Mississippi Refrigeration Examination

In a vapor-compression refrigeration cycle, the four essential components in flow order starting at the compressor discharge are the:

• AEvaporator, compressor, expansion device, and condenser
• BCondenser, expansion device, evaporator, and compressor suction
• CExpansion device, condenser, receiver, and evaporator
• DOil separator, evaporator, condenser, and compressor

The compressor in a refrigeration system primarily:

• ARejects heat from the refrigerant to the outdoor air or condenser water
• BMeters liquid refrigerant into the evaporator
• CRaises refrigerant vapor pressure and temperature so heat can be rejected
• DSeparates oil from liquid refrigerant in the receiver

One ton of refrigeration is defined as a heat-removal rate of:

• A1,000 Btu per hour
• B144,000 Btu per hour
• C200 Btu per hour
• D12,000 Btu per hour

Evaporator superheat is best defined as:

• AThe number of degrees a refrigerant vapor is above its saturation temperature at the meas…
• BThe number of degrees a refrigerant liquid is below its saturation temperature at the mea…
• CThe temperature rise of condenser water through the tower
• DThe difference between compressor discharge temperature and outdoor dry-bulb temperature

Liquid-line subcooling is best defined as:

• ASuction-vapor temperature minus evaporator saturation temperature
• BThe number of degrees liquid refrigerant is below its saturation temperature at the measu…
• CCondenser saturation temperature minus outdoor wet-bulb temperature
• DThe temperature drop across the expansion valve orifice

Most of the useful cooling in a direct-expansion evaporator comes from:

• ASensible heating of superheated vapor after the last droplet boils
• BSensible cooling of subcooled liquid before it enters the coil
• CLatent heat absorbed as saturated liquid vaporizes at evaporating pressure
• DHeat generated by compressor motor windings

For a pure refrigerant, saturation temperature is determined by:

• AThe mass of refrigerant in the receiver only
• BThe pressure of the two-phase mixture
• COutdoor dry-bulb temperature alone
• DCompressor motor horsepower

Ozone depletion potential (ODP) of a refrigerant is associated primarily with:

• AFluorine content
• BChlorine or bromine content
• CMolecular weight
• DCritical pressure

Flash gas at the expansion device is caused by:

• AThe isenthalpic pressure drop that vaporizes part of the liquid to cool the remaining liq…
• BOil logging in the evaporator
• CA dirty condenser coil only
• DExcessive evaporator superheat

Heat is absorbed from the refrigerated space primarily in the:

• ACondenser
• BCompressor discharge line
• CEvaporator
• DLiquid receiver

On a pressure-enthalpy (P-h) diagram, the expansion process through a TXV or orifice is drawn as:

• AA horizontal line of constant pressure
• BA vertical line of constant enthalpy
• CA line of constant entropy sloping up and to the right
• DA horizontal line in the superheated-vapor region

On a P-h diagram, evaporation is represented by:

• AA vertical line at constant enthalpy under the dome
• BA horizontal line of constant pressure moving left to right through the two-phase region
• CA line moving up and to the right in the subcooled-liquid region
• DA vertical line in the superheated region

A technician measures 68 psig suction pressure on an R-22 system. The P-T chart lists 40 F saturation at 68.5 psig. The suction-line temperature at the evaporator outlet is 52 F. Evaporator superheat is:

• A8 F
• B28 F
• C40 F
• D12 F

Liquid-line pressure is 226 psig on an R-22 plant. Saturation temperature at 226 psig is 105 F. A well-insulated liquid-line thermometer reads 92 F. Liquid subcooling is:

• A8 F
• B13 F
• C21 F
• D105 F

A compressor has a suction pressure of 20 psig and a discharge pressure of 180 psig. Using 14.7 psi atmospheric pressure, the compression ratio is closest to:

• A3.2
• B9.0
• C12.2
• D5.6

Temperature glide in a zeotropic blend such as R-407C or R-448A means:

• AThe blend boils and condenses at a single fixed temperature at a given pressure
• BBubble-point and dew-point temperatures differ, so temperature changes during isobaric ph…
• CThe oil viscosity increases linearly with temperature
• DThe blend cannot be charged as a liquid

Industrial plants use two-stage (compound) compression primarily when:

• AThe condensing temperature is below 70 F
• BA single-stage compression ratio would be excessive, typically on low-temperature ammonia…
• COnly air-cooled condensers are available
• DThe evaporator is a direct-expansion coil above 40 F

Anhydrous ammonia (R-717) is widely used in industrial refrigeration because it has:

• AZero ODP, very low GWP, and a high latent heat, despite being toxic and mildly flammable…
• BASHRAE 34 safety group A1 and a very high GWP
• CA condensing pressure similar to R-410A at ordinary temperatures
• DNo odor, so leaks cannot be detected without instruments

Carbon dioxide (R-744) used as a refrigerant is characterized by:

• ALow operating pressures and a high critical temperature
• BASHRAE 34 group A1, very high operating pressures, and a low critical temperature that of…
• CSafety group B2L and use of copper ACR tubing exclusively
• DZero pressure at 32 F

ASHRAE 34 class 2L refrigerants such as R-32 and R-1234yf are best described as:

• AHighly flammable hydrocarbons equivalent to propane (A3)
• BLower-flammability refrigerants with a burning velocity at or below 10 cm/s
• CHigh-toxicity refrigerants that cannot be used in occupied spaces under any code
• DOzone-depleting CFCs banned from new equipment

Which list correctly ranks typical 100-year GWP from highest to lowest?

• AR-717 ammonia, R-744 CO2, R-404A
• BR-404A, R-134a, R-1234yf, R-717
• CR-1234yf, R-134a, R-404A, R-717
• DR-744, R-32, R-404A, R-12

A system must deliver 20 tons. The refrigerating effect from the P-h diagram is 80 Btu/lb. Required refrigerant mass flow is:

• A3.0 lb/min
• B8.0 lb/min
• C50.0 lb/min
• D200.0 lb/min

In a pumped liquid-recirculation (overfeed) ammonia plant, a 4:1 recirculation ratio means:

• AFour compressors serve each evaporator
• BFour pounds of liquid are supplied to the evaporator for each pound vaporized
• CThe liquid pump runs at four times compressor speed
• DDischarge pressure is four times suction pressure

Polyolester (POE) lubricant is specified with most HFC and HFO systems because:

• APOE is immiscible with HFCs, which improves oil return
• BPOE is miscible with HFCs/HFOs, supporting oil return that mineral oil cannot provide
• CPOE is the only oil that can be used with ammonia
• DPOE never absorbs moisture

The critical point on a P-h diagram is the top of the saturation dome. Above the critical temperature a refrigerant:

• ACannot exist as a distinct liquid-vapor mixture and cannot be condensed by pressure alone
• BAlways remains a subcooled liquid regardless of pressure
• CHas zero enthalpy
• DMust be ammonia

Saturated liquid enthalpy entering a TXV is 40 Btu/lb. Enthalpy of saturated liquid at evaporator pressure is 20 Btu/lb, and latent heat at that pressure is 80 Btu/lb. The flash-gas fraction after expansion is:

• A10 percent
• B25 percent
• C40 percent
• D50 percent

From a P-h diagram: evaporator outlet h1 = 110 Btu/lb, compressor discharge h2 = 130 Btu/lb, and condenser outlet h3 = 40 Btu/lb. Assuming isenthalpic expansion, the cycle COP is:

• A2.0
• B3.5
• C4.5
• D7.0

A compressor pumps 6.0 lb/min of refrigerant. Enthalpies are h1 = 108 Btu/lb at the suction and h4 = 38 Btu/lb at the evaporator inlet. Refrigeration capacity is:

• A1.8 tons
• B2.1 tons
• C3.5 tons
• D6.0 tons

For an ideal two-stage plant, a common first estimate of intermediate pressure is the geometric mean of the suction and discharge absolute pressures. If suction is 10.3 psia and discharge is 195.7 psia, the estimated intermediate pressure is closest to:

• A22 psia
• B103 psia
• C186 psia
• D45 psia

Using h2 = 130 Btu/lb at compressor discharge and h3 = 40 Btu/lb at the condenser outlet, a plant circulating 40 lb/min rejects how much heat at the condenser?

• A3,600 Btu/min (18.0 tons of rejection)
• B2,800 Btu/min (14.0 tons of rejection)
• C1,600 Btu/min (8.0 tons of rejection)
• D400 Btu/min (2.0 tons of rejection)

Field-erected copper refrigerant tubing for non-ammonia systems is specified as Type ACR and commonly manufactured to:

• AASTM B88 Type M only, marked for potable water
• BASTM B280 (and related ACR standards listed in IMC Table 1107.4)
• CASTM A53 Type F steel pipe
• DDWV copper marked for drainage

While brazing copper refrigerant joints, a small flow of dry nitrogen should be passed through the tubing to:

• AIncrease the brazing temperature
• BPrevent internal copper oxide scale that later circulates as contamination
• CReplace the need for a vacuum after assembly
• DFlux the joint from the inside

Suction lines are insulated primarily to:

• AKeep the compressor discharge hot enough for oil return
• BLimit heat gain into the cold vapor and prevent surface condensation
• CRaise evaporating pressure by adding heat
• DMeet electrical code clearance to luminaires

Per IMC 2021 Section 1109.2.7, refrigerant piping outside the equipment room shall be identified at intervals not exceeding:

• A5 feet, with 1/8-inch letters showing pipe diameter only
• B20 feet, with lettering at least 1/2 inch high showing refrigerant designation and safety…
• C50 feet, with color paint only and no text
• D100 feet, showing compressor brand only

IMC 2021 Section 1109.2.1 requires exposed refrigerant piping in open spaces that afford passage to be not less than:

• A5 feet 0 inches above the finished floor
• B6 feet 8 inches above the finished floor
• C7 feet 3 inches above the finished floor
• D10 feet 0 inches above the finished floor

IMC 2021 Section 1107.4.1 requires steel pipe for Group A2, A3, B2, and B3 refrigerants to be at least Schedule 80 when the size is:

• A4 inches and larger only
• B1-1/2 inches or less in diameter
• CAny size above 6 inches
• DCopper ACR tube 7/8 inch OD

IMC 2021 Section 1109.2.3 prohibits refrigerant piping in which location?

• AA machinery room complying with Section 1105
• BAn interior exit stairway
• CThe exterior of the building, vented to outdoors
• DA rooftop pipe rack serving air-cooled condensers

A double suction riser is used on a DX system so that:

• ALiquid refrigerant can freely drain into the compressor at all loads
• BHigh-load gas flows in both pipes with low pressure drop, while low-load gas still reache…
• CThe liquid line can be one size smaller
• DHot-gas defrost can be omitted

IMC 2021 Section 1107.1 states that piping material and installation for R-717 (ammonia) shall comply with:

• AIMC Table 1107.4 copper ACR rules only
• BIIAR 2
• CASTM B280 exclusively
• DThe International Plumbing Code water-pipe chapter

A liquid line rises 24 feet. Liquid density is 72 lb/ft³. The static pressure drop due to lift is closest to:

• A3 psi
• B8 psi
• C12 psi
• D24 psi

Suction vapor flows at 12 lb/min with a density of 0.40 lb/ft³ in a pipe whose internal area is 4.0 in². Gas velocity is closest to:

• A540 fpm
• B2,160 fpm
• C4,320 fpm
• D1,080 fpm

A discharge line has 40 feet of pipe, four long-radius elbows at 4 equivalent feet each, and one angle valve at 16 equivalent feet. If the friction chart shows 3.0 psi per 100 equivalent feet, total friction drop is:

• A1.2 psi
• B2.2 psi
• C3.0 psi
• D7.2 psi

The condenser in a vapor-compression system:

• AAbsorbs heat from the refrigerated space at low pressure
• BRejects the evaporator load plus compressor heat of compression to air or water
• CMeters liquid into the evaporator
• DStores only oil for the compressor

A liquid receiver is installed to:

• AStore spare high-pressure liquid so charge can vary with load and so the system can be pu…
• BSeparate oil from suction gas
• CReplace the condenser
• DRaise suction pressure at light load

A suction-line accumulator is intended to:

• AStore high-pressure liquid for pump-down
• BTrap liquid slugs and meter oil-laden liquid back to the compressor in small amounts
• CRaise condensing pressure in cold weather
• DReplace the TXV

An oil separator is normally installed in the:

• ALiquid line after the receiver
• BCompressor discharge line before the condenser
• CCondensate drain from the evaporator pan
• DCooling-tower makeup line

A thermostatic expansion valve (TXV) modulates flow by responding primarily to:

• ACompressor amperage
• BEvaporator-outlet superheat
• CCooling-tower basin level
• DDischarge-line oil temperature only