Conduction, convection, and radiation are the three forms of heat transfer. Heat is the energy that passes from one body or system to another.
Heat transfer only occurs when there is a temperature difference between two things.
In drivingheat transfer occurs when a body or object is in contact with another.
convectionInstead, it is produced by the movement of gases or liquids at different temperatures.
For his part, the radiation It is a transfer of heat without the bodies being in contact. Therefore, this is given by the emanation of energy through electromagnetic waves.
An example that illustrates this would be that of a pot of boiling water: the fire heats the pot (radiation), the metal of the pot heats the water (conduction) and the hot water rises due to the heat (convection).
Conduction Convection Radiation Definition Form of heat transfer by contact. Form of heat transfer by movement of matter. Form of heat transfer by electromagnetic waves. Direction of transfer From high to low temperature Mechanism Movement of atoms within a body Movement of gases and liquids due to temperature difference Propagation of electromagnetic waves in space Examples The handle of an aluminum pot on a burning stove Domestic heating systems The hot of the sun
What is heat conduction
Ice melts by conduction of heat from the hand.
Conduction is a form of heat transfer that occurs when two bodies are in contact or when heat passes from one side of the same body to the other. For example, if we heat one end of an iron rod, the other end will heat up after a while, despite not being in direct contact with the heat source.
The conduction heat transfer mechanism is based on the movement of atoms. As the temperature rises, the atoms move faster and also push on neighboring atoms, transferring heat to them.
The ability of materials to conduct heat is known as thermal conductivity. For example, air has a low conductivity as well as wood.
On the other hand, metals, such as aluminum and iron, have high thermal conductivity. These materials are very effective in conducting heat, since they have free electrons that transfer energy faster from hot areas to cold areas of the body.
Examples of heat conduction
Cast iron skillet on a lit burner: Heat from the burner heats the pan which conducts heat to the rest of the pan and the contents within it.
melted ice in hand: If we place ice in our hand, it melts due to the conduction of body heat.
warm feet in the sand: on a hot day at the beach, if we walk on the hot sand with our bare feet, after a while we will feel that we are burned by the conduction of heat from the sand to our feet.
The cup of hot coffee: When pouring hot coffee (or other hot drink) into a cup, we will eventually feel the heat in our hands. That’s why the cups have a handle so we can grab it without burning ourselves.
The ironing of clothes: The iron used to remove wrinkles from clothes gets hot and when it comes into contact with clothes, it conducts heat.
The thermometer: This instrument is used to measure temperature because it receives or transfers heat by conduction from the object or substance with which it is in contact.
The metal spoon vs. the wooden spoon: a wooden spoon conducts heat poorly while a metal spoon heats up quickly. That’s why we can mix the food with the wooden spoon, but when we eat the soup we use the metal spoon.
What is heat convection
Hot air balloons float due to the lower density of hot air. This occurs due to convection.
Convection is the form of heat transfer that is produced by the movement of liquids and gases from hot areas to cold areas. When a fluid is heated, it becomes less dense, which causes it to rise.
It is thanks to the convection process that clouds are formed: water vapor and hot air on the Earth’s surface rise to later condense as clouds in the heights. This type of convection is natural or free, without the intervention of external forces.
On the other hand, forced convection occurs when a force is applied to move the fluid. This is what happens when we use fans to move hot air around a room, or when we move the contents of a pot on the stove.
Examples of heat convection
Domestic heating systems: the air in contact with a heating system heats up, then rises and displaces the cold air, causing drafts.
Earth’s internal heat: The Earth’s core is hot and fluid, so convection currents are produced that cause earthquakes and volcanic eruptions.
The fluid in the thermos accumulators: In the pipes of a solar heater, the fluid heats up and becomes less dense, moving the heat to the cooler fluids.
convection oven: The hot air inside the oven is circulated by a fan, which makes the food bake more evenly.
boiling water in a pot: when we put water in a pot on a lit stove, the hot water from the bottom rises, forcing the movement of the cold water from the surface.
Hair dryer: cold air enters the dryer, it is heated by passing through a resistance and hot air is blown through the nozzle.
ocean currents: the waters of the oceans are kept in constant movement by convection, the warm water of the tropics moves towards the poles.
hot air balloons or hot air balloons: by heating the air, it becomes less dense, it is trapped inside the balloon fabric, causing it to float. For this reason, to go down, a window opens that lets the hot air escape.
What is heat radiation
A candle flame emits heat by radiation.
Radiation is the transfer of heat without contact between objects. This occurs through electromagnetic waves, such as visible, ultraviolet, and infrared light, which propagate through space. The presence of material is not required for the radiation of heat to occur.
Bodies emit heat by radiation, but they also absorb heat, depending on the temperature difference. In fact, the bodies that best absorb are also good emitters. For example, a black surface absorbs radiation better, but it also emits more than a white surface.
Thus, the emission depends on the body temperature, the higher the temperature, the greater the heat emission.
The operation of a thermos is based on concentrating heat radiation inside. A thermos is built with a double glass wall with no air between them, to prevent heat loss by conduction or convection. The silver inner wall reflects radiation without absorbing it, so the drink stays hot longer.
Examples of thermal radiation
The heat of the sun: The Earth receives heat from the Sun by radiation.
hot sand on a beach: on a summer day solar radiation heats the sand.
embers of a bonfire: when we approach a bonfire or fireplace, the burning coals give off heat by radiation.
Solar Furnace: the sun’s rays fall on a surface heating the air.
Infrared thermometer: measures the radiation of a body in the infrared range and represents it as temperature.
thermal cameras: Thermal imaging cameras record the heat of bodies emitted by radiation.
tanning beds: tanning beds are based on the emission of ultraviolet rays that promote the tanning of the skin. Its use is limited by the predisposition to skin damage.
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