Auto-defrost – Wikipedia

Frost suppression in refrigerators or freezers
Auto-defrost, automatic defrost or self-defrosting is a technique which regularly defrosts the evaporator in a refrigerator or deep-freeze. Appliances using this proficiency are much called frost free, frostless, or no-frost .

mechanism [edit ]

A defrost timer taken out of a family refrigerator The defrost mechanism in a refrigerator heats the cool element ( evaporator gyrate ) for a curtly menstruation of time and melts the frost that has formed on it. The result body of water drains through a duct at the back of the unit. Defrosting is controlled by an electric or electronic timer : For every 6, 8, 10, 12 or 24 hours of compressor operation it turns on a defrost fastball for 15 minutes to half an hour.

The defrost fastball, having a typical power rat of 350 W to 600 W, is mounted precisely below the evaporator in top- and bottom-freezer models and below and sometimes besides in the center of the evaporator in side-by-side models. It may be protected from shortstop circuits by means of fusible links. In older refrigerators the timekeeper ran endlessly. In newer designs the timer only runs while the compressor runs, so the more the refrigerator door is closed, the less the heater will be on and the more energy will be saved. A defrost thermostat opens the fastball racing circuit when the evaporator temperature rises above a preset temperature, 40°F ( 5°C ) or more, thereby preventing excessive heat of the deep-freeze compartment. The defrost timer is such that either the compressor or the defrost heater is on, but not both at the same time. Inside the deep-freeze, air is circulated by means of one or more fans. In a typical design cold air from the deep-freeze compartment is ducted to the fresh food compartment and circulated back into the deep-freeze compartment. Air circulation helps sublimate any ice or frost that may form on freeze items in the deep-freeze compartment. While defrosting, this fan is stopped to prevent heated-up air from reaching the food compartment. alternatively of the traditional cooling system elements being embedded in the deep-freeze liner, auto-defrost elements are behind or beneath the lining. This allows them to be heated for short periods of time to dispose of frost, without heating the contents of the deep-freeze. alternatively, some systems use the hot gas in the condenser to defrost the evaporator. This is done by means of a circuit that is cross-link by a tripartite valve. The hot gasoline cursorily heats up the evaporator and defrosts it. This system is primarily used in commercial applications such as ice-cream displays.

application [edit ]

While this technique was in the first place applied to the refrigerator compartment, it was later used for deep-freeze compartment deoxyadenosine monophosphate well. A combined refrigerator/freezer which applies self-defrosting to the refrigerator compartment only is normally called “ partial frost free ” or semi-automatic defrost ( some brands call these “ car Defrost ” while Frigidaire referred to their semi-automatic models as “ Cycla-Matic, ” Kelvinator much named these models as “ Cyclic Defrost ” ). These refrigerators normally have a pan underneath where water from the melted frost in the refrigerator segment evaporates. Freezers with automatic defrost and combined refrigerator/freezer units which besides apply self defrosting to their deep-freeze compartment are called “ frost barren ”. The latter normally feature an air connection between the two compartments with the air passing to the refrigerator compartment regulated by a damper. By this means, a control share of the air coming from the deep-freeze reaches the refrigerator. Some older models have no air circulation between their deep-freeze and refrigerator sections. alternatively, they use an freelancer cooling system ( for example : an evaporator coil with a defrost heater and a circulate fan in the deep-freeze and a cold-plate or open-coil evaporator in the refrigerator. “ Frost-Free ” refrigerator/freezer units normally use a heat component to defrost their evaporators, a pan to collect and evaporate water from the frost that melts from the cold denture and/or evaporator coil, a timer which turns off the compressor and turns on the defrost component normally from once to 4 times a day for periods normally ranging from 15 to 30 minutes, a defrost limiter thermostat that turns off the heat chemical element before the temperature rises excessively much while the timekeeper is hush in its defrost phase. Some models besides feature a drain fastball to prevent ice from blocking the drain.

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other early types of refrigerators besides use hot gas defrost alternatively of electric heaters. These reverse the evaporator and condenser sides for the defrost cycle. Some newer refrigerator/freezer models have a calculator that monitors how many times each door is opened and uses this data to control defrost scheduling thereby reducing world power use .

Advantages [edit ]

  • No need to manually defrost the frost buildup, therefore power consumption will not increase with time.
  • Food packaging is easier to see.
  • Most frozen food will not stick together.
  • Smells are limited, especially in total frost-free appliances because the air always circulates.
  • Better temperature management.

Disadvantages [edit ]

  • The system can be more expensive to run when usage is high and if the fan continues or starts to run when the door is opened.[1]
  • A thermal cutout safety device is required to prevent overheating of the heating element.
  • Increased electrical and mechanical complexity compared to a basic upright freezer or chest freezer, making it more prone to component failure.
  • The temperature of the freezer contents rises during the defrosting cycles, especially if there is a light load in the freezer. This can cause “freezer burn” on articles placed in the freezer, from partially defrosting, then re-freezing
  • On hot, humid days condensation will sometimes form around the refrigerator doors.
  • Defrosting may not be completed by the time the defrost timer cycles back to normal operation (especially in hot, humid conditions with frequent door openings), leaving ice/frost on the evaporator coils. This condition can lead to “icing” which will interfere with the operation of the refrigerator.

In laboratories, self-defrosting freezers must not be used to store certain finespun reagents such as enzymes, because the temperature cycling can degrade them. In accession, water can evaporate out of containers that do not have a identical nasty cachet, altering the concentration of the reagents. Self-defrosting freezers should never be used to store flammable chemicals .

References [edit ]

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