Principles of rotating equipment pdf

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Microwave ovens are a common kitchen appliance and are popular for reheating previously cooked foods and cooking a variety of foods. They are also useful for rapid heating of otherwise slowly prepared foodstuffs, which can easily burn or turn lumpy when cooked in conventional pans, such as hot butter, fats, chocolate or porridge. Microwave ovens have a limited role in professional cooking, because the boiling-range temperatures of a microwave will not produce the flavorful chemical reactions that frying, browning, or baking at a higher temperature will. However, additional heat sources can be added to microwave ovens. The exploitation of high-frequency radio waves for heating substances was made possible by the development of vacuum tube radio transmitters around 1920. 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. Sir Henry Tizard travelled to the U. In 1945, the specific heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. In 1947, Raytheon built the “Radarange”, the first commercially available microwave oven. 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.

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In the 1960s, Litton bought Studebaker’s Franklin Manufacturing assets, which had been manufacturing magnetrons and building and selling microwave ovens similar to the Radarange. Litton then developed a new configuration of the microwave: the short, wide shape that is now common. 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”. Formerly found only in large industrial applications, microwave ovens increasingly became a standard fixture of residential kitchens in developed countries. Adoption has been slower in less-developed countries, as households with disposable income concentrate on more important household appliances like refrigerators and ovens. A microwave oven heats food by passing microwave radiation through it.

Microwave heating is more efficient on liquid water than on frozen water, where the movement of molecules is more restricted. C, dielectric loss is greatest at a field frequency of about 10 GHz, and for higher water temperatures at higher field frequencies. Microwave heating can cause localized thermal runaways in some materials with low thermal conductivity which also have dielectric constants that increase with temperature. An example is glass, which can exhibit thermal runaway in a microwave to the point of melting if preheated. Additionally, microwaves can melt certain types of rocks, producing small quantities of synthetic lava.