Using the information from the text, write a short summary.
Text 1
Radiant heating is a method of equalizing temperature within a room. A continuous loop of hot-water pipe electric cable is installed in the ceiling or floor. Heat leaves the pipe or cable by radiation, which does not directly raise the temperature of the air within a room. Radiation affects only the objects it strikes, and so it produces more uniform heating than convection does. Radiant heat provides comfort at a lower room temperature than other heating systems. Radiant heating may also be installed along the baseboards of a room. One system uses a metal shield about 6 inches (15 centimeters) high to cover a hot-water pipe that runs close to the floor. Such a system distributes heat evenly. All radiant heating systems limit the temperature difference between the floor and the ceiling to only a few degrees.
Electric heating differs from other central systems because it requires no combustion of fuel in the building being heated. The fuel used to make electricity is burned at an electric power plant that may be far away. Nuclear plants produce electricity from nuclear energy.
Electric heat is produced by electric heating units. Such units produce heat by passing electricity through a material that resists the flow of current. This type of heating, called resistance heating, produces much radiant heat. Such heat warms the surface of the skin and clothing and makes people feel comfortable even in a cool room. An electric heating unit can be placed in the ceiling, baseboards, floor, or wall. The temperature can be controlled by thermostats in each room, or area.
Heat pumps. Even in cold weather, the earth or outside air contains heat that can be used to heat a building. A mechanical system called a heat pump takes heat from the outside air arid brings it inside. In winter, a heat pump circulates a liquid refrigerant through a coil outside the building. As the cold liquid passes through the coil, it picks up heat from the outside air or earth and becomes a vapor. The vapor then passes into a compressor. The compressor increases the temperature and pressure of the vapor. Then the hot vapor passes through an inside coil, where it heats the air. In the process, the vapor condenses into a hot liquid. The hot liquid then goes through a pressure-reducing valve and becomes cold again. Finally, the refrigerant is forced back to the outside coil and the cycle begins again.
In cold regions, a heat pump may not be able to supply all the necessary heat economically. In such places, electric resistance heating units provide additional heat on the coldest days. During the summer, a heat pump reverses its operation. It cools the building by pumping heat from the inside to the outside.
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Text 2
Furnace is a device in which heat is produced. Some furnaces heat the air in people's homes. Others produce steam to run electric power plants. Furnaces are necessary in the manufacture of iron and steel, glass, pottery, and other products. They also are used in petroleum refining. This article deals with both industrial and home heating furnaces. For further information on home heating systems, see the article on Heating.
Furnaces range in size from kitchen ovens to the huge furnaces used in steel production. Most industrial furnaces are built of refractory (heat-resistant) bricks, which are able to withstand great variation in temperature without weakening. The walls and roofs of some modern furnaces are made of refractory fiberglass cloth that is mounted on metal frames. The combustion chamber in most home heating furnaces is made of steel.
Sources of heat. Most furnaces generate heat by burning fuel. These furnaces are called combustion fur-laces. Early combustion furnaces burned wood or charcoal. During the 1600s, coal began to replace these fuels. During the mid-1900s, many industrial furnaces were converted to burn oil. Today, most industrial combustion furnaces burn natural gas. This fuel causes almost no air pollution. Natural gas also is easy to control. A home heating furnace is a type of combustion furnace. Gas piped into a combustion chamber mixes with air drawn in from around the furnace. This gas-air mixture burns. A blower draws n a separate stream of cool air and pushes it around the chamber. Heat from the chamber warms this air before it travels to the rooms. A typical furnace has four combustion chambers.
Heating the charge. There are two basic types of furnaces, based on the way they heat a charge: (1) batch furnaces and (2) continuous furnaces.
Batch furnaces heat materials singly or a group at a time. Clay pots, for instance, are baked in batches in kilns (ovens). After baking, all the pots are removed before the next batch is placed in the kiln.
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Handling the hot charges is often a problem in batch processing because of the high temperatures required in industrial furnaces. A number of solutions have been developed. Workers use steel tongs to remove small articles from batch furnaces, and large mechanical arms and cranes handle larger items. In a car bottom furnace, a type of batch furnace, the floor and door are on wheels and can be pulled out like a drawer to reach the charge. A top hat furnace can be lifted off its base to be loaded or unloaded. Batches of steel and copper are heated in large pot furnaces. Once the materials are melted, the whole furnace is tilted and the glowing hot liquid pours out a spout.
Continuous furnaces heat a steady flow of material that passes through them. This material may be rolled through the furnace on carts, pushed through by hydraulic rams, or carried on conveyor belts. Crude oil and water pass through furnaces in pipes. Some furnaces rely upon gravity to move the material through them. For example, iron ore is fed in at the top of a blast furnace, and molten iron flows out from the bottom. Cement is produced by roasting crushed limestone in a rotary kiln, a slightly inclined, long steel tube lined with refractory brick. The pieces of limestone are fed in at the higher end and slowly tumble to the lower end as th
work. But as a system does work, its entropy increases until the system can no longer perform work.
The third law of thermodynamics concerns absolute zero. It states that it is impossible to reduce the temperature of any system to absolute Zero.
Heat pipe is a device that transfers large amounts of heat from one place to another with only small amounts of heat loss. Heat pipes can transport much more heat per unit area than the best metal conductors, including copper and silver. Unlike most heat transfer devices, they require no external power source. This feature makes them more energy-efficient and more economical.
Heat pipes are used to remove waste heat from certain types of electronic equipment and industrial machinery. In many cases, they carry this heat to another place where it can be used. Some air-conditioning and heating systems employ heat pipes to regulate temperature. Heat pipes also have been used for such purposes as controlling the temperature in spacecraft and transporting heat from solar energy collectors.
A heat pipe consists of a metal tube that is sealed at both ends and lined with a porous material. The lining,
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