RETA CIRO flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Saturation temperature
- The temperature at which a refrigerant boils or condenses at a given pressure, with liquid and vapor present together. Raising the pressure raises the saturation temperature.
- Superheat
- The difference between the actual temperature of vapor and the saturation temperature at the same pressure. Measured at the evaporator outlet, it confirms the coil is fully fed with liquid.
- Subcooling
- The difference between saturation temperature and the actual liquid temperature at the same pressure. It proves the liquid line is solid and increases the refrigerating effect per kilogram.
- Compression ratio
- Absolute discharge pressure divided by absolute suction pressure. A high ratio raises discharge temperature, reduces volumetric efficiency, and pushes the system toward two-stage compression.
- One ton of refrigeration
- A capacity of 12,000 Btu per hour, 200 Btu per minute, or 3.517 kilowatts of heat removal. It is the standard basis for rating refrigeration equipment.
- Latent heat of vaporization
- The heat absorbed when a liquid changes to vapor at constant saturation temperature. Ammonia's high latent heat means a smaller mass flow is needed for a given capacity.
- Coefficient of performance
- Refrigerating effect divided by work of compression in the same units. A higher value means more cooling is produced per unit of energy input to the compressor.
- Low side
- The portion of the system at evaporating pressure: evaporator, suction line, accumulator, and low-pressure receiver, extending up to the compressor suction connection.
- Flooded evaporator
- An evaporator kept completely full of liquid refrigerant, with vapor separated in a low-pressure receiver and liquid recirculated by gravity or by a pump.
- Overfeed rate
- The mass of liquid refrigerant supplied to an evaporator divided by the mass evaporated there. Pumped recirculation systems commonly run between two and four to one.
- Evaporative condenser
- A condenser in which water sprayed over the coil evaporates into an air stream, rejecting heat. It needs water treatment and bleed to control scale and biological growth.
- Thermosyphon oil cooling
- Liquid refrigerant from the receiver circulates to the oil cooler because of density difference and returns as vapor to the condenser, cooling compressor oil without a pump.
- Hot gas defrost
- Discharge vapor from the compressor is routed through an evaporator to melt frost from the coil. A drain-down period follows before the coil returns to refrigeration.
- EPR valve
- Evaporator pressure regulator. It maintains a minimum evaporating pressure in a coil, keeping the coil temperature from dropping too low for the product or the room.
- Ammonia IDLH
- The immediately dangerous to life or health concentration for ammonia is 300 parts per million. Entry at or above this level requires supplied-air respiratory protection.
- Ammonia PEL
- The OSHA permissible exposure limit for ammonia is 50 parts per million as an eight-hour time-weighted average. Gas detectors are usually set to alarm well below that.
- Ammonia flammability range
- Ammonia will burn in air at roughly 15 to 28 percent by volume. A high-energy ignition source is needed, and the odor is detectable long before that range.
- PSM threshold, ammonia
- OSHA Process Safety Management applies to ammonia systems containing 10,000 pounds or more, requiring process hazard analysis, written operating procedures, training, and mechanical integrity programs.
- Pump-down procedure
- Refrigerant is removed from the section to be serviced and stored in a receiver or another part of the system, then the isolated section is bled to zero pressure and verified.
- Lockout/tagout
- Isolating every energy source, applying locks and tags, and trying the equipment to confirm it will not start before maintenance begins on the machine.
- Ohm's law
- Voltage equals current multiplied by resistance, written V = I × R. It applies to DC circuits and to AC circuits that are purely resistive.
- Electrical power formula
- Power in watts equals voltage times current, P = V × I. It can also be written as I²R or V²/R for resistive loads.
- Series circuit
- A circuit with only one current path. Current is the same through every component, total resistance is the sum, and the source voltage divides across the loads.
- Parallel circuit
- A circuit with more than one current path. Voltage is the same across every branch, current divides, and total resistance is lower than the smallest branch resistance.
- Three-phase power
- For a balanced three-phase load, power equals the square root of three times line voltage times line current times power factor.
- Motor synchronous speed
- Calculated as 120 times frequency divided by the number of poles. At 60 hertz a four-pole motor has a synchronous speed of 1800 rpm and runs slightly slower when loaded.
- Ladder diagram
- A control schematic drawn with two vertical power rails. Each rung is read left to right, and a coil energizes only when a complete path exists through the rung.
- Normally open contact
- A contact drawn open when its operating device is de-energized. It closes to complete the circuit when the coil, switch, or operator is actuated.
- Seal-in circuit
- A holding contact wired in parallel with a momentary start pushbutton. After the button is released, the contact keeps the coil energized until a stop device opens.
- Stop button wiring
- Stop pushbuttons and safety switches are wired in series with the coil, so opening any one of them breaks the path and de-energizes the circuit.
- Interlock
- A contact taken from one device and wired into another device's circuit so the two cannot run together or operate out of the required sequence.
- Overload heater
- A thermal element in a motor starter that bends or melts when sustained current exceeds the motor rating, opening the control circuit through the overload contact.