Conductivity is the ability of a body or material to transmit heat. At the same time, it moves through a solid object or from one object to another, because both of them are in contact with each other. This is the only way heat can pass through the body. The question arises: "How does air and other materials conduct heat?" Find out in the article!
Thermal conductivity
The ability to transfer heat inside an object is called thermal conductivity. This property is denoted by the letter k, and is measured in W / (m ร K). Thermal conductivity values โโvary for different materials. So, gold, silver and copper have high thermal conductivity. By the way, these materials are also good conductors of electricity. How does air conduct heat? The answer is short: he is a poor conductor. The high conductivity of gold, silver and copper is due to the fact that the electrons that are responsible for charge transfer also take part in the transfer of thermal energy.
But materials such as glass and mineral wool have low thermal conductivity. This is explained by the fact that they have very few โfreeโ electrons for the transfer of thermal energy inside a solid. Materials of this type are called insulators. The heat transfer rate (that is, the speed of movement of thermal energy) directly depends on the thermal conductivity, the temperature difference and the contact area and the material that the body possesses. For the same reason, it cannot be argued that air conducts heat well.
If the material is a good conductor of heat, then it quickly moves through the body. Metals are widely used for heat transfer because they have properties that allow heat to be distributed while at the same time withstanding the extreme temperatures associated with heating.
It is electrons that are responsible for the transfer of thermal energy, as well as electric charge. Therefore, metals are good conductors of heat and electricity! Here lies the answer to the question: โWhy does air conduct heat poorly?โ
Nevertheless, you should not confuse the electrical conductivity (which is associated with the charge of electrons) when you mean thermal conductivity (which is associated with the transfer of electron energy).
We prove empirically
Try to hold one end of the metal rod over the flame - after a few minutes it will heat up.
Now hold the end of the wooden stick in the flame, and this end will become so hot that it will eventually light up completely. However, the end of the stick that you hold onto will remain relatively cool.
Heat does not spread throughout the body because of its composition: its structure makes it difficult for electrons to transfer heat through the material.
Thus, everyday experience indicates that wood is not a good conductor of heat. If you ever had to see a section of a tree under a microscope, then you probably noticed the peculiarities of the structure of wood: it consists of separate cells that act as insulators, because they are not interconnected. Cells are scattered like stones in a stream. On this material, heat moves much more slowly than in metals, where atoms are bonded to each other in a three-dimensional โlatticeโ.
Air does not conduct heat well. The experience of everyday life shows: remember the structure of the windows. They always consist of at least two glasses between which there is an air "pillow". This layer helps to keep heat in the room without letting it out.
So, if thermal energy is applied directly to one part of a solid object, the electrons in the object become excited. This leads to vibrations of the atomic lattice, which pass through the object, increasing the temperature during passage. The closer the links inside the solid, the faster the heat transfer.
Liquids - Bad Heat Conductors
If you fix an ice cube at the bottom of a test tube with water (you need to use weight to do this, otherwise it will float on the surface, because ice has a lower density than water), and then heat the water at the top of the tube, you find that the water will boil at the top of the tube and the ice cube will remain frozen.
This is due to the fact that water is a poor conductor of heat. Most of the heat will move in the convection current inside the water at the top of the tube, only a small part of it will sink to the ice cube.
How does air conduct heat?
Air is a collection of gases. Although it is great for convection, the amount of heat that it can transfer is minimal, because the small mass of the substance cannot store a large amount of heat - which is why it is not considered a good conductor. The insulating properties of air are used by mankind in everyday life. So, they are used to isolate coolers in the walls of the building. Even the work of a thermos is based on the fact that the air does not conduct heat well. There really are plenty of examples!
So what is the reason for this phenomenon? Since the air is loose, there is a certain mass available to transfer thermal energy through conductivity. Therefore, it is a poor conductor, but an excellent insulator. Nevertheless, the answer to the question: โDoes the air conduct heat?โ - not so straightforward. So, consider the following phenomena.
Radiation is the transfer of energy through waves or excited particles. Air creates a thermal gap that does not allow thermal energy to be overcome above it. Heat must be radiated from the surface to the air particles, then it must be radiated from the air to the opposite surface. Heat moves very slowly between the three materials, and most of the transferred heat energy is absorbed in the air.
Convection is the movement of heat through a liquid or gas due to a decrease in density due to heat absorption. In this case, the properties of air become extremely useful. It also moves upward, transferring heat from an insulated container or space. Therefore, convection is used to remove heat and can be used to cool the surface. The distribution of heat through convection in air is somewhat inefficient, but it is used for many cooling purposes. Yes, air does not conduct heat well.
Insulation Examples
Insulation is used for many purposes. Some of them include cooling drinks and food products, creating air gaps in walls, introducing air cavities into kitchen utensils. The features of how air conducts heat are applied even in insulating foam.
Output
Conductivity is the passage of heat through a solid. It differs from the phenomenon of convection in that in the process there is no movement of matter. Now we know whether the air conducts heat well, and also what causes it.