F-Gas English Low GWP
Všetky otázky
HFC | Flammable | CO₂ | NH₃
Ľahké otázky |
Stredne ťažké otázky |
Ťažké otázky
1
Ťažká
What is the main difference between a dry-expansion and a flooded evaporator?
| A dry-expansion evaporator needs no expansion valve, a flooded one does |
| A dry-expansion evaporator is filled with liquid, a flooded one with vapour |
| A dry-expansion evaporator always has a lower pressure than a flooded one |
| In a dry-expansion evaporator the refrigerant completely evaporates and is superheated in the evaporator; in a flooded one part of the refrigerant remains liquid (incomplete evaporation, no superheat) |
2
Ťažká
What is the typical pressure in the evaporator of an R717 deep-freeze system (below −40 °C)?
| Below atmospheric (approx. 0.7 bar abs at −40 °C) |
| Positive pressure of 5–10 bar |
| Atmospheric pressure, approx. 1 bar abs |
| Positive pressure of 10–20 bar |
3
Ťažká
How is oil managed in R717 systems?
| Oil can be mixed with any refrigerant |
| Oil has no effect on system operation |
| Oil collecting at the lowest points of vessels is regularly checked and drained, because it impairs heat transfer |
| Oil requires no monitoring |
4
Ťažká
What should be done with contaminated R717?
| Continue to use it without restriction |
| Release it into the atmosphere |
| Dilute it with water and reuse it |
| Purify it or send it for disposal in accordance with regulations |
5
Ťažká
What should be done if an NH₃ leak is detected?
| Increase the pressure in the system |
| Carry on working wearing a dust mask |
| Evacuate people immediately and raise the alarm; stop the leak only if it is safe to do so and with suitable PPE (respiratory protection) |
| Carry on working with the room door open |
6
Ťažká
What role do scrubbers play in NH₃ systems?
| Neutralise ammonia through absorption in a liquid (e.g. water) |
| They store the refrigerant |
| They increase the pressure in the system |
| They are used to measure temperature |
7
Ťažká
How should the system be prepared before filling with R717?
| Simply start it up |
| There is no need to check it |
| Check for leaks, remove air and moisture, and create a vacuum |
| The pressure must be increased above the standard level |
8
Ťažká
What are the transport requirements for R717?
| It can be carried without labelling |
| It must be carried in suitable, labelled packagings in accordance with ADR (UN 1005, class 2, code 2TC) |
| It can be carried in open containers |
| Transport is not regulated |
9
Ťažká
Which statement best describes the behaviour of R717 and mineral compressor oil?
| R717 mixes very well with the oil, which easily returns to the compressor |
| R717 does not mix with the oil; the oil collects on the high-pressure side above the R717 |
| An oil return line cannot be used in R717 systems because the oil is too hot |
| R717 does not mix with the oil; the oil, being heavier than liquid NH₃, collects beneath it at the lowest points (mainly on the low-pressure side) |
10
Ťažká
Which refrigerant can be detected with phenolphthalein paper?
| R1270 |
| R744 |
| R1234ze(E) |
| R717 |
11
Ťažká
Which system may require manual oil recovery?
| An R717 system |
| Supercritical ‘booster’ system using R744 |
| Secondary system using R744 |
| R744 cascade system |
12
Ťažká
Which refrigerant is lighter than air?
| R1270 |
| R1234ze(E) |
| R717 |
| R744 |
13
Ťažká
R717 is highly corrosive to:
| copper (and its alloys) |
| titanium |
| aluminium |
| stainless steel |
14
Ťažká
What is the recommended pre-alarm level for fixed leak detection systems for R717?
| 500 ppm |
| 5,000 ppm |
| 500,000 ppm |
| 50,000 ppm |
15
Ťažká
Why are compressors with a separate motor (open type) mostly used in R717 systems?
| Because they are cheaper |
| To lower the condensing pressure |
| Because NH₃ attacks copper motor windings, so hermetic compressors with conventional windings are not used |
| To increase the refrigerant charge |
16
Ťažká
Which type of compressor is most commonly used in large ammonia systems?
| Hermetic scroll |
| Rotary vane compressor |
| Diaphragm compressor |
| A reciprocating or screw compressor |
17
Ťažká
How is the capacity of a piston compressor regulated in NH₃ systems?
| By increasing the condensing pressure |
| By unloading the cylinders or changing the rotational speed |
| Solely by adjusting the oil volume |
| By reducing the refrigerant charge |
18
Ťažká
How is the capacity of a screw compressor most commonly controlled?
| By using a slide valve |
| By adjusting the oil level |
| By changing the type of oil |
| By closing the suction valve |
19
Ťažká
When is two-stage compression used in NH₃ systems?
| Only in small systems |
| Only with water-cooled condensers |
| At low evaporating temperatures (pressures) and high pressure ratios |
| At small temperature differences |
20
Ťažká
What is the advantage of two-stage compression over single-stage compression?
| Lower efficiency |
| No need for a separator |
| Higher energy consumption |
| Higher efficiency and lower discharge temperature |
21
Ťažká
How does an evaporative condenser used in NH₃ systems work?
| It does not require a water supply |
| It transfers heat only to the air |
| Operates without a fan |
| It utilises the evaporation of water to increase cooling efficiency |
22
Ťažká
What is the function of the liquid separator in an NH₃ system?
| Increases the discharge temperature |
| Regulates the condensing pressure |
| It separates oil from the refrigerant |
| It prevents liquid from entering the compressor |
23
Ťažká
What is the purpose of monitoring the liquid level in the separator?
| To increase the oil volume |
| To control the condenser fan |
| To maintain the correct refrigerant level and prevent the compressor from flooding |
| To reduce the condensing temperature |
24
Ťažká
What is the role of the float switch in NH₃ systems?
| It regulates the condensation temperature |
| It is used to detect leaks |
| It monitors the liquid level in the tank or separator |
| It controls the fan’s operation |
25
Ťažká
What is a thermosyphon in NH₃ systems?
| A defrosting device |
| A type of safety valve |
| A system with gravity-driven (natural) circulation of liquid refrigerant caused by density differences, used e.g. for screw compressor oil cooling |
| An oil circulation pump |
26
Ťažká
Why are oils that are immiscible with the refrigerant used in NH₃ systems?
| Because NH₃ does not mix with most compressor oils |
| To reduce the pressure |
| Because the oil mixes only with water |
| To increase the amount of refrigerant |
27
Ťažká
What is the main function of an oil separator in NH₃ systems?
| Removing moisture from the system |
| To lower the condensation temperature |
| To separate the oil from the refrigerant and return the oil to the compressor |
| To increase fan efficiency |
28
Ťažká
In which NH₃ system does the refrigerant evaporate completely with superheat in the evaporator, fed by an expansion valve?
| A pumped liquid-recirculation system |
| A direct-expansion (DX) system |
| A glycol system |
| An indirect system |
29
Ťažká
What is the characteristic feature of a flooded evaporator system?
| No separator is used |
| No level control is required |
| The evaporator contains a large amount of liquid, which improves heat transfer |
| The evaporator is filled exclusively with vapour |
30
Ťažká
What is the main difference between a direct and an indirect system?
| In an indirect system, no compressor is used |
| In an indirect system, NH₃ cools an intermediate medium (e.g. glycol), which in turn cools the load |
| In an indirect system, NH₃ flows directly into the space being cooled |
| In a direct system, there is no evaporator |