Questions and Answers
What is an air cooling evaporator?
For what reason does heat transfer somewhat slowly between air and the refrigerant in an air cooling evaporator?
Air has relatively low density.
Air defrosting is most commonly used on evaporator in _____ applications.
medium-temperature
A plain coil submerged and mounted inside a container filled with a liquid that provides good heat transfer is a(n) _____ evaporator.
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Why might a designer of a liquid-cooling evaporator use a brine bath rather than a sweet water bath?
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Fin-and-tube evaporators circulating the most common types of refrigerants generally have fins made of _____
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In general, the more fins an air-cooling evaporator has, _____
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Dead air and hot spots in a conditioned space can often be eliminated by using _____
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The air cooling evaporators that are most effective at heat transfer are _____ evaporators.
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Defrost timers commonly control the operation of the following, except for ____.
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Defrost timers end a defrost cycle using the following variables, except for _____.
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The condition in which a defrost cycle continues too long and conditioned space temperature is raised too high is called _____
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When melted frost cannot be directly drained by gravity alone, it must be removed using a(n) _____
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The method of defrost that involves circulating a hot liquid in and around the evaporator is _____ defrosting.
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The method of defrost that involves circulating air from the conditioned space over an evaporator after the compressor cycles off is _____ defrosting.
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The method of defrost that involves energizing electric heating elements is _____ defrosting.
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The method of defrost that involves removing refrigerant from the evaporator is _____ defrosting.
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The method of defrost that involves manually or automatically running tap water over an evaporator is _____ defrosting.
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The method of defrost that involves circulating high-pressure refrigerant through an evaporator is _____ defrosting.
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What does a liquid line solenoid valve (open) corresponds to?
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What does a defrost solenoid valve (closed) correspond to?
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What does a condenser check valve correspond to?
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What does a defrost thermostat correspond to?
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What does a crankcase pressure regulator correspond to?
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What does a pressure-regulating valve correspond to?
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What does a condenser correspond to?
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What does a three-way solenoid valve correspond to?
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What does a bypass check valve correspond to?
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What does a liquid receiver correspond to?
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Study Notes
Air Cooling Evaporators
- An air cooling evaporator facilitates heat transfer, but slow transfer occurs due to the low density of air.
- Effective air cooling evaporators include microchannel designs.
Defrosting Methods
- Air defrosting is commonly used in medium-temperature applications to remove frost.
- Methods of defrosting include:
- Nonfreezing solution defrosting: Circulates hot liquids around the evaporator.
- Electric defrosting: Uses air from the conditioned space after compressor cycles off.
- Off-cycle defrosting: Energizes electric heating elements.
- Pump-down defrosting: Involves removing refrigerant from the evaporator.
- Water defrosting: Manually or automatically uses tap water on the evaporator.
- Hot gas defrosting: Circulates high-pressure refrigerant through the evaporator.
Evaporator Types and Components
- An immersed evaporator is a plain coil submerged in a liquid that enhances heat transfer.
- Liquid-cooling evaporators may utilize a brine bath to cool below 32°F (0°C) without freezing.
- Fin-and-tube evaporators commonly have aluminum fins to optimize heat exchange.
Controls and Valves
- Defrost timers regulate defrost cycles but do not control expansion valves.
- Over defrosting occurs when the cycle lasts too long, increasing the conditioned space temperature.
- Condensate pumps are necessary when melted frost must be removed beyond gravity’s assistance.
Cooling System Components
- Various valves and components are essential in cooling systems, including:
- Liquid line solenoid valve: Controls refrigerant flow.
- Defrost solenoid valve: Manages defrost cycles.
- Condenser check valve: Ensures proper refrigerant flow direction.
- Defrost thermostat: Senses and manages defrosting.
- Crankcase pressure regulator and Pressure-regulating valve: Maintains optimal pressures within the system.
- Understanding the function of these components ensures effective management of heat exchangers.
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Description
Test your knowledge on heat exchangers with these flashcards from Chapter 21. Explore definitions and applications related to air cooling evaporators and their operational principles. Enhance your understanding of how heat transfer occurs in various refrigeration scenarios.
