Common conduction is divided into heat conduction and electric conduction.It refers to the transfer of heat or electricity from one part of an object to another.
Heat is transferred from the higher temperature part of the object to the lower temperature part along the object, which is called heat conduction.Conduction isheat transferOne of the three modes of (conduction, convection and radiation).heat conductionIt is the main mode of heat transfer in solids.In gas or liquid,heat conductionThe process often occurs simultaneously with convection.All kinds of materials can conduct heat, but different materials have different heat transfer abilities.
Chinese name
conduction
Foreign name
conduction
Discipline
thermodynamics
Meaning
Heat transfer from high temperature to low temperature
Heat transfer from high temperature zone to low temperature zone without material transfer.Heat conduction originates from the transfer of kinetic energy generated by the collision between atoms and molecules in gases, liquids and non-metallic solids.Metal is a good thermal conductor and electrical conductor. Energy in metal is transferred by collision between free electrons passing through crystal lattice and ions in lattice.
Also called heat conduction, it is one of the three basic ways of heat transfer.The main way of heat transfer in solids is to transfer heat from a higher temperature part of an object to a lower temperature part or to another object with a lower temperature in contact with it by means of the collision of molecules, atoms or electrons in the object.In liquid or gas, it is often carried out simultaneously with convective heat transfer.All objects have heat conduction as long as there is a temperature difference, regardless of whether there is relative motion between particles inside or not.In industry, there are many heat transfer processes mainly based on heat conduction, such asRubber productsHeat vulcanization, heat treatment of steel forgings, etc.Design calculation of kiln, heat transfer equipment and thermal insulation, high temperature and high pressure equipment (such asWaste heat boilerThe heat conduction law shall be used in the design.[1]
Electric conduction
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The movement of electricity through matter.In a good conducting metal, electrical conduction originates from the migration of free electrons moving in one direction under the influence of an electric field.In liquid conductors, electrical conduction is due to the migration of positive ions in one direction and negative ions in the opposite direction.In a gas, electrical conduction occurs because positive ions flow in one direction and electrons flow in another.In semiconductors, electrical conduction originates from the migration of electrons in one direction and of positrons in the other.
Conductive medium
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Materials good at heat transfer are called good heatconductorA substance that is not good at heat transfer is called a bad conductor of heat.All kinds of metals are good conductors of heat, among which silver is the most good at heat transfer (gold has better heat transfer and conductivity, and most computer CPUs on the market now contain gold), followed by copper and aluminum.Porcelain, paper, wood, glass and leather are all bad conductors of heat.Wool, feather, fur, cotton, asbestos, cork and other soft materials are the least good at heat transfer.Liquid, except mercury, is not good at heat transfer, and gas is not good at heat transfer than liquid.feverCableA part of the temperature is transmitted to the ground by conduction.
Physiological conduction
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It refers to the process of excitation spreading around the cell membrane.Cardiac myocyteThe cytoplasm and extracellular fluid of the cells are both good conductors, and the cell membrane between them has greater resistance to current.Since the electric resistance of the cell membrane is greater than that of the cytoplasm and extracellular fluid, the current will advance along the cell membrane, and the fibers of the conduction system will flow out longitudinally from any excited point.The heart is not composed of syncytial cells, but of innumerable cardiac myocytes. Each cardiac myocyte has a complete cell membrane, and the two cells are separated at the intercalated disk.Therefore, the spread of excitement in the heart muscle is from one cell to another.Although myocardial cells are separated by cell membrane, there are some connections in some parts of the membrane to connect them together, among which gap junction is a hydrophilic channel connecting two adjacent cells.Gap junction is formed on the membrane where two cells are close to each other, each free hexagonal subunit is connected with each other, and the center is a hydrophilic channel.Through gap connection, chemical substances can be freely exchanged between adjacent cells, which is called "chemical coupling";The potential change of one cell can affect the corresponding potential change of adjacent cells, which is called "electric coupling".Electrical coupling plays a leading role in the conduction of cardiac myocyte impulses, while chemical coupling also has a certain impact on cell excitability by transporting bioactive substances.The cable property of myocardial cell membrane promotes the conduction of action potential.After depolarization, one cell becomes the power source, which makes the membrane polarity of adjacent cells reverse and depolarization occurs. Then, the same process affects the third myocardial cell, and so on, until all myocardial fibers are depolarized.The impulse conduction process is realized by local current, and is related to the rising speed and amplitude of action potential phase 0 after cell depolarization.Only excitations with large depolarization velocity and amplitude of phase 0 can cause conduction.In addition, conduction is also related to the diameter of myocardial cells, membrane capacitance and membrane resistance.Both cardiac conduction system and myocardial tissue have conduction properties.Therefore, the conduction process of excitation from the sinoatrial node to the ventricular muscle along the internodal bundle, atrial muscle, atrioventricular junction area, Purkinje fiber and ventricular muscle is actually the process of action potential generated by the sinoatrial node conducting sequentially through a series of conduction tissues and myocardial cells.[2]
