Aren’t you curious about how heat spreads? Did you think about what exactly happened when you touched something hot?
Heat transfer is separated into three sections. Heat can be transferred from a warmer to cooler object by conduction, convection, and radiation. Each of the various types are similar and different in many ways.
To start out, convection is heat transfer through a fluid (liquid and gas). Convection happens when a fluid is heated. The part nearest the heat source expands. The kinetic energy increases as molecules move faster and contract. The heated fluid becomes less dense. Density is the amount of mass in a volume. The fluid is forced to rise because it is less dense than the cooler, more compact fluid. When it reaches the surface, the warmer liquid starts to diffuse and expands to the sides. At the surface, it cools down and the fluid sinks. The heat source then reheats the liquid. The liquid then goes over the same process over and over again. These are called convection currents. Convection currents continue until the heat source has been removed and the molecules are the same temperature. Convection currents are a chain of movement by heat through a liquid when there is a heat source. Unlike radiation, convection can be visible sometimes. Convection, along with radiation and conduction happen near earth’s surface. Convection, conduction and radiation all involve a heated object. Convection does not transfer heat through electromagnetic waves. Some examples of convection are in the asthenosphere, troposphere, and even at homes. In the asthenosphere (a layer between 100-200 miles below the earth’s crust, right above the mantle) the magma in the asthenosphere which is nearest the mantle rises because it is heated by the mantle. Once it reaches the top, it expands to the sides, the fluid sinks, the fluid gets heated again. Convection causes more warming than radiation and conduction in the troposphere (the lowest layer of atmosphere). The air near the ground gets heated and the molecules have more kinetic energy. They crash into each other and expand farther out. When it moves farther out, it becomes less dense. The cooler more dense air stays at the bottom, while the warmer flows into the troposphere. Some home appliances
that involve convection are heaters and refrigerators. Heaters are a combination of both convection and radiation. The heater sends out electromagnetic waves which is radiation. The heat which escapes from the heat sources is force to rise because it is less dense than the cooler air around it. At the top of the house, it expands towards the sides, it starts to cool, and then it sinks as the heater heats the air again. Refrigerators
use convection currents in order to stay cool. There is a heat absorber on the bottom and a cooler on the top. The warmer air rises through narrow tube and it goes to the cooler on the top. Once it cools, it goes through an open place where the food is. It cools the food as the cool air sinks down. It is then heated again and continues in the repeating cycle again and again.
In addition, radiation is another way of heat transfer. Radiation is the transfer of heat in contact with electromagnetic waves through an empty space. Unlike radiation and convection, radiation does not involve direct contact between molecules. Radiation is the only form of heat transfer which can cross a vacuum
(a space which is empty of matter).It is also the only form of heat transfer which transfers by waves. There are many types of radiation. One is infrared radiation. Infrared radiation travels directly to an object. Infrared radiation causes the greatest temperature increase. Examples of infrared radiation is heat from the sun, heaters, lamps, light bulbs, etc. The sun’s radiation is mostly made out of visible light radiation and infrared radiation. A small portion is also made out of ultraviolet radiation, a very dangerous type of radiation. An effect which infrared radiation causes is the greenhouse effect. When heat enters a space, only 50 percent of the heat can escape. This is the cause of global warming.
Furthermore, conduction is another form of how heat can be transferred. Conduction is heat transfer by direct contact within particles of matter. Conduction can only be transferred through solids unlike convection. The energy nearest the heat source increases, the particles start vibrating and spread on some of their energy, spreading heat through the whole solid. Unlike radiation, conduction needs direct contact with particles. Both conduction and convection need matter to transfer heat. Metals
are good conductors because they have freely moving electrons which pass energy more efficient. Substances that conduct heat slowly are called insulators. Wood and water are examples of insulators. An example of conduction uses a pan, some water, and a metal spoon. Once after some time, the metal spoon gets heated by conduction because particles near the bottom vibrate faster when they are heated, they bump into cooler molecules. Eventually, the whole spoon heats up. Another example of conduction is the desert. The sun heats up the top layer of sand on the desert, so it becomes extremely hot. When someone steps on the sand, conduction transfers some of the heat to the barefoot of the person. When someone is wearing a leather shoe, it is a better insulator then a regular foot so it takes longer for it to heat up. The molecules gain energy every time they pass some energy to nearby molecules. The ability to transfer heat within an object is called thermal conductivity.
Clearly, conduction, convection, and radiation are the ways heat can be transferred from warmer to cooler object. The three types of heat transfer each have their very own unique characteristics. The type of heat transfer will vary because of the substance (fluid or solid) and how heated is transferred.
