Vacuum bottle. Vacuum cleaner

Vacuum bottle is a container that keeps liquids hot or cold for many hours. It is also called a Dewar flask or a Thermos bottle, which is the trademark for a brand of vacuum bottle produced by the Thermos Company. Vacuum bottles vary widely in size, ranging in capacity from 2 ounces (59 milliliters) to 15 gallons (57 liters). They are commonly used to carry coffee, juice, milk, or soup. Some types of vacuum bottles are used in scientific work to store chemicals and drugs, to transport tissues and organs, and to preserve blood plasma.

Sir James Dewar, a British chemist, invented the vacuum bottle in 1892. He developed it for storing liquefied gases. Although his flask was designed to prevent the entry of heat from outside the container, it worked equally well in keeping liquids hot by reducing the loss of heat from the inside.

The modern vacuum bottle has the same basic design as Dewar's flask. It blocks the three processes through which heat is transferred—conduction, convection, and radiation (see Heat [How heat travels]). A typical vacuum bottle has an inner container that consists of two glass or stainless steel bottles, one within the other. Glass and stainless steel do not transmit heat well, and so they reduce heat transfer by conduction. The inner and outer bottles are sealed together at their lips. Most of the air between the bottles is removed to create a partial vacuum.

This vacuum hinders heat transfer by convection because it has few air molecules to carry heat between the bottles. The facing surfaces of glass bottles are coated with a silver solution. They act like mirrors and reflect much of the heat coming from inside or outside the container. In doing so, they prevent heat transfer by radiation. In stainless steel vacuum bottles, a layer of copper foil between the inner and outer bottles serves the same purpose.

Other features of vacuum bottles help minimize both the loss or entry of heat. Most vacuum bottles have a small mouth, which reduces heat exchange. The bottles are closed with a stopper made of cork, plastic, or some other material that conducts heat poorly. The inner container of a vacuum bottle is encased in metal or plastic.

A rubber collar around the mouth holds the inner container in place, and a rubber cushion at the base serves as a shock absorber.

A vacuum bottle is two bottles in one, as shown here. A vacuum in the space between the inner and outer bottles helps prevent heat from passing through the bottle

Vacuum cleaner is an electric appliance that cleans by suction. Vacuum cleaners remove dirt and waste material from carpets, rugs, and bare floors. They may also be used to remove dust and dirt from furniture, woodwork, curtains, and other above-the-floor items. The first vacuum cleaning devices were developed about 1900.

The two main kinds of vacuum cleaners are the canister and the upright In a canister, above, a suction fan pulls dirt through a hose and into a bag. In an upright, below, a suction fan draws in waste material that has been loosened by an agitator, a rotating cylinder with bristles

A vacuum cleaner works by means of a suction fan, which creates a partial vacuum within the machine. Outside air, which always tries to fill a vacuum, flows rapidly into the cleaner, drawing in dirt. A cloth or paper bag, or other container, traps the dirt, and the cleaned air is blown out of the machine. The container must be emptied or changed regularly.

There are two main kinds of portable vacuum cleaners: (1) canisters, or tanks, and (2) uprights. In a canister model, a powerful suction fan pulls dirt into the bag through a hose to which a variety of nozzles can be attached. An upright model has a small fan and an agitator in its base. The agitator is a rotating cylinder with bristles that loosen dirt Waste is sucked into a bag attached to the machine's handle. Combination vacuum cleaners combine various features of canisters and uprights.

Other types of portable vacuum cleaners include handheld and utility vacuum cleaners. A handheld model can be held in one hand and is used primarily for above-the-floor cleaning. A utility vacuum cleaner is a type of canister used to pick up large particles of dirt Some utility models are designed to pick up liquid.

Stationary or built-in vacuum cleaners are called central vacuum cleaners. They have various kinds of nozzles and a hose that connects to a special fitting on the wall. Dirt moves from the hose through a network of ducts to a remotely located dirt-collecting system.