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domestic refrigerator[də′mes·tik ri′frij·ə‚rād·ər]
(also household refrigerator), an appliance that is used for the short-term preservation of food products in the home by means of refrigeration. Depending on the type of refrigerating machine used, domestic refrigerators are classified as compression-type, absorption-type, and thermoelectric.
The first domestic refrigerators, which used vapor-compression machines, appeared in 1910 in the USA. Absorption-type domestic refrigerators were first produced in 1925 in Sweden. The first thermoelectric domestic refrigerators were manufactured in the second half of the 1950’s. In the USSR, the first compression-type domestic refrigerators (the KhTZ-120) were produced in 1939, the first absorption-type domestic refrigerators (the Gazoapparat) were manufactured in 1945, and the first prototypes of a thermoelectric refrigerator, which uses thermoelectric cooling, were produced in 1951. The mass production of Soviet compression-type domestic refrigerators (the ZIL) began in 1951.
A domestic refrigerator is a metal cabinet with a built-in hermetically sealed refrigerating unit (Figure 1). Inside the cabinet is a cold chamber with shelves for storing products. Heat insulation is placed between the walls of the cold chamber and the case of the refrigerator. The air in the cold chamber is cooled by means of heat transfer between the air and the cold surface of the evaporator. The necessary temperature conditions in the refrigerator are provided by the brief periodic—that is, cyclic—operation of the refrigerating unit, which is switched on by means of a thermal relay. Domestic refrigerators have a storage space of 20 to 800 liters.
Depending on their purpose, Soviet domestic refrigerators are divided into the following four categories: those intended for the storage of unfrozen products (such refrigerators lack a freezer compartment), those intended for the short-term storage (for several days) of frozen products, those intended for the mediumterm storage (up to several weeks) of frozen products, and those intended for the long-term storage (up to three months) of frozen products. The assignment of a refrigerator to one of these categories depends on whether the refrigerator has a freezer compartment and on the air temperature in the freezer compartment. For the information of consumers, refrigerators intended for short-term storage bear one star, those intended for medium-term storage bear two stars, and those intended for long-term storage bear three stars. The temperature in the freezer compartment is –6°C in one-star models, –12°C in two-star models, and not higher than –18°C in three-star models.
The one-, two-, and three-star models are two-temperature refrigerators; the two- and three-star models have one, two, or more compartments. In two-compartment models, a thick insulated partition separates the freezer compartment and the main compartment, where the temperature is above freezing. Each of the two compartments has its own door. Multiple-compartment refrigerators have at least three compartments, each with its own door, for the storage of various products. According to the extent to which their operation is automated, refrigerators are classified as having manual, semiautomatic, or automatic defrosting. Depending on the method used for circulating the air in a refrigerator, a distinction is made between refrigerators with natural circulation and those with forced circulation, which is maintained by a fan.
In three-star refrigerators with natural convection, each compartment, as a rule, is cooled by a separate evaporator. In refrigerators with forced circulation, a fan draws air through a single evaporator, which is a pipe coil with plate fins. The evaporator and fan are usually installed behind the rear wall of the freezer compartment. Most of the cold air (75–85 percent) is supplied to the freezer compartment; the rest of the cold air is delivered to the main compartment, where the temperature is above freezing. In such refrigerators, absolutely no frost is deposited on the products or the walls. The moisture contained in the air accumulates as frost on the evaporator, which is located behind the wall of the freezer compartment, so that only dry air enters the compartment. Since the evaporator is not in contact with the products, the heating of the evaporator during defrosting does not affect the temperature of frozen products. Therefore, automatic defrosting may be carried out several times a day.
Domestic refrigerators may be stationary or portable. Stationary refrigerators are classified as free-standing, wall-type, and built-in (that is, built into a kitchen or reception-room furniture unit). Portable models are mainly absorption-type and thermoelectric refrigerators. In addition, absorption-type refrigerators are classified, depending on the heat source, as electric, gas-fired, kerosene-burning, and combination-type. Electric refrigerators are the most widely used. The limited use of gas-fired refrigerators is due mainly to safety considerations and also to difficulties associated with the connection of such refrigerators to a gas distribution system. Kerosene-burning refrigerators are used mainly aboard ships and as portable appliances.
Most of the domestic refrigerators manufactured today are of the compression type. Absorption-type refrigerators account for 5–10 percent of the total production. In comparison with compression-type refrigerators, absorption-type refrigerators are bulkier and heavier, consume more electrical energy (more by a factor of 1.5–2), and have a smaller freezer compartment. Thermoelectric refrigerators are not widely used, since they are expensive and have higher power requirements than compression-type refrigerators. Most thermoelectric refrigerators have a small storage space (up to 60 liters).
Domestic refrigerators are produced in more than 60 countries. More than 25 million such refrigerators are manufactured each year. The USSR (with 5.6 million domestic refrigerators produced in 1975), the USA, and Italy manufacture the largest number of domestic refrigerators each year.
L. N. VAIN