- info@parsalandco.com
- +989124000464
- +989127093613
Menu
A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce thermal energy in a process known as dielectric heating. Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer 25–38 mm (1–1.5 inches) of a homogeneous, high water content food item.
The exploitation of high-frequency radio waves for heating substances was made possible by the development of vacuum tube radio transmitters around 1920. By 1930 the application of short waves to heat human tissue had developed into the medical therapy of diathermy. At the 1933 Chicago World’s Fair, Westinghouse demonstrated the cooking of foods between two metal plates attached to a 10 kW, 60 MHz shortwave transmitter. The Westinghouse team, led by I. F. Mouromtseff, found that foods like steaks and potatoes could be cooked in minutes.
The 1937 United States patent application by Bell Laboratories states:
This invention relates to heating systems for dielectric materials and the object of the invention is to heat such materials uniformly and substantially simultaneously throughout their mass. … It has been proposed therefore to heat such materials simultaneously throughout their mass by means of the dielectric loss produced in them when they are subjected to a high voltage, high frequency field.
However, lower-frequency dielectric heating, as described in the aforementioned patent, is (like induction heating) an electromagnetic heating effect, the result of the so-called near-field effects that exist in an electromagnetic cavity that is small compared with the wavelength of the electromagnetic field. This patent proposed radio frequency heating, at 10 to 20 megahertz (wavelength 30 to 15 meters, respectively). Heating from microwaves that have a wavelength that is small relative to the cavity (as in a modern microwave oven) is due to “far-field” effects that are due to classical electromagnetic radiation that describes freely propagating light and microwaves suitably far from their source. Nevertheless, the primary heating effect of all types of electromagnetic fields at both radio and microwave frequencies occurs via the dielectric heating effect, as polarized molecules are affected by a rapidly alternating electric field.
The invention of the cavity magnetron made possible the production of electromagnetic waves of a small enough wavelength (microwaves). The magnetron was a crucial component in the development of short wavelength radar during World War II. In 1937–1940, a multi-cavity magnetron was built by British physicist Sir John Turton Randall, FRSE and coworkers, for the British and American military radar installations in World War II. A higher-powered microwave generator that worked at shorter wavelengths was needed, and in 1940, at the University of Birmingham in England, Randall and Harry Boot produced a working prototype. They invented a valve that could produce pulses of microwave radio energy at a wavelength of 10 cm, an unprecedented discovery.
Sir Henry Tizard traveled to the U.S. in late September 1940 to offer the magnetron in exchange for their financial and industrial help (see Tizard Mission). An early 6 kW version, built in England by the General Electric Company Research Laboratories, Wembley, London, was given to the U.S. government in September 1940. The magnetron was later described by American historian James Phinney Baxter III as “[t]he most valuable cargo ever brought to our shores”. Contracts were awarded to Raytheon and other companies for the mass production of the magnetron.
In 1945, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a chocolate bar he had in his pocket. The first food deliberately cooked with Spencer’s microwave oven was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.
To verify his finding, Spencer created a high density electromagnetic field by feeding microwave power from a magnetron into a metal box from which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly. On 8 October 1945, Raytheon filed a United States patent application for Spencer’s microwave cooking process, and an oven that heated food using microwave energy from a magnetron was soon placed in a Boston restaurant for testing.
Another early discovery of microwave oven technology was by British scientists who in the 1950s used it to reanimate cryogenically frozen hamsters.
In 1947, Raytheon built the “Radarange”, the first commercially available microwave oven. It was almost 1.8 metres (5 ft 11 in) tall, weighed 340 kilograms (750 lb) and cost about US$5,000 ($61,000 in 2021 dollars) each. It consumed 3 kilowatts, about three times as much as today’s microwave ovens, and was water-cooled. The name was the winning entry in an employee contest. An early Radarange was installed (and remains) in the galley of the nuclear-powered passenger/cargo ship NS Savannah. An early commercial model introduced in 1954 consumed 1.6 kilowatts and sold for US$2,000 to US$3,000 ($20,000 to $30,000 in 2021 dollars). Raytheon licensed its technology to the Tappan Stove company of Mansfield, Ohio in 1952. Under contract to Whirlpool, Westinghouse, and other major appliance manufacturers looking to add matching microwave ovens to their conventional oven line, Tappan produced several variations of their built-in model from roughly 1955 to 1960. Due to maintenance (some units were water cooled), in-built requirement, and cost (US$1,295 ($13,000 in 2021 dollars)), sales were limited.
Japan’s Sharp Corporation began manufacturing microwave ovens in 1961. Between 1964 and 1966, Sharp introduced the first microwave oven with a turntable, an alternative means to promote more even heating of food. In 1965, Raytheon, looking to expand their Radarange technology into the home market, acquired Amana to provide more manufacturing capability. In 1967, they introduced the first popular home model, the countertop Radarange, at a price of US$495 ($4,000 in 2021 dollars). Unlike the Sharp models, a motor driven mode stirrer in the top of the oven cavity rotated allowing the food to remain stationary.
In the 1960s,[specify] Litton bought Studebaker’s Franklin Manufacturing assets, which had been manufacturing magnetrons and building and selling microwave ovens similar to the Radarange. Litton developed a new configuration of the microwave oven: the short, wide shape that is now common. The magnetron feed was also unique. This resulted in an oven that could survive a no-load condition: an empty microwave oven where there is nothing to absorb the microwaves. The new oven was shown at a trade show in Chicago,[citation needed] and helped begin a rapid growth of the market for home microwave ovens. Sales volume of 40,000 units for the U.S. industry in 1970 grew to one million by 1975. Market penetration was even faster in Japan, due to a less expensive re-engineered magnetron. Several other companies joined in the market, and for a time most systems were built by defence contractors, who were most familiar with the magnetron. Litton was particularly well known in the restaurant business.
While uncommon today, combination microwave-ranges were offered by major appliance manufacturers through much of the 1970’s as a natural progression of the technology. Both Tappan and General Electric offered units that appeared to be conventional stove top/oven ranges, but included microwave capability in the conventional oven cavity. Such ranges were attractive to consumers since both microwave energy and conventional heating elements could be used simultaneously to speed cooking, and there was no loss of countertop space. The proposition was also attractive to manufacturers as the additional component cost could better be absorbed compared with countertop units where pricing was increasingly market-sensitive.
By 1972, Litton (Litton Atherton Division, Minneapolis) introduced two new microwave ovens, priced at $349 and $399, to tap into the market estimated at $750 million by 1976, according to Robert I Bruder, president of the division. While prices remained high, new features continued to be added to home models. Amana introduced automatic defrost in 1974 on their RR-4D model, and was the first to offer a microprocessor controlled digital control panel in 1975 with their RR-6 model.
1974 Radarange RR-4. By the late 1970s, technological advances led to rapidly falling prices. Often called “electronic ovens” in the 1960s, the name “microwave oven” later gained currency, and they are now informally called “microwaves”.
The late 1970s saw an explosion of low-cost countertop models from many major manufacturers.
Formerly found only in large industrial applications, microwave ovens increasingly became a standard fixture of residential kitchens in developed countries. By 1986, roughly 25% of households in the U.S. owned a microwave oven, up from only about 1% in 1971; the U.S. Bureau of Labor Statistics reported that over 90% of American households owned a microwave oven in 1997. In Australia, a 2008 market research study found that 95% of kitchens contained a microwave oven and that 83% of them were used daily. In Canada, fewer than 5% of households had a microwave oven in 1979, but more than 88% of households owned one by 1998. In France, 40% of households owned a microwave oven in 1994, but that number had increased to 65% by 2004.
Adoption has been slower in less-developed countries, as households with disposable income concentrate on more important household appliances like refrigerators and ovens. In India, for example, only about 5% of households owned a microwave oven in 2013, well behind refrigerators at 31% ownership. However, microwave ovens are gaining popularity. In Russia, for example, the number of households with a microwave oven grew from almost 24% in 2002 to almost 40% in 2008. Almost twice as many households in South Africa owned microwave ovens in 2008 (38.7%) as in 2002 (19.8%). Microwave oven ownership in Vietnam was at 16% of households in 2008—versus 30% ownership of refrigerators; this rate was up significantly from 6.7% microwave oven ownership in 2002, with 14% ownership for refrigerators that year.
Consumer household microwave ovens usually come with a cooking power of 600 watts and up (with 1000 or 1200 watts on some models). The size of household microwave ovens can vary, but usually have an internal volume of around 20 liters (1,200 cu in; 0.71 cu ft), and external dimensions of approximately 45–60 cm (1 ft 6 in – 2 ft 0 in) wide, 35–40 cm (1 ft 2 in – 1 ft 4 in) deep and 25–35 cm (9.8 in – 1 ft 1.8 in) tall.
Microwaves can be turntable or flatbed. Turntable ovens include a glass plate or tray. Flatbed ones do not include a plate, so they have a flat and wider cavity .
By position and type, US DOE classifies them in (1) countertop or (2) over the range and built-in (wall oven for a cabinet or a drawer model).
Traditional microwaves rely on internal high voltage power from a line/mains transformer, but many newer models are powered by an inverter. Inverter microwaves can be useful for achieving more even cooking results, as they offer a seamless stream of cooking power.
A traditional microwave only has two power output levels, fully on and fully off. Intermediate heat settings are achieved using duty-cycle modulation and switch between full power and off every few seconds, with more time on for higher settings.
An inverter type, however, can sustain lower temperatures for a lengthy duration without having to switch itself off and on repeatedly. Apart from offering superior cooking ability, these microwaves are generally more energy-efficient.
As of 2020, the majority of countertop microwave ovens (regardless of brand) sold in the United States were manufactured by the Midea Group.
The Galanz lags at heating speed and may try your patience, but once it gets going, it heats evenly and operates quietly. And it earns a Very Good rating for defrosting. Plus it looks good and the price is right.
A powerful, yet small microwave oven and broiler in one! The 2-in-1 Microwave Oven with FlashXpress Broiler (NN-GN68KS) is a multi-use kitchen appliance that makes cooking delicious family meals and snacks a breeze. Now you can broil with grill-like results using the FlashXpress Broiler, or use as a microwave to cook, defrost, and reheat food quickly and easily using smart cooking technology.
This Panasonic 1.20 cubic-foot 1200 -watt microwave oven has the following:
a sensor
auto-defrost
touchpad controls
Heating evenness and speed of heating are superb, and it defrosts very well, too, earning a Very Good rating. The controls are self-explanatory, and this machine operates relatively quietly. It’s another model that comes equipped with a sensor, which takes the guesswork out of cooking.
The well-priced Panasonic NN-SN946W has a lot going for it. This large microwave aces three of tough tests: speed of heating, heating evenness, and defrosting evenness. It runs quietly. This model is equipped with a sensor that shuts off the oven once the food is hot enough.
This GE PVM9005SJSS is a good choice for a busy household. It earns an Excellent rating in heating evenness test, in which we reheat a dish of cold mashed potatoes. Speed of heating is also top-notch, and it operates quietly.
If you tend to take something out of the freezer to make for dinner when you get home from work, the KitchenAid KMHS120ESS is a good bet. It earns an Excellent rating on defrosting test, in which we defrost a pound of ground chuck. It also aces the heating evenness test and is very quiet. It has a cooking sensor and comes with a rack, in case you want to cook two dishes at once.
The LG LMV2031ST is a good choice if you use your microwave to cook and not just for reheating and defrosting. It fits a 9×15-inch baking dish and has a wire rack, allowing you to cook two dishes at once. It’s equipped with a sensor that turns the microwave off to keep you from overheating your food. This model earns Very Good ratings for speed of heating and heating evenness.
The LG LMH2235ST is a good choice if you often find yourself having to defrost something straight out of the freezer; it earns an Excellent rating in defrost test. It’s impressive at heating foods quickly and evenly, too. Plus, this microwave is one of the quietest models. It has a sensor to prevent you from overheating your food and a rack in case you want to cook more than one dish at the same time.
A top performer from Whirlpool, the WMH53521HZ earns an Excellent rating in heating evenness test, meaning a dish of cold mashed potatoes has few or no cold spots after microwaving. It has a cooking sensor that helps estimate how much time and power you’ll need for each dish, and it fits a 9×15-inch dish, so you can cook a casserole. This microwave is very easy to use.
Microwave ovens transfer heat more efficiently by directly heating up the water in the food. This heat energy transfer rate is about 30% to 80%. On a stove top, the heat transfer time from the burner is much less — 12 to 14 percent of the heat energy goes into the food you’re cooking.
In addition, the quality and type of cookware you use also determines the rate of heat transfer. What you’re cooking also effects cook time.
source: en.wikipedia.org– plus100years.com– consumerreports.org– galanz.com– panasonic.com– kitchenaid.com– lg.com– whirlpool.com– directenergy.com
Related Post
Parsaland Trading Company with many activities in the fields of import and export, investment consulting, blockchain consulting, information technology and building construction
