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The flow of heat is a form of energy transfer. Heat transfer is the natural process of moving energy to or from a system, other than by work or the transfer of matter. In a diathermal system, the internal energy can only be changed by the transfer of energy as heat: =.
In this framework, the LAB separates the two heat transport regimes [conduction vs. convection]. [5] However, the transition from a domain that transports heat primarily through convection in the asthenosphere to the conducting lithosphere is not necessarily abrupt and instead encompasses a broad zone of mixed or temporally variable heat transport.
A heat current or thermal current is a kinetic exchange rate between molecules, relative to the material in which the kinesis occurs. It is defined as the net rate of flow of heat . The SI unit of heat current is the watt , which is the flow of heat across a surface at the rate of one Joule per second.
Thermal conduction is the diffusion of thermal energy (heat) within one material or between materials in contact. The higher temperature object has molecules with more kinetic energy ; collisions between molecules distributes this kinetic energy until an object has the same kinetic energy throughout.
For a closed system (transfer of matter excluded), the heat involved in a process is the difference in internal energy between the final and initial states of a system, and subtracting the work done in the process. [2] For a closed system, this is the formulation of the first law of thermodynamics.
The relationship between thermal conductance and resistance is analogous to that between electrical conductance and resistance in the domain of electronics. Thermal insulance (R-value) is a measure of a material's resistance to the heat current. It quantifies how effectively a material can resist the transfer of heat through conduction ...
The law is frequently qualified to include the condition that the temperature difference is small and the nature of heat transfer mechanism remains the same. As such, it is equivalent to a statement that the heat transfer coefficient, which mediates between heat losses and temperature differences, is a constant.
Fig. 1: Heat flow between two solids in contact and the temperature distribution. When two solid bodies come in contact, such as A and B in Figure 1, heat flows from the hotter body to the colder body. From experience, the temperature profile along the two bodies varies, approximately, as shown in the figure. A temperature drop is observed at ...