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73 Cards in this Set
- Front
- Back
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How is a two-stage compound compressor able to sub cool the refrigerant entering the TXV that is feeding the evaporator? |
Once the refrigerant leaves the water cooled condenser there is a heat exchanger.
A txv drops the pressure to first stage discharge line pressure (intermediate stage) and WILL BE EVENTUALLY to de-superheat the first stage discharge gas BUT FIRST used to subcool the refrigerant entering the system TXV. |
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What does kryo-genic mean? |
Kryo- frost Genic - production |
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Why do we need an oil seperator on the second stage? (Thermotron) |
To keep oil out of the evaporator. It will act as an insulator. The second stage also oil thinners R-600a If it ends with -ane its probably an oil thinner. |
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What is a double direct system according to B-52? |
A double direct system consists of two completely isolated refrigerant systems, in which the evaporator of the secondary circuit cools the condenser of the primary Circuit. |
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What does the pressure relief valve look like in the thermoTron refrigerant circuit? |
Back (Definition)
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What are the sizes of the evaporator and condenser of the Low stage? What is the size of the evaporator of the high stage? (Multistage with 1 ton of cooling on the low stage evap) |
The low side “condenser” and the high side “evaporator” are the same size because they share a heat exchanger. Low stage evaporator is 1 ton Low stage condenser is 1.25 tons Hi stage evaporator is 1.25 tons. Hi stage condenser is 1.56 tons. (1.25 bigger than evap) |
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Which refrigerant is a replacement for R-502 [low temp], R-13 [CFC], and R-23 [HCFC]? |
R-508B |
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What must be attached to a charging cylinder for an ultra low? |
A pressure regulating valve |
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If the heat in the system increases, what must also happen? |
The density will go down, and the specific gravity will go up. This is why clouds float. |
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For the thermotron Why is the low stage refrigerant FIRST sent to the condenser of the high stage ( the refrigerants are kept seperate) and THEN sent to the Low stage of condenser? |
To de-superheat the gas before sending it towards the condenser. |
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Why are we bypassing the evaporator with subcooled gas |
To ensure the compressor is being cooled under low load conditions. |
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Which stage do you turn on First in a cascading system? (Thermotron) |
(1) start the high stage first to pre-cool the condenser of the low stage. (2) This will drop the low stage condensing pressure. (3) This will allow for the low stage when it starts to reject heat. (4) operator closes at goes BELOW 230 psi (self-energizing circuit) (5) when pressure climbs at start up the operator will energize the rapid firing solenoid valve. (Before the high pressure safety opens at 270 psi turning the machine off.) Pressure rises because of the high load in the box. (6) As the pressure rises, the operator will open the rapid firing solenoid and sends refrigerant to an “expansion tank” (fade out tank) increasing the volume of the high side and the discharge pressure goes down.
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Where do you put the filter dryers for the low stage of a cascade system? (There are 2 sometimes) |
(1) Right before the condenser that desuperheats the low stage refrigerant. (2) right after the Condenser (that condenses) for the low stage refrigerant. |
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According to B-52 what is considered a “High pressure switch” |
A pressure limiting device, opens on a high pressure. |
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What are the 2 functions of the operator? |
(1) turn on low stage when pressure drops (2) energize rapid firing solenoid to limit pressure rise on start up |
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In absolute pressure, if you double the volume you will… |
Halve the pressure is PSIA |
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When you are heating the thermotron why are you running the high stage compressor? |
To eliminate overshoot when they are running the induction heater. You can also run it to eliminate overshoot when you are running the humidifier They are using an epr to regulate evaporator pressure |
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On a cascade, How do you check the charge? |
You wait 24 hours and check standing pressure 100 psig @ 74F ambient on the thermotron |
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Is frosting a form of air fowling? |
Yes |
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Do you put gauges on a cascade system? |
No, critical charge and refrigerant is expensive. |
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While cascade systems are not running the low stage is 100% vapour? |
100% vapour, It would be a standing pressure of 600 psi in the charging system but it is 100 psig in the unit. R-508b Azeotropic blend Standing pressure of 600 psig Replacement for r-13,r-23, and r-503 |
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What is the name of the evap-condenser of a cascade system? |
Heat exchanger |
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How do you recover? |
Use a cold, big tank, under vaccum |
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How low do you pull down a leaking system? |
Just above atmosphere. Otherwise you will contaminate the oil |
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Should you use a nitrogen sweep on a cascade system? Should you cut or sweat? |
Cut and sweep. Refrigerant is flammable |
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For a cascade system; on the low stage…Charge downstream of the…? |
On the discharge PAST THE OIL SEPARATOR.
If you charge into the the suction it will sweep the oil out of the oil separator. If you charge on the discharge the oil will stay in the oil separator. Also charge with oil thinner on first start up (pentane, butane,… if it ends with -ane) And the oil thinners are flammable!!! |
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Auto-cascade are for long term storage at what temperature? |
150C and below |
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Auto-cascade: What is a Tertiary blend |
3 zeotropic refrigerants or more |
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Auto-cascade: Each refrigerant will fractionate at a common…. |
Suction pressure Aka… they all have the same suction line…. Oddly. |
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Auto-cascade: What type of oil seperator? |
Cyclonic oil seperator, with a float at the bottom to make sure discharge gas doesn’t recirculate. |
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Auto-cascade: The condenser is called a desuperheater/condenser because…. |
It condenses the lowest level refrigerant.
The other refrigerants will be fractioned off |
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Auto-cascade: The condenser is called a desuperheater/condenser because…. |
It condenses the lowest level refrigerant.
The other refrigerants will be fractioned off |
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Auto-cascade: The phase seperator seperates out the 404a as a liquid and the remaining refrigerant as a gas. What does the heat exchanger do with the pure liquid 404a and the remaining blend of vapor refrigerant? |
It is used to chill the remaining refrigerant before it is sent to the next phase separator. The added temperature drop will allow the 508B to seperate out.
508B is a modern refirgerant used to replace R502 [low temp], R, 13 [CFC], and our 23 [HCFC] |
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The condenser on a auto cascade is called a desuperheater/condenser because…. |
It condenses the lowest level refrigerant but it can only desuperheat the other zeotropic refrigerants at that temperature.
The other refrigerants will be fractioned off and condensed at a later heat exchanger. |
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What is the job a phase seperator is seperator out the 404a as a liquid and the remaining refrigerant as a gas. What does the heat exchanger do with the pure liquid 404a? |
It is used to chill the remaining refrigerant |
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Auto-Cascade: If the r-14 and r-508b havent filled the phase seperator with liquid where is it kept? |
In the buffer tank (fade-out vessel). the solenoid will open when the suction rises above 260 psi and fills the expansion tank. This will “increase the size of the high side” and lower the discharge pressure till the pressure is below 200 psi. Then the solenoid will close. |
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The auto cascade has two pressure sensors. One is a high limit. The other is an operator… what does it do? At 260 psi and above… (opens above 260 psi, closes at 200 psi) |
Operator Opens solenoid and fills expansion tank with buffer tank refrigerant. Expansion tank was at suction pressure. You add volume to the discharge side so the refrigerant pressure drops. (The added volume is the expansion tank because the refrigerant will stay in the expansion tank and slowly be metered into the suction line. Till the 508b and r-14 are liquid and held in the phase seperator. Then the operator will limit the discharge pressure and reduce the mass flow. In effect, controlling box temp. |
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Vapour expansion is a form of refrigeration and it occurs at the evaporator of the auto-cascade on first start up? |
Yes, it will drop the box temperature. The auto cascade will take 24 hours to drop in temperature. You are only allowed to fill the auto-cascade to 50% capacity so you can move all loads to a different freezer in the event of system failure. |
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Auto-cascade: Why is the heat exchange line bonded to the discharge line? |
To ensure 100% vapor in the buffer tank |
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How is there capacity control on the auto-cascade? |
When you bypass the refrigerant through the buffer tank this will reduce the capacity at the evaporator. Because if refrigerant bypasses the evaporator then the mass flow rate decreases and capacity decreases |
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Once per year what needs to be done to an auto-cascade? |
The unit must be turned off and completely defrosted for 24 hours |
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How full should an auto-cascade be loaded? |
You are only allowed to fill the auto-cascade to 50% capacity so you can move all loads to a different freezer in the event of system failure. |
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Auto-cascades are only sized for sensible heat and not latent heat? |
True, they are not designed to handle a large load |
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Auto cascade: The factory charge is a part number? |
Yes, if you lose some of the charge you wont know how much of which charge is lost. However the smallest particles are the first to leave. If the system is marginally low, and only some of the charge is gone, the high side and low side pressures will actually increase because the evaporator wont be able to reject heat. |
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What is R-600a used for?(auto cascade) |
An oil thinner (the flamable part) |
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If the cap tube in the phase seperator in the bottom left hand side what will happen? |
The first heat exchanger wouldnt work as effectively. |
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Auto-cascade: If the temperatures are correct up until the 3rd heat exchanger what can you assume? |
The capillary tube for this exchanger is blocked or the refrigerant used in this section has leaked out. |
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What is the equation for compression ratio is a compound compressor? |
(Discharge (abs) / suction (abs)) ^ 2 (5/1)^2 = 25:1 compression ratio The reason compound compressors exist is for large lifts in pressure. |
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What needs to happen to the intermediate stage refrigerant before it is compressed again? |
It needs to be de-superheated High pressure Refrigerant is sent through a TXV and dropped to the intermediate stage pressures and mixed with the discharged intermediate stage refrigerant. This works because the high pressure refrigerant will already be condensed and be subcooled when it mixes. Subcooled + superheated = de-superheated |
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What are the three refrigerants used in a LNG system? |
Methane, ethylene, and propane Methane has 1 carbon R-50 Ethylene has 2 carbons R-1150 Propane has 3 carbons R-290 Cool down natural gas to -161C at 4 psi for transportation. |
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What is the pump pressure on a compound compressor? |
The pump pressure will be pump discharge minus intermediate stage pressure.
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How do LNG ships lower the pressure in the vessels used for transportation? |
LNG transport ships will reduce the pressure of the carried product by removing vapour from the tops of the tanks. The vapour forms as a result of the product absorbing heat during transportation. A compressor feeds that vapour to the ships powerplant for clean burning transportation of the fuel. -161C @ 4 psi |
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How many microns do you pull down to for an auto-cascade or cascade system? |
200 microns (usually 250) |
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What does the transcritical PE chart look like? |
Back (Definition) |
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What does the transcritical PE chart look like? |
Back (Definition) |
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What refrigerant is used for the liquifaction of LNG? |
Propane R-290 |
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What does the transcritical PE chart look like? |
Back (Definition) |
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What refrigerant is used for the liquifaction of LNG? |
Propane R-290 |
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What happens to the refrigerant when it is cooled? |
Light and fluffy Density down Volume up |
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What does the transcritical PE chart look like? |
Back (Definition) |
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What refrigerant is used for the liquifaction of LNG? |
Propane R-290 |
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What happens to the refrigerant when it is cooled? |
Light and fluffy Density down Volume up |
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What type of system is an auto cascade? Cascade? |
Cascade is double direct Auto-cascade is indirect |
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What does the transcritical PE chart look like? |
Back (Definition) |
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What refrigerant is used for the liquifaction of LNG? |
Propane R-290 |
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What happens to the refrigerant when it is cooled? |
Light and fluffy Density down Volume up |
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What type of system is an auto cascade? Cascade? |
Cascade is double direct Auto-cascade is indirect |
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Should you read your ILM for this test? |
Yes |
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What is the purpose of the oil filter in a cascade system? |
To keep oil out of the evaporator |
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What is the purpose of the oil filter in a cascade system? |
To keep oil out of the evaporator |
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How much oil does the oil filter remove? |
Not 100% |
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What compressor can be used for high compression ratio? |
Screw |
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Acetylene burns are 2700F |
Brazed joint above 800F |
