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Answer: The transfer of heat is through heated solid substance, in conduction, whereas in convection the heat energy is transmitted by way of intermediate medium. As the layers of earth transfer the heat of the core through conduction, the earth may have warmer or cooler patches. The difference in temperature causes a convection current and may affect fault lines, causing earthquakes.
Convection currents describe the rising, spread, and sinking of gas, liquid, or molten material caused by the application of heat. Tremendous heat and pressure within the earth cause the hot magma to flow in convection currents. Convection works by areas of a liquid or gas heating or cooling greater than their surroundings, causing differences in temperature.
These temperature differences then cause the areas to move as the hotter, less dense areas rise, and the cooler, more dense areas sink.
As the core heats the bottom layer of mantle material, particles move more rapidly, decreasing its density and causing it to rise. It eventually becomes cool and dense enough to sink back down into the mantle. Begin typing your search term above and press enter to search. Press ESC to cancel. The thermal conductivity is dependent upon the nature and dimensions of the heat transfer medium. All heat transfer problems involve the temperature difference , the geometry , and the physical properties of the object being studied.
In conduction heat transfer problems, the object being studied is usually a solid. Microscopically this mode of energy transfer is attributed to free electron flow from higher to lower energy levels, lattice vibration and molecular collision. Consider a block of stone at high temperature, that consists of atoms that are oscillating intensely around their average positions. At low temperatures , the atoms continue to oscillate, but with less intensity. If a hotter block of stone is put in contact with a cooler block, the intensely oscillating atoms at the edge of the hotter block gives off its kinetic energy to the less oscillating atoms at the edge of the cool block.
In this case there is energy transfer between these two blocks and heat flows from the hotter to the cooler block by this random vibrations. The modern view is to ascribe the energy transfer to lattice waves induced by atomic motion. In an electrical insulators, the energy transfer is exclusively via these lattice waves. In a conductor, it is also due to the translational motion of the free electrons. Heat transfer processes can be quantified in terms of appropriate rate equations.
This law states that the time rate of heat transfer through a material is proportional to the negative gradient in the temperature and to the area, at right angles to that gradient, through which the heat flows.
Its differential form is:. Although liquids and gases are generally not very good conductors of heat, they can transfer heat quite rapidly by convection. Convection takes place through advection , diffusion or both. Convection cannot take place in most solids because neither significant diffusion of matter nor bulk current flows can take place. Diffusion of heat takes place in rigid solids, but that is called thermal conduction. The process of heat transfer between a surface and a fluid flowing in contact with it is called convective heat transfer.
In engineering, convective heat transfer is one of the major mechanisms of heat transfer. When heat is to be transferred from one fluid to another through a barrier, convection is involved on both sides of the barrier.
In most cases the main resistance to heat flow is by convection. Convective heat transfer take place both by thermal diffusion the random motion of fluid molecules and by advection, in which matter or heat is transported by the larger-scale motion of currents in the fluid. Heat transfer by convection is more difficult to analyze than heat transfer by conduction because no single property of the heat transfer medium, such as thermal conductivity , can be defined to describe the mechanism.
Convective heat transfer is complicated by the fact that it involves fluid motion as well as heat conduction. Heat transfer by convection varies from situation to situation upon the fluid flow conditions , and it is frequently coupled with the mode of fluid flow. Immediately: The ice without chain floats near the surface of Beaker B The ice with chain sinks to the bottom of Beaker A.
After few minutes: In Beaker A, the cold, colored water remains near the bottom of the beaker, and hot clear water stays near the top In Beaker B, the dyed water melted from the ice quickly starts sinking down and warmer water from the bottom of the beaker rises to replace it. After 30 minutes: The ice is still largely unmelted at the bottom of the beaker A. Just above the surface of the ice, there is a small layer of colored water.
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