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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Household electrical appliances. Electric kettles, water heaters. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Household Appliances Electric kettle invented in 1900 by the American engineer Whitcomb. A modern electric kettle (no longer metal, but plastic) has the shape of a cylinder, of smaller diameter and greater height, does not take up much space on the table, boils faster, because the heat from the heating element rises vertically and heats all layers of water. Heat loss during this heating is minimal. A kettle of this shape retains heat longer. The heat-resistant, heat-saving, durable case also contributes to the preservation of heat. In a modern kettle, water is heated by an electric heater. To protect against moisture, it is placed inside a metal tube that serves as a screen. Specialists of the Moscow Institute of Biomedical Problems found that among kitchen electrical appliances, new electric kettles have the smallest, negligible electromagnetic field strength, which comes more from local electrical wiring. The modern plastic case of the kettle protects (isolates) from dangerous voltage in the event of a malfunction. About the design of the electric kettle. The case is placed on a stand, easy to install on it and just as easy to remove. The stand is equipped with a contact connector; one half of the connector is connected to the power cord, the other half is located in the bottom of the case, where it is connected to the heating element through switches. When the kettle is lifted, the connector breaks and the contacts of the stand are closed with protective shutters, which prevents accidental contact with current-carrying conductors and moisture on them. There is also a kettle with a semi-automatic opening of the connector - the separation of one part of the connector from the other occurs when you press a key located on the handle. Dividing the kettle into two parts - body and stand - allows you to use it as freely as a kettle heated on fire - fill it with water and carry it around the room, pour boiling water. At the same time, there is no need to take care of the power cord, which in the old model had to be held in the hand, which created inconvenience. The kettle has two switches. One of them - semi-automatic - for manual switching on of the heating element and automatic switching off when water boils. The other is to automatically turn off the heating element when overheating, when there is little or no water in the kettle. In both cases, bimetallic single-layer or multi-layer plates are used as sensors. In a semi-automatic switch, a bimetallic plate and the switch itself, triggered by spring pressure on it, are combined and are called a controller. Automatic shutdown of the kettle with hot water has advantages: it is the ultimate energy savings and, very importantly, water does not boil over. According to experts, it is desirable to boil water once, especially tap water. When boiling, demineralized steam comes out and the concentration of salts in the remaining water increases. The market offers a variety of electric kettles. They are made using the same technology, are reliable, have a modern design, about a dozen colors, a plastic case made of especially heat-resistant plastic, a top cover with a blocking lock that protects against accidental splashing of hot water, a handle that does not heat up from hot water, a water level indicator with symbols min and max (minimum and maximum), connection to the mains through a stand, automatic shutdown when water boils and protection against overheating in the absence of water. Unlike sophisticated household appliances, electric kettles are immune to power surges within 150-240 V. Power consumption, depending on the model, is 1800-2200 W, the speed of obtaining 250 g of boiled water at a voltage of 220 V and a power of 2000 W is 1 min. ., 750 g - 3, 1 l - 4 min. There are many types of electric kettles. An interesting electric kettle with a double-sided water indicator and a cord that can be retracted inside the stand. There is a kettle with a heating element located in the bottom of the body in a horizontal plane, which makes it possible to boil water 25% faster (1 liter of water boils in 3 minutes) and pour a minimum of water (1-2 cups). At least 500-700 g of water should be poured into kettles with an open heating element. Another important difference of such an electric kettle is the placement of an electrical connector in the center of the stand, which allows rotating its body by 360 °. Steam in this kettle is supplied from the top of the body through a tube down to a temperature sensor that turns off the electricity when the water temperature reaches 100 ° C. Another feature of this model is that the controller is located in the same node with both bimetallic plates. There is an electric kettle with two removable nylon filters - in the lid and in the spout, which allows you to pour cold water without lifting the lid, facilitates the removal of scale, since the internal surfaces of the body are polished, without roughness. New models are constantly appearing on the market - with adjustable water heating temperature, full protection against scale of internal surfaces, a transparent case cover, completely made of heat-resistant transparent glass, as well as metal in the form of "retro" with a classic arc handle, with a sound signal to start boiling water. The taste of tea largely depends on the quality of the water used, so for making tea it is recommended to use jug cleaners that remove unwanted impurities, preserve the mineral composition of the water and do not require connection to water supply and electricity. New electric kettles are safe to use, but children should not be allowed to touch the stand when the kettle body is raised and the mains plug is connected to the socket. It is necessary to avoid getting water on the stand, you can wipe it when disconnecting the plug from the mains. At the end of tea drinking, in order to increase the service life of the heating element, it is advisable to pour out the remaining water from the kettle and dry the kettle with the lid open. To prolong the service life of the controller and connector contacts, do not remove the switched on electric kettle from the stand prematurely. If you do not intend to heat the water to the boiling temperature before removing the kettle, you must turn off the controller. To restart the kettle after its automatic shutdown at a water temperature of 100 °C, it is advisable to maintain an interval of 1-2 minutes. In electric kettles with a filter, it is not recommended to pour cold water through the spout, as sediment will appear on the outside of the filter, which will then fall into the cup. You can rinse electric kettles from scale with vinegar: pour three cups of 3% vinegar and add water to the "max" mark. The kettle is left with this composition overnight (in no case do they boil), and in the morning it is poured out, the sediment on the filter is removed with a soft cloth. The kettle is filled with water, boiled twice, and the inner surface is wiped with a clean, damp cloth. The commercially available drug "Antinakipin" removes scale more effectively. The developers of electric kettles provided for the possibility of their disassembly and replacement of failed parts. Most often, heating elements fail - they "perforate" due to exposure to salts and constant exposure to water. The gold-plated heating element slows down this process, but does not permanently eliminate it. Breakers also burn out, most often due to rapid reclosing after an automatic shutdown. The principle of the device and operation of devices united by the general purpose of heating water is the same. The difference lies only in their design features. The basis of these devices is a tubular electric heater - a heating element (Fig. 92), which is a thin-walled metal tube made of carbon steel grade 10 or 20 with a wire spiral with a very high electrical resistivity enclosed in it.
The ends of the spiral are connected to the rods that come out of the hermetically sealed tube and serve as contacts for connecting the heating element to the network. In order to avoid closing the spiral on the body of the tube, the latter is filled with a loose insulator that conducts heat well and does not conduct electricity at all (quartz sand or crystalline magnesium oxide - the so-called periclase). The insulator filling the tube under high pressure turns into a monolith, so it not only performs an insulating function, but also securely fixes the spiral along the axis of the tube. The heating element is a fairly versatile device designed for use in various water heating devices. Therefore, depending on the purpose, heating elements are made of various materials (including refractory ones) and various shapes (after crimping, the tube can be bent in any way). The temperature of the working surface of heating elements has a fairly wide range: from 450 ° C (for household electric heaters) to 800 ° C (for heating fats, oils, low-melting metals in industrial installations). The average service life of heating elements with proper operation is up to 10 hours of continuous operation. Since, as already mentioned, there are a large number of types of heating elements, when buying them, special attention should be paid to the marking, which indicates not only the metric parameters of its elements, but also the rated power in kW and voltage in V, the tube material, the environment for which The heating element is intended, as well as the type of climatic modification in accordance with GOST. Among the shortcomings of heating elements, one should note their high metal consumption, the use of expensive materials (nichrome, stainless steel) in them and, as a result, their high cost. In addition, heating elements are not subject to repair. The simplest household water heater that uses a heating element is an electric boiler; in fact, a boiler is a heating element with a handle and a cord. The handle of the boiler has a hook (or is itself made in the form of a hook), due to which the boiler is fixed on the edge of the container in which the water is heated. All kinds of electric kettles, samovars, coffee pots are containers for heating water, in the lower part of which a heating element of one form or another is mounted. When installing a hot shower in a summer cottage, low-pressure storage water heaters (EVAN type) are often used with the same tubular heating element with a power of up to 1,24 kW. The diagram of its connection to the water pipe and shower sprinkler is shown in fig. 93.
EVAN heaters are produced with a capacity of 10, 40 and 100 liters. Warming up the water to the temperature at which the thermostat knob is set occurs, respectively, in 1, 2, 3, and 7, 8 hours. The serviceability and duration of the service life of electric water heaters depends on how correctly they are operated and looked after. The rules for operating such devices are simple, so remembering and adhering to them will not be difficult. It should be remembered that devices intended for heating water (electric kettles, coffee pots, etc.) can only be connected to the mains if they are filled with water by at least 1/3 of their volume, otherwise the heating element will burn out (and repair , as you know, it is not subject). There are special marks on the heating tube of the boiler, indicating the lower and upper limits of filling the tank with water before turning on the boiler in the mains. If the water does not reach the lower risk, then you can burn the device; if the water rises above the upper risks, then there is a possibility of a short circuit. A sharp temperature drop adversely affects the coil of the heating element, so you can not pour water from the kettle, samovar, etc. until the heating element is exposed, until it has cooled down. Also, do not pour or top up cold water on the heated surface of the tubular heater. Long-term operation of water heaters (especially with hard water) leads to the formation of scale (precipitation of mineral salts) on the surface of the heating element, which reduces thermal conductivity and leads to wasteful energy consumption. Therefore, scale should be removed periodically using one of the proposed recipes.: - carefully pour 1 volume parts of water into 4 volume part of hydrochloric acid; rinse the inner surface of the device container and the surface of the heating element with the resulting solution, after which the device is thoroughly rinsed with clean water; - if the kettle is plastic, then instead of rather aggressive hydrochloric acid, it is better to use soft citric acid. To do this, boil 0,5 liters of water in a kettle and add 25 g of citric acid powder. Leave to soak for 15 minutes, then rinse the kettle thoroughly with clean water; - you can pour 0,5 l into the kettle (or until the heating element is completely covered) 8% white vinegar, leave for 1 hour without boiling, then drain the liquid, and rinse the kettle with clean water; - you can also use a folk remedy - put clean potato peels into a container and pour water, boil, remove the peels and rinse the container with a heating element with plenty of clean water. And now about the malfunctions of electric water heaters. If the device is connected to the mains, its cord, plug and socket are working, but the water does not heat up, you need to check the heating element (heater), or rather, the serviceability of its contact connections. To do this, disconnect the device from the network, remove all water from the container, and dry it. Then you should unscrew the screws securing the tray and remove it (so the heating element will be more accessible). Very often, the cause of the malfunction is hidden in a broken contact at the connection points of the heating element leads; therefore, it is they who are checked first of all: the fixing screws are unscrewed and the clamping washer is removed. If the connections are really broken, then they are restored. If everything is in order with the contacts, then the heating element itself may be faulty, it should be replaced: the contacts of the heating element leads are opened, the heating element is replaced with a new one. Author: Korshevr N.G.
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