RETA CARO flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Ton of refrigeration
- A cooling rate equal to 12,000 Btu per hour, or 200 Btu per minute, equivalent to about 3.517 kilowatts of refrigeration capacity.
- Sensible heat
- Heat that changes the temperature of a substance without changing its phase, calculated as mass times specific heat times temperature difference.
- Latent heat
- Heat absorbed or released during a phase change at constant temperature, such as boiling liquid refrigerant in an evaporator or condensing vapor in a condenser.
- Superheat
- The number of degrees the refrigerant vapor at a given point is above its saturation temperature for the existing pressure, commonly measured at evaporator outlet.
- Subcooling
- The number of degrees the liquid refrigerant is below its saturation temperature at the existing pressure, typically measured at the condenser outlet or liquid line.
- Pressure ratio
- Absolute discharge pressure divided by absolute suction pressure; higher ratios increase discharge temperature and reduce compressor volumetric efficiency.
- Thermostatic expansion valve
- A metering device that regulates refrigerant flow into the evaporator to maintain a set superheat, using a bulb sensing suction line temperature.
- Volumetric efficiency
- The ratio of actual vapor volume pumped to the compressor displacement volume, reduced by clearance volume, re-expansion, and pressure ratio.
- Evaporator approach
- The temperature difference between the medium being cooled and the refrigerant saturation temperature in the evaporator; a larger approach indicates reduced heat transfer.
- Condenser subcooling purpose
- Subcooling the liquid before the expansion valve ensures a solid liquid column at the valve and prevents flash gas from reducing valve capacity.
- Compressor displacement
- The theoretical volume swept by the compressor pistons per unit time, calculated from bore area, stroke, speed, and number of cylinders.
- Liquid line sizing
- Liquid lines are sized small enough to limit refrigerant charge but large enough to keep pressure drop low and prevent flashing before the expansion valve.
- Suction line sizing
- Suction lines are sized to minimize pressure drop, since excess drop lowers suction pressure and reduces compressor capacity and efficiency.
- Refrigeration cycle order
- The sequence is compressor, condenser, expansion device, evaporator; the compressor raises pressure, the condenser rejects heat, and the evaporator absorbs heat.
- Flash gas
- Vapor formed when liquid refrigerant pressure drops below its saturation pressure; excessive flash gas at the expansion valve reduces cooling capacity.
- Ammonia IDLH
- The immediately dangerous to life or health concentration for ammonia is 300 ppm, the level at which escape without respiratory protection may fail.
- Ammonia vapor density
- Ammonia vapor is about 0.6 times the density of air, so it is lighter than air and tends to rise and collect at ceilings and high points.
- Ammonia OSHA PEL
- The permissible exposure limit for ammonia is 50 ppm as an eight-hour time-weighted average; the ACGIH short-term exposure limit is 35 ppm.
- Ammonia flammability range
- Ammonia vapor is flammable in air at roughly 15 to 28 percent by volume and requires a strong ignition source because it ignites with difficulty.
- Water on ammonia vapor
- Water spray absorbs ammonia vapor effectively because ammonia is highly soluble in water, but water must not be sprayed into liquid ammonia pools.
- Ammonia PPE
- Response PPE includes SCBA or full-face respirator, chemical splash goggles, and ammonia-resistant gloves such as butyl or neoprene rather than natural rubber.
- Ammonia eye first aid
- Flush exposed eyes with copious water for at least 15 minutes, remove contaminated clothing, and obtain medical evaluation promptly after exposure.
- Machinery room ventilation
- Ammonia machinery rooms require mechanical ventilation, ammonia detection with alarm and shutdown interlocks, and outward-opening emergency exits separated from occupied areas.
- King valve
- A manual shutoff valve at the liquid receiver outlet used to isolate the liquid supply during emergencies or pump-down procedures.
- Pump-down procedure
- A controlled sequence that draws refrigerant vapor from a section into the receiver or condenser to reduce the charge before repair or isolation.
- Ammonia detection alarm
- Fixed ammonia sensors in machinery rooms trigger alarms and often ventilation or shutdown interlocks at set low and high concentration thresholds.
- Ammonia health effects
- Ammonia is corrosive to eyes, skin, and respiratory tissue; inhalation causes burning, coughing, and pulmonary injury, and liquid contact can cause frostbite.
- SCBA entry rule
- Never enter an ammonia release area without self-contained breathing apparatus and a standby person outside who can assist or summon help.
- Ammonia transport classification
- Anhydrous ammonia is classified as a toxic gas (Division 2.2 with toxic subsidiary risk) for transport, requiring placarding and emergency response information.
- Ammonia oil fire hazard
- Oil-soaked insulation or debris near an ammonia leak can ignite and sustain fire, so contaminated materials should be removed and ignition sources controlled.
- Ammonia emergency shutdown
- Close isolation and king valves to stop flow, isolate the affected section, and avoid operating equipment that could spread vapor or create ignition sources.
- Ammonia odor threshold
- Ammonia has a pungent odor detectable at roughly 5 to 50 ppm, well below the IDLH, but odor fatigue can reduce warning effectiveness.