumps C) They may be emptied automatically with a transfer system D) They are intended to maintain a constant liquid level and therefore do not need to be emptied ------CORRECT ANSWER---------------D) They are intended to maintain a constant liquid level and therefore do not need to be emptied How much liquid (by volume) is in a properly operating dry expansion evaporator? (pg. 5-1) A) There is no liquid in a dry expansion evaporator, it is all vapor B) These evaporators average about 1/4 full of liquid refrigerant by volume during operation C) These evaporators average about 1/2 full of liquid refrigerant by volume during operation D) These evaporators average about 3/4 full of liquid refrigerant by volume during operation ------CORRECT ANSWER---------------B) These
evaporators average about 1/4 full of liquid refrigerant by volume during operation As defined in the text, what other names are dry expansion evaporators called? (pg. 5-1/2) A) DX coils or direct expansion evaporators B) Air coils or DX coils C) Direct expansion evaporators or flash gas coils D) Suction evaporators or flash gas coils ------CORRECT ANSWER---------- -----A) DX coils or direct expansion evaporators Which statement is NOT true regarding the refrigerant passing through a dry expansion evaporator? A) It is completely changed to a vapor before leaving the coil to enter the compressor B) Part of the liquid vaporizes instantly when leaving the expansion valve C) It "boils" D) It is sub-cooled as it enters the evaporator ------CORRECT ANSWER---- -----------D) It is sub-cooled as it enters the evaporator Which of the following does NOT happen when the cooling load is increased on a system using a dry expansion evaporator? A) The boiling rate increases B) The rate at which vapor is produced increases C) The compressor will have to move more vapor or the pressure in the evaporator will rise D) The TXV will respond by reducing the refrigerant flow to the coil ------ CORRECT ANSWER---------------D) The TXV will respond by reducing the refrigerant flow to the coil Which of the following factors listed below does not affect heat transfer? (pg. 1-2)
Which statement is true? (pg. 1-3) A) The higher the 'k' factor, the greater the thermal conductivity B) The lower the 'k' factor, the greater the thermal conductivity C) The higher the 'k' factor, the lower the thermal conductivity D) The 'k' factor is not associated with thermal conductivity ------CORRECT ANSWER---------------A) The higher the 'k' factor, the greater the thermal conductivity Optimum 'U' factor for the given material that the heat exchanger is made of results when? (pg. 1-7/8) A) There is no impeding substance such as ice, dirt, or oil on the surfaces of the heat exchanger tubes B) Maximum airflow across the evaporator is achieved C) The system is operating with the design recirculation low D) The system is maintaining temperature ------CORRECT ANSWER-------- -------A) There is no impeding substance such as ice, dirt, or oil on the surfaces of the heat exchanger tubes When air flow is decreased across a heat exchange surface, cooling capacity is? (pg. 1-10) A) Reduced B) Increased C) Not changed because area is not changed D) Not changed because evaporator temperature is not changed ------ CORRECT ANSWER---------------A) Reduced Centrifugal fans have an advantage over propeller fans in that they ______________ than prop fans? (pg. 1-12) A) Require less physical space B) Consume more hp per CFM of air moved C) Are quieter D) Have fewer components to maintain ------CORRECT ANSWER------------ ---C) Are quieter
The operating engineer? (pg. 1-7) A) Cannot change the 'k' factor of the metal but has some control of the overall 'U' factor for the evaporator as a unit B) Can increase 'k' factor by increasing the air velocity over the evaporator and has some control of the overall 'U' factor for the evaporator as a unit C) Should allow frost to collect on the evaporator increase 'k' factor D) Can increase 'k' factor by starting another compressor ------CORRECT ANSWER---------------A) Cannot change the 'k' factor of the metal but has some control of the overall 'U' factor for the evaporator as a unit The limiting factor of an evaporator's capacity that the operator cannot control is? (pg. 1-7) A) Suction Temperature B) Suction Pressure C) Evaporator Size D) Refrigerant Liquid Feed Flow ------CORRECT ANSWER---------------C) Evaporator Size The best way to keep an evaporator from being affected by oil build-up is to? (pg. 1-8) A) Operate the system at the correct evaporator temperature B) Periodically remove oil from the oil collection points C) Set hot gas defrost cycle for a minimum of 30 minutes D) Increase air flow across the evaporators ------CORRECT ANSWER------- --------B) Periodically remove oil from the oil collection points The effectiveness of a heat transfer surface depends on several factors. One factor the operator has control over is? (pg. 1-8) A) Evaporator surface area B) Material the evaporator is made of C) Type of fans used
C) The capacity of the evaporator is not changed D) The capacity of the evaporator is increased by 50% ------CORRECT ANSWER---------------C) The capacity of the evaporator is not changed Damaged insulation on the suction line in an ammonia refrigeration system will? (pg. 1-14) A) Not change the efficiency of the system because suction pressure will not change B) Cause efficiency loss and potential damage to the suction line C) Look bad but will not cause any major problems D) Cause an efficiency loss but will not cause any other problems ------ CORRECT ANSWER---------------B) Cause efficiency loss and potential damage to the suction line Enthalpy is? (pg. 2-2) A) A measure of total energy (heat content) per pound of refrigerant measured in BTU's B) The net heat absorbing capacity of the refrigerant after the point of expansion C) The amount of cooling effect that can be obtained from a refrigeration system D) Heat that cannot be measured through a change in temperature ------ CORRECT ANSWER---------------A) A measure of total energy (heat content) per pound of refrigerant measured in BTU's The enthalpy diagram? (pg. 2-6) A) Illustrates the changes of condition and heat content of a pound of refrigerant at different points of the refrigeration cycle B) Illustrates the total heat transfer capacity of the system from evaporators through condensers in tons of refrigeration C) Utilizes two scales, pressure and tons of refrigeration D) Does not take into account the effect of flash gas ------CORRECT ANSWER---------------A) Illustrates the changes of condition and heat content of a pound of refrigerant at different points of the refrigeration cycle
The enthalpy diagram has three regions of refrigerant condition which are? (pg. 2-10) A) Solid, Liquid and Gas B) Subcooled Liquid, SAT Liquid and Vapor, and Superheated Vapor C) Hot, Medium, and Cold D) Flash Gas, Subcooled Liquid, Subcooled Liquid and Flash Gas ------ CORRECT ANSWER---------------B) Subcooled Liquid, SAT Liquid and Vapor, and Superheated Vapor The pressure scale on an enthalpy diagram typically used in the U.S. is expressed in? (pg. 2-8) A) Kilopascals B) PSIG C) PSIA D) Newtons ------CORRECT ANSWER---------------C) PSIA In a refrigeration system (at normal refrigeration pressures), how does the heat content of a pound of saturated vapor compare to the heat content of a pound of saturated liquid? (pg. 2-10) A) The heat quantity in a pound of saturated vapor is greater than the heat quantity in a pound of saturated liquid at the same pressure B) The heat quantity in a pound of saturated vapor is less than the heat quantity in a pound of saturated liquid at the same pressure C) The heat quantity in a pound of saturated vapor is equal to the heat quantity in a pound of saturated liquid at the same pressure D) It is not possible to measure heat content in a pound of saturated vapor ------CORRECT ANSWER---------------A) The heat quantity in a pound of saturated vapor is greater than the heat quantity in a pound of saturated liquid at the same pressure
The boundary line that separates the saturated mixture region and the superheated vapor region? (pg. 2-10) A) Is 100% saturated liquid B) Is 100% saturated vapor C) Represents a theoretical condition not achievable in a real system D) Represents the critical pressure of the refrigerant ------CORRECT ANSWER---------------B) Is 100% saturated vapor A simple refrigeration cycle plotted on the enthalpy diagram illustrates why a condenser must reject more heat than just the heat absorbed in the evaporator because of? (pg. 2-17) A) Subcooling B) Heat of Compression C) Saturation D) Evaporation ------CORRECT ANSWER---------------B) Heat of Compression A vertical change (change of pressure) in the subcooled liquid region or in the saturated mixture region __________ the enthalpy of the refrigerant at that point? (pg. 2-11) A) Increases B) Decreases C) Does Not Change D) Multiplies ------CORRECT ANSWER---------------C) Does Not Change Superheat enters the system at? A) The condenser, high-pressure receiver, and the evaporator B) The liquid line, evaporator, and condenser C) The evaporator, suction lines, and compressor D) The pump accumulator package ------CORRECT ANSWER--------------- C) The evaporator, suction lines, and compressor
In a two-stage system, subcooled liquid entering the evaporator generally enhances the performance of the system because? (pg. 2-32) A) It really makes no difference B) There is less flash gas formed for the low-stage compressor to handle C) Subcooling the liquid causes the molecules to be spaced further apart which gives them a running head start toward evaporating into liquid along with the flash gas D) Subcooling of liquid entering the evaporator is never an advantage, it always reduces the performance of the evaporator ------CORRECT ANSWER---------------B) There is less flash gas formed for the low-stage compressor to handle The single-stage reciprocating ammonia compressor is operating at a suction temperature of 10°F from a freezer unit with an evaporating temperature of 0°F. The condensing temperature is 95°F. What is the theoretical discharge temperature? A) 210°F B) 350°F C) 260°F D) 310°F ------CORRECT ANSWER--------------- What is the compression ratio for the conditions above? A) 11 : 1 B) 6.4 : 1 C) 30 : D) 34 : 1 ------CORRECT ANSWER---------------95°F = 195.35 PSIA, 0°F = 30.32 PSIA 195.35 PSIA / 30.32 PSI = 6. B) 6.4 : 1 What can be done to reduce the discharge temperature? A) Drop the suction pressure of the evaporator B) Increase suction superheat C) Decrease suction superheat
C) An indication of the sensible heat content of the air D) An indication of the humidity in the air ------CORRECT ANSWER---------- -----C) An indication of the sensible heat content of the air A high relative humidity will? (pg. 3-9/10) A) Increase evaporative condenser capacity because there is more moisture in the air B) Increase the infiltration load on a refrigeration system C) Increase the time between evaporator defrosts D) Decrease evaporative condenser capacity because there is less moisture in the air ------CORRECT ANSWER---------------B) Increase the infiltration load on a refrigeration system Wet bulb temperatures? (pg. 3-6) A) Require increased evaporative condenser capacity if they are high B) Require increased evaporative condenser capacity if they are low C) Cannot be used to determine the dew point D) Can be determined without using a thermometer ------CORRECT ANSWER---------------A) Require increased evaporative condenser capacity if they are high Cold air? (pg. 3-10) A) Is lighter than warm air B) Is heavier than warm air C) Holds more moisture than warm air D) Increases pressure in a freeze ------CORRECT ANSWER---------------B) Is heavier than warm air If the dry bulb temperature is 80°F and the RH is 30%, what is the wet bulb temperature? (pg. 3-12) A) 80°F B) 60°F
C) 70°F
D) 68°F ------CORRECT ANSWER---------------B) 60°F
If the RH is 100% and the wet bulb temperature is 70°F, what is the dry bulb temperature? (pg. 3-12) A) 84°F B) 60°F C) 70°F D) 65°F ------CORRECT ANSWER---------------C) 70°F If the dry bulb temperature is 75°F and the RH is 35%, what is the enthalpy per pound of dry air? (pg. 3-12) A) 8 BTU/pound B) 25 BTU/pound C) 2.5BTU/pound D) 46 BTU/pound ------CORRECT ANSWER---------------B) 25 BTU/pound If the dry bulb temperature is 72°F and the wet bulb temperature is 65°F, what is the relative humidity? (pg. 3-12) A) 61% B) 65% C) 70% D) 30% ------CORRECT ANSWER---------------C) 70% If the dry bulb temperature is 75°F and the wet bulb temperature is 70°F, what is the volume of a pound of the air? (pg. 3-12) A) 14.2 cubic feet B) 14.0 cubic feet C) 13.8 cubic feet D) 13.6 cubic feet ------CORRECT ANSWER---------------C) 13.8 cubic feet
